thermo90st-repair.pdf

Webasto Thermo 90 ST - - dziwny objaw z pompą impulsową

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Water heaters

Workshop manual

Thermo 90 S
Thermo 90 S-ADR
(Transport of hazardous goods)

Thermo 90 ST
Thermo 90 ST-ADR
(Transport of hazardous goods)

08/2004

Thermo 90 S / Thermo 90 ST

Table of contents
Table of contents

1

Introduction
1.1
1.2
1.3
1.4

Contents and purpose ........................................................................................................................... 101
Meaning of signal words ........................................................................................................................ 101
Additional documentation to be used..................................................................................................... 101
Safety instructions and regulations........................................................................................................ 101
1.4.1 General safety regulations........................................................................................................... 101

1.5
1.6
2

General description
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
2.10
2.11

3

Statutory regulations governing installation ............................................................................................102
Suggestions for improvements and modifications ................................................................................. 102

Combustion air fan................................................................................................................................. 202
Heat exchanger ..................................................................................................................................... 202
Temperature sensor .............................................................................................................................. 203
Temperature limiter................................................................................................................................ 203
Burner insert .......................................................................................................................................... 203
Glow plug............................................................................................................................................... 203
Flame monitor........................................................................................................................................ 203
Combustion pipe.................................................................................................................................... 203
Circulating pump.................................................................................................................................... 203
Control unit ............................................................................................................................................ 203
Metering pump....................................................................................................................................... 203

Function description
3.1
3.2
3.3
3.4
3.5
3.6

Switching on .......................................................................................................................................... 301
Heating mode ........................................................................................................................................ 301
Control mode ......................................................................................................................................... 301
Switching off .......................................................................................................................................... 302
Heater functions when installed in ADR vehicles .................................................................................. 302
Malfunctions........................................................................................................................................... 303
3.6.1 Fault lock-out ............................................................................................................................... 303
3.6.2 Diagnosis after fault lock-out, Thermo 90 S and Thermo 90 ST ................................................. 304

4

Technical data ................................................................................................................................................ 401

5

Troubleshooting
5.1
5.2
5.3
5.4

General .................................................................................................................................................. 501
General fault indications ........................................................................................................................ 501
Fault indications on fault lock-out .......................................................................................................... 502
Visual check for assessing the burner ................................................................................................... 503
5.4.1
5.4.2
5.4.3
5.4.4

Burner housing .............................................................................................................................503
Back wall with metal evaporator .................................................................................................. 504
Combustion chamber .................................................................................................................. 504
Complete burner.......................................................................................................................... 504

I

Table of contents
6

Thermo 90 S / Thermo 90 ST

Function tests
6.1
6.2

General ................................................................................................................................................. 601
Settings ................................................................................................................................................. 601
6.2.1 Setting the CO2 content.............................................................................................................. 601

6.3

Testing individual components.............................................................................................................. 601
6.3.1
6.3.2
6.3.3
6.3.4

7

601
601
601
601

Circuit diagrams
7.1

8

Resistance test of the temperature sensor .................................................................................
Resistance test of the glow plug .................................................................................................
Resistance test of the flame monitor ..........................................................................................
Testing the combustion air fan....................................................................................................

General ................................................................................................................................................. 701

Service work
8.1
8.2
8.3
8.4
8.5
8.6

801
801
801
802
802
804

8.6.1
8.6.2
8.6.3
8.6.4
8.6.5
8.6.6
8.7

General .................................................................................................................................................
Work on the heater ...............................................................................................................................
Work on the vehicle ..............................................................................................................................
Heater trial run ......................................................................................................................................
Service work .........................................................................................................................................
Visual inspections and installation instructions .....................................................................................

804
804
807
807
807
808

Removal and installation....................................................................................................................... 808
8.7.1
8.7.2
8.7.3
8.7.4
8.7.5

8.8

II

Connection to the vehicle cooling system...................................................................................
Connection to the vehicle fuel system ........................................................................................
Metering pump with damper .......................................................................................................
Fuel filter .....................................................................................................................................
Combustion air supply ................................................................................................................
Exhaust line ................................................................................................................................

Heater, removal and installation .................................................................................................
Changing the circulating pump ...................................................................................................
Changing the temperature limiter ...............................................................................................
Changing the temperature sensor ..............................................................................................
Changing the combustion air fan ................................................................................................

808
809
809
809
809

Start-up ................................................................................................................................................. 809

Thermo 90 S / Thermo 90 ST
9

Table of contents

Repair
9.1

General .................................................................................................................................................. 901
9.1.1 Work on stripped-down components ........................................................................................... 901

9.2

Dismantling and assembling.................................................................................................................. 902
9.2.1
9.2.2
9.2.3
9.2.4
9.2.5
9.2.6
9.2.7
9.2.8

10

Electrical connections (Thermo 90 S).......................................................................................... 902
Changing the circulating pump .................................................................................................... 903
Changing the temperature limiter ................................................................................................ 904
Changing the temperature sensor ............................................................................................... 904
Changing the combustion air fan................................................................................................. 906
Changing the burner, flame monitor and glow plug..................................................................... 907
Changing the burner head........................................................................................................... 909
Changing the heat exchanger ..................................................................................................... 910

Packing, storage and shipment
10.1 General ................................................................................................................................................ 1001

III

List of illustrations

Thermo 90 S / Thermo 90 ST
List of illustrations

301

Sequence of functions ............................................................................................................................... 302

501
502
503
504
505

General fault indications ............................................................................................................................
Fault indications on fault lock-out ..............................................................................................................
Visual check, burner back wall...................................................................................................................
Visual check, pilot flame outlet opening.....................................................................................................
Visual check, complete burner...................................................................................................................

501
502
503
504
504

701
702

702

707
708

System circuit for Thermo 90 S, 12 and 24 V, with standard clock............................................................
System circuit for Thermo 90 S, 12 and 24 V, with standard clock and separate
circulating pump control .............................................................................................................................
System circuit for Thermo 90 S-ADR, 24 V, with switch ............................................................................
System circuit for Thermo 90 S-ADR, 24 V, with switch without power take-off ........................................
System circuit for Thermo 90 ST, 12 and 24 V, with standard digital timer ...............................................
System circuit for Thermo 90 ST, 12 and 24 V, with standard digital timer and separate
circulating pump control .............................................................................................................................
System circuit for Thermo 90 ST-ADR, 24 V, with switch..........................................................................
System circuit for Thermo 90 ST-ADR, 24 V, with switch without power take-off......................................

801
802
803
804
805
806
807
808
809

Specimen installations for heater in a truck ...............................................................................................
Fuel supply.................................................................................................................................................
Webasto fuel extractor ...............................................................................................................................
Fuel extraction from the plastic tank (extraction through tank drain screw) ...............................................
Fuel extraction from the plastic tank (extraction through tank fitting).........................................................
Webasto fuel extractor ...............................................................................................................................
Pipe/hose connection.................................................................................................................................
Metering pump, installation position and attachment ................................................................................
Exhaust pipe opening, installation position ................................................................................................

803
804
805
805
805
806
806
807
808

901
902
903
904
905
906

Electrical connections (Thermo 90 S) ........................................................................................................
Changing the circulating pump ..................................................................................................................
Changing the temperature limiter and temperature sensor .......................................................................
Changing the combustion air fan ...............................................................................................................
Changing the burner, flame monitor and glow plug ...................................................................................
Changing the burner head .........................................................................................................................

902
903
905
906
908
909

703
704
705
706

IV

703
704
705
706
707
708
709

Thermo 90 S / Thermo 90 ST

1 Introduction

1

Introduction

1.4.1 General safety regulations

1.1

Contents and purpose

The year of first start-up must be indelibly identified
on the rating plate by removing the corresponding
year number.

This workshop manual is designed to assist trained
personnel with repairing both the petrol and the diesel
versions of the Thermo 90 S und Thermo 90 ST water
heaters.

The heaters are only licensed for heating the motor
vehicle engine and vehicle cabin, not however for heating
the hazardous material transport space.

The heater is only allowed to be operated with the
intended fuel (diesel or also with heating oil EL) and only
in the particular prescribed electrical connection type.

The heater is only allowed to be installed in motor vehicles
or in independent heating systems with a minimum
coolant volume of 6 litres.

1.2

Meaning of signal words

Throughout this manual, the signal words WARNING,
CAUTION and NOTE have the following meanings:
WARNING
This heading is used to highlight operating instructions or
procedures which, if not or not correctly followed, may
result in personal injury or fatal accidents.
CAUTION
This heading is used to highlight operating instructions or
procedures which, if not or not correctly followed, may
result in damage to the equipment or its components.
NOTE
This heading is used to direct your attention to a special
feature deemed essential to highlight.

1.3

Additional documentation to be used

This workshop manual contains all necessary information
and instructions for repairing Thermo 90 S and Thermo 90 ST
water heaters.
Normally, there is no need to use additional
documentation.
If required, the installation instructions, the vehiclespecific installation instructions and the operating
instructions can be used as well.

1.4

Safety instructions and regulations

In principle, the general accident prevention regulations
and current works safety instructions are applicable.
The "General safety regulations" that go beyond the
scope of the above regulations are stated below.
Any special safety regulations relevant to this instruction
manual will be highlighted in the relevant sections or text
passages of the procedures.

The heater is not allowed to be installed in the driver's cab
or passenger compartment of vehicles. If the heater is
nevertheless installed in such a place, the installation box
must be tightly sealed against the vehicle interior. The
installation box must have sufficient external ventilation to
ensure that a maximum temperature of 40 °C is not
exceeded in the box. Malfunctions may occur if the
temperature exceeds this level.
WARNING
The heater must not be operated in enclosed areas,
such as garages or workshops without an exhaust
emissions extraction system, not even using the
timer or Telestart, because of the risk of asphyxiation
and poisoning.
The heater must be switched off at filling stations and
fuel tank farms because of the risk of explosion.
CAUTION
Wherever inflammable vapours or dust may form (for
example near fuel, coal, wood dust or cereal stores or
the like), the heater must be switched off because of
the risk of explosion.
A temperature of 85 °C (storage temperature) must not be
exceeded in the vicinity of the control unit (for example
when completing painting work on the vehicle).
If this temperature is exceeded, the electronic systems
may suffer permanent damage.
Follow the instructions supplied by the vehicle
manufacturer to check the cooling water level. The water
in the heating circuit of the heater must contain at least
10% branded anti-freeze.
Non-compliance with the installation instructions and the
warnings contained therein will lead to the exclusion of all
liability by Webasto. The same applies if repairs are
carried out incorrectly or with the use of parts other than
genuine spare parts. This will result in the revocation of
the type licence for the heater and therefore the general
operating licence for the vehicle.

101

1 Introduction
1.5

Statutory regulations governing
installation

Refer to the installation instructions for the statutory
regulations if necessary.

Thermo 90 S / Thermo 90 ST
1.6

Suggestions for improvements and
modifications

Complaints, improvement suggestions or corrections
relating to this technical manual should be addressed to:
Webasto Thermosysteme International GmbH
Technical Documentation Dept.
D-82131 Stockdorf
Tel.: +49 (89) 8579 4542
Fax: +49 (89) 8579 4757

102

Thermo 90 S / Thermo 90 ST
2

2 General description

General description

2 hours after the heater is switched on.
The Thermo 90 S and Thermo 90 ST heater is principally
composed of

Thermo 90 S and Thermo 90 ST water heaters operate in
conjunction with the vehicle's own heating system and
serve
-
-
-

-
-
-
-

to heat the cab,
to defrost the vehicle windows and
to preheat water-cooled engines.

the combustion air fan
the heat exchanger
the burner insert with combustion pipe
the circulating pump

To control and monitor it, the heater has

The water heater operates independently of the engine
and is connected to the cooling system, the fuel system
and the electrical system of the vehicle.

-
-
-
-
-

The concept of the heater is based on the evaporator
principle. It is controlled by the temperature sensor and
operates intermittently.

a control unit (external)
a flame monitor
a glow plug
a temperature sensor
a temperature limiter

inside it.

Depending on the deviation between the current coolant
temperature and the nominal value measured at the
temperature sensor, the burner power is regulated
between the limits of 1.8 to 7.6 kW in diesel heaters and
1.8 to 7.6 kW in petrol heaters. When the heating
requirement is particularly high (preheating), diesel
heaters provide a maximum power of 9.1 kW for up to

In the case of the Thermo 90 S heater, the control unit can
also be flange-mounted on the combustion air fan.
The Thermo 90 ST heater is delivered with the control unit
already flange-mounted on the combustion air fan.

4

0S

3

9
mo

er

Th

2

5

1
6

7
9
11

8

10

1
2
3
4
5
6
7
8
9
10
11

Combustion air fan
Fuel connection
Temperature sensor
Temperature limiter
Heat exchanger
Inlet, coolant
Circulating pump
Outlet, coolant
Outlet, exhaust gas
Inlet, combustion air
Control unit (can also be
arranged externally in the
vehicle)

Thermo 90 S heater

201

2 General description

Thermo 90 S / Thermo 90 ST
4
3

2
1

5

6

11

8

9

1
2
3
4
5
6
7
8
9
10
11

7

10

Combustion air fan
Fuel connection
Temperature sensor
Temperature limiter
Heat exchanger
Inlet, coolant
Circulating pump
Outlet, coolant
Outlet, exhaust gas
Inlet, combustion air
Control unit

Thermo 90 ST heater

2.1

Combustion air fan

The combustion air fan supplies the air required for the
combustion process from the combustion air inlet to the
burner insert.

2.2

Heat exchanger

In the heat exchanger, the heat generated by combustion
is transferred to the coolant circuit.
Temperature limiter
Temperature sensor

Combustion air fan
202

Heat exchanger

Thermo 90 S / Thermo 90 ST
2.3

Temperature sensor

2.8

The temperature sensor records the coolant temperature
at the coolant outlet of the heater as an electrical
resistance. This signal is fed to the control unit where it is
processed.

2.4

2 General description
Combustion pipe

The mixture of fuel and air burns in the combustion pipe,
thus causing the heat exchanger to become hot.

Temperature limiter

The overheating guard circuit (bimetallic) protects the
heater against impermissibly high operating
temperatures. The overheating guard circuit trips if the
heat exchanger temperature exceeds 127 ?7 °C and
switches off the heater.

2.5

Burner insert

The fuel is distributed over the burner cross-section in the
combustion pipe in the burner insert.

2.6

Glow plug

The mixture of fuel and air is ignited by the glow plug when
the heater is started. The glow plug takes the form of an
electrical resistor and is positioned in the burner insert on
the side away from the flame.

Combustion pipe

2.9

Circulating pump

The circulating pump ensures that coolant is pumped
through the vehicle and heater circuits. The pump is
switched on by the control unit and it runs throughout
operation of the heater (including in the control pause).

Burner insert

Glow plug

Circulating pump

2.10 Control unit

Flame monitor

2.7

Flame monitor

The flame monitor is a low-ohm PTC resistor, which
changes its resistance depending on the heat emitted by
the flame. The signals are fed to the control unit where
they are processed. The flame status is monitored by the
flame monitor whenever the heater is operating.

The control unit is the central component. It guarantees
the sequence of functions and monitoring of combustion
mode. It is flange-mounted on the combustion air fan,
although in the case of the Thermo 90 S it may be
installed externally in the vehicle.

2.11 Metering pump
The fuel supply and metering for the heater is assured by
an external metering pump. It addition, it serves as a shutoff element when the heater is switched off.
The solenoid coil of the metering pump receives its pulses
from the microprocessor in the control unit.

203

2 General description

Page for notes
204

Thermo 90 S / Thermo 90 ST

Thermo 90 S / Thermo 90 ST
3

Function description
(Fig. 301)

3.1

3 Function description

Switching on

The "operating indicator" on the digital timer lights up
when the "immediate heating" button is pressed.
or
When switching on with the switch, the operating indicator
in the switch lights up.
The circulating pump, glow plug and combustion air fan
start operating.

3.2

Heating mode

Combustion starts after approx. 60 to 140 seconds.
Automatically controlled heating operation runs at full load
for a maximum of 2 hours.
The vehicle's own heater fan does not switch on until the
heat carrier (coolant) has heated up sufficiently. Once the
preset nominal temperature has been reached (see table
of regulating temperatures) the heating power is reduced
to the lowest part load in small individual steps.

3.3

Control mode

The heater switches to the control pause if the
temperature of the coolant continues to rise to the
threshold of the control pause. The circulating pump, the
vehicle's own heater fan and the operating indicator
continue to operate during the control pause.
The heater restarts when the coolant cools to the preset
temperature for switching back on.
Diesel heaters
If the water temperature in the heater is higher than the
nominal temperature but has not yet reached the
threshold for the control pause and if the temperature then
falls back to the nominal temperature within 10 minutes
(after reaching this temperature for the first time), the
heater switches back to the 9.0 kW heating stage.
When the nominal temperature is reached, the heater is
only switched back on again up to the 7.6 kW heating
stage.
Petrol heaters
The maximum heating power in petrol heaters is
always 7.6 kW.

301

3 Function description
2
1 3

A

5
4

Thermo 90 S / Thermo 90 ST

7
6

12
8

9

10

11

15
13

14

18
16

17

22
19

20

21

23

* If no flame is formed, the
start is automatically
repeated (20 s pulse preglow, 90 s safety time).

1
0
1
/4
0

B

1

C

1

D

1
0

E

1
0

F

1
0

G

1

1
/2
1/4
0

*

0
30

80

90

75

70

°C ?

o Possible regulating
temperatures that can be
set, see table below

Safety time

Fig. 301 Sequence of functions

3.4

Switching off

The operating indicator on the digital timer/switch goes
out when the heater is switched off. The combustion
process will be ended and the run-on phase will start.
The circulating pump and the combustion air fan continue
to run, however, in order to cool down the heater (run-on)
and are switched off automatically after approx.
105 seconds. The heater may be switched on again
during the run-on time.
The temperature in the cabin can also be controlled using
the vehicle's own heater fan with a cabin thermostat.

3.5

Heater functions
when installed in ADR vehicles

The heater is started using the switch. An ADR case
(constrained shut-off) is triggered when
-
-

the vehicle's engine is switched off,
a pumping device is started,

in which case the short run-on is terminated after
20 seconds (Thermo 90 S) and after 40 seconds
(Thermo 90 ST).
Following this, the control unit is left in the "fault lock-out"
status. The on/off switch must be moved to "Off" before it
can be restarted.
The disconnecting switch (emergency off switch) is only
allowed to be used in case of danger, because the heater
is switched off without any run-on (overheating possible).

Sequence of functions for Thermo 90 S and ST
1
2
3
4
5
6
7
8
9
10
11
12

302

Switch on
Component interrogation
Pre-glow 40 s (pulsed)
Metering pump supply 5 - 7 s (1)
Metering pump / part load (1/4)
Flame monitor take-over
Stabilisation time
Full load
Vehicle fan "On"
Control range
Control pause
Flame monitor "Cold" (0)

13
14
15
16
17
18
19
20
21
22
23

Run-on ended
Pre-glow 15 - 20 s (pulsed)
Metering pump supply 5 - 7 s (1)
Metering pump / part load (1/4)
Flame monitor take-over
Stabilisation time
Coolant temperature reduced
Full load
Switch off (run-on)
Flame monitor "Cold" (0)
Run-on ended

Thermo 90 S / Thermo 90 ST
A
B
C
D
E
F
G

3.6

3 Function description

Glow plug
Metering pump
Combustion air fan
Flame monitor
Operation indicator light
Circulating pump
Vehicle fan

Malfunctions

3.6.1 Fault lock-out
Fuel is supplied for max. 240 seconds if the flame does
not start to burn.
Fuel is supplied for max. 240 seconds if the flame goes
out during operation.
The fuel supply is shut off if the system overheats
(temperature limiter is tripped). If the system overheats,
the button on the temperature limiter must be reset.
Once the cause of the fault has been eliminated, the fault
lock-out is cancelled by switching the heater off and on
again.
If the undervoltage guard switches off the system
Thermo 90 S and Thermo 90 ST
12 volts

10.5 V - 0.5 V

24 volts

21 V -1 V

for longer than 20 seconds, the fuel supply is interrupted.
CAUTION
A forced reset of the return spring when hot can result in
damage to the component.

303

3 Function description
3.6.2 Diagnosis after fault lock-out
Thermo 90 S and Thermo 90 ST
Check the fuses and plug connectors.
3.6.2.1 Version with digital timer
If the system is equipped with a standard clock, a fault
message appears on the display of the digital timer after
a fault occurs:
F
F
F
F
F

01
02
03
04
05

F 06
F 07
F 08
F 09
F 10
F 11

304

No start (after 2 attempts to start)
Flame failure
Undervoltage or overvoltage
Premature flame recognition
Flame monitor interrupt or flame monitor short
circuit
Temperature sensor interrupt or temperature
sensor short circuit
Metering pump interrupt or metering pump short
circuit
Fan motor interrupt or fan motor short circuit or
fan motor incorrect speed
Glow plug interrupt or glow plug short circuit
Overheating
Circulating pump interrupt or circulating pump
short circuit

Thermo 90 S / Thermo 90 ST
3.6.2.2 Version with switch
If the system is operated with a switch, the nature of the
fault is indicated by a flashing code on an operating
indicator light during the run-on time of the heater.
After five short signals, count the long flashes:
1x
2x
3x
4x
5x
6x
7x
8x
9x
10x
11x

No start (after 2 attempts to start)
Flame failure
Undervoltage or overvoltage
Premature flame recognition
Flame monitor interrupt or flame monitor short
circuit
Temperature sensor interrupt or temperature
sensor short circuit
Metering pump interrupt or metering pump short
circuit
Fan motor interrupt or fan motor short circuit or fan
motor incorrect speed
Glow plug interrupt or glow plug short circuit
Overheating
Circulating pump interrupt or circulating pump short
circuit

Thermo 90 S / Thermo 90 ST

3 Function description

Page for notes
305

Thermo 90 S / Thermo 90 ST
4

4 Technical data

Technical data
Fuel for Thermo 90 S / Thermo 90 ST and Thermo 90
S-ADR / Thermo 90 ST-ADR (diesel):
The diesel fuel specified by the manufacturer must be
used.
We know of no negative influences due to additives. If fuel
is extracted from the vehicle's tank, follow the additive
instructions issued by the vehicle manufacturer.
If you change to low-temperature fuel, the heater must be
operated for approx. 15 minutes so that the fuel line and
fuel pump are filled with the new fuel.

Except where limit values are specified, the technical data
below refer to the usual heater tolerances of ?10% at an
ambient temperature of +20 °C and at the rated voltage.
Electrical components
The control unit, motors for combustion air fan and
circulating pump, glow plug, switch and digital timer (no
timer for ADR mode) are designed for either 12 volts or
24 volts.
The temperature limiter, temperature sensor and flame
monitor are identical on 12 V and 24 V heaters.
Fuel for Thermo 90 S / Thermo 90 ST petrol:
The fuel specified by the manufacturer must be used.
Both leaded and unleaded fuel may be used.

Heater

Operation

EC licensing symbol

Thermo 90 S
Petrol

Thermo 90 ST
Petrol

Thermo 90 S diesel Thermo 90 ST diesel
Thermo 90 S-ADR Thermo 90 ST-ADR

~S299

~S298

Model

Water heater with Ferro-Tec technology

Heat output

Max.
regulating
range

2.0 kW - 7.6 kW

9.1 kW
1.8 kW - 7.6 kW

Petrol

Diesel

0.25 l/h - 1.0 l/h

1.1 l/h
0.19 l/h - 0.9 l/h

Fuel
Fuel consumption

Max.
regulating
range

Rated voltage

12 volts

12 or 24 volts

Operating voltage range

10 ... 15 volts

10 ... 15 or 20 ... 30 volts

Nominal power consumption with circulating Max.
regulating
pump
range
(without vehicle fan)

37 W - 83 W

90 W
37 W - 83 W

Max. ambient temperature:
Heater:
- Operation

-40 ... +110 °C (90 °C with control unit installed on heater)

- Storage
Control unit:

-40 ... +110 °C (90 °C with control unit installed on heater)

- Operation

-40 ... +75 °C

-40 ... +85 °C

- Storage
Metering pump: - Operation

-40 ... +20 °C

- Storage
Permitted operating pressure (heat carrier)

-40 ... +75 °C

-40 ... +85 °C

-40 ... +85 °C
-40 ... +40 °C
-40 ... +85 °C
Max.

2.0 bar

Capacity of the heat exchanger

0.15 l

Max. combustion air intake temperature

+40 °C

Minimum capacity of the circuit

6.00 l

Delivery rate of the circulating pump
against 0.15 bar

1650 l/h

CO2 in exhaust fumes (permitted function
range)

Max.

10 ... 12.0% by volume

CO2 adjustment values at approx. +20 °C
and geographic altitude above sea level

Max.

0 m 500 m 1000 m
10% 10.6% 11.3%

Heater dimensions (tolerance ? 3 mm)
* Control unit installed on the heater
Weight

L 310 (355*) mm
W 131 mm
H 232 mm

L 307 (352*) mm
W 131 mm
H 232 mm

L 310 (355*) mm
W 131 mm
H 232 mm

L 307 (352*) mm
W 131 mm
H 232 mm

4.8 kg

401

4 Technical data

Page for notes
402

Thermo 90 S / Thermo 90 ST

Thermo 90 S / Thermo 90 ST
5

Troubleshooting

5.1

General

This section describes how to identify and remedy faults
on the Thermo 90 S und Thermo 90 ST heater.
CAUTION
Troubleshooting work demands precise knowledge of the
structure and theory of operation of the various
components and must be carried out by trained personnel
only.
If in doubt, refer to sections 2 and 3 for a description of
how the functions interact.

5 Troubleshooting
CAUTION
As a rule, fault detection is restricted to the localisation of
defective components.
The following potential sources of malfunctions are not
taken into account and should always be checked so that
they can then be excluded as the cause of the particular
fault:
o
o
o
o
o
o

Corroded plugs
Loose plug contacts
Poor crimp contacts on plugs
Corroded cables and fuses
Corroded battery terminals
Impermissibly high ambient temperature

Conduct a function test in the vehicle after rectifying each
fault; switch the heater off and back on again first.

5.2

General fault indications

The following table (Fig. 501) lists the possible general
fault indications.

Fault indication

Possible cause

Remedy

Heater switches off
automatically

No combustion after start and
restart

Control unit enters fault lock-out status.
Switch the heater off and back on again.

Flame extinguishes during
operation

Contact a Webasto service centre if heater
operation does not start again

Heater overheats due to lack/
loss of coolant

Top up coolant.
After the unit has cooled down, press the
button of the temperature limiter before
switching on or fit a new temperature limiter

Voltage failure
longer than 20 seconds

Check fuses, plug connectors and charge
condition of the battery

Switch off by temperature limiter

After the unit has cooled down,
press the button of the temperature limiter
before switching on or fit a new temperature
limiter

No flame recognition on start

Check flame monitor and connections

Fig. 501 General fault indications

NOTE
In many cases, the burner may be one possible cause.
Perform a visual check in accordance with 5.4.

501

5 Troubleshooting
5.3

Thermo 90 S / Thermo 90 ST

Fault indications on fault lock-out

NOTE
If the system is operated with a switch, the nature of the
fault is indicated by a flashing code on an indicator light
during the run-on time of the heater.

After five short signals, count the long flashes.
In the Thermo 90 S heater with a standard clock, the fault
is output on the clock display (see 3.6.3). The following
table can be used accordingly.

Fault indication

Possible cause

Remedy

No function

Electrical cabling,
fuses

Check fuses
Check battery connections:
+ on 12 / - on 9 / + on 3, plug X12
(Thermo 90 S)
+ on 12 / - on 9 / + on 3, plug X8
(Thermo 90 ST)

Control unit defective

Replace control unit

Fuel system

Check fuel level
Check fuel filter
Bleed fuel system

Combustion air/exhaust line

Check combustion air/exhaust line for
foreign bodies and clean if necessary

Burner

Clean burner and change if necessary

Fuel supply

Check fuel level
Check fuel filter
Bleed fuel system

Burner

Clean burner and change if necessary

3 Flashing pulses
(undervoltage)

Electrical power supply

Check battery
Check electrical connections

4 Flashing pulses
(flame monitor continuously
hot)

Flame monitor defective

Replace flame monitor

5 Flashing pulses
(flame monitor defective)

Cabling

Check cabling for damage, discontinuity and
short-circuit

Flame monitor defective

Replace flame monitor

Cabling

Check cabling for damage, discontinuity and
short-circuit

Temperature sensor defective

Replace temperature sensor

Coolant circuit

Check coolant level
Bleed coolant circuit
Reset temperature limiter

Cabling

Check cabling for damage, discontinuity and
short-circuit

Metering pump defective

Replace metering pump

Cabling

Check cabling for damage, discontinuity and
short-circuit

Combustion air fan defective

Replace combustion air fan

1 Flashing pulse
(start did not occur)

2 Flashing pulses
(flame failure during burner
operation)

6 Flashing pulses
(temperature sensor
defective)

7 Flashing pulses
(metering pump defective/
(overheating guard circuit
defective)

8

Flashing pulses
(combustion air fan
defective)

Fig. 502 Fault indications on fault lock-out (page 1 of 2)
502

Thermo 90 S / Thermo 90 ST

5 Troubleshooting

Fault indication

Possible cause

Remedy

9 Flashing pulses
(glow plug defective)

Cabling

Check cabling for damage, discontinuity and
short-circuit

Flow plug defective

Replace glow plug

10 Flashing pulses
(overheating)

Heater overheats

Check coolant and top up if necessary.
After the unit has cooled down, press the
button of the temperature limiter before
switching on or fit a new temperature limiter

11 Flashing pulses
(circulating pump defective)

Cabling

Check cabling for damage, discontinuity and
short-circuit

Circulating pump defective

Replace circulating pump

Fig. 502 Fault indications on fault lock-out (page 2 of 2)

5.4

Visual check for assessing
the burner

5.4.1 Burner housing
o

The burner and the evaporator in the heater display
specific characteristics when they must be replaced or do
not have any fault source.
The criteria of a correct check are listed below.

The start air hole (Fig. 503) must be clear otherwise
no start will occur.
Remedy
Carefully remove impurities from the start air hole
(e.g. using a 1.5 mm diameter wire). Remove the glow
plug first.

1

9

2

8

3

1
2
3
4
5
6
7
8
9

Fuel pipe
Round seal
Flame monitor
Insulation
Glow plug
Housing
Screw
Bar
Start air hole

4
7
6

5
Fig. 503 Visual check, burner back wall

503

5 Troubleshooting

Thermo 90 S / Thermo 90 ST

5.4.2 Back wall with metal evaporator

5.4.3 Combustion chamber

o

o

The pilot flame outlet opening (Fig. 504) must be clear
otherwise no start will occur.
Remedy
Replace burner

o

o

Cracks, flaking as well as black or other discoloration
of the evaporator do not lead to burner failure and are
not significant.

The combustion chamber (Fig. 505) should not be
damaged (e.g. dented). A dented combustion
chamber can lead to poor combustion or carbon buildup in the heater.
Remedy
Replace burner

o

Coke deposits on the evaporator surface (except for
the pilot flame outlet opening) are normal; as a rule,
the burner cleans itself due to the load changes from
full load to part load and part load to full load.

The air holes (Fig. 505) in the combustion chamber
must not be blocked up by carbon deposits. If the air
holes are blocked up by carbon deposits, this may
result in failure of combustion to start or to run
effectively.
Remedy
Carefully scratch clear the air holes

Pilot flame outlet opening

5.4.4 Complete burner
o
o

The housing and the combustion chamber (Fig. 505)
must be firmly connected together and there must not
be any play (check by moving the fuel pipe slightly).

o

Pilot flame outlet opening

The screw connection of the housing and combustion
chamber (Fig. 505) must be tight.

o

Metal evaporator, petrol

The cables of the glow plug and flame monitor must
be routed as shown in Fig. 503.

The round sealing ring (Fig. 503) must evenly
surround the fuel pipe and must not leak.

o

The distance (gap) between the edge of the housing
and the top edge of the combustion chamber
(Fig. 505) does not have to be even all the way
around.

o

The insulation (Fig. 503) must not be missing.

Combustion chamber

Metal evaporator, diesel

Fig. 504 Visual check, pilot flame outlet opening

Swirl orifice

Air holes
Gap between housing
and combustion chamber
Fig. 505 Visual check, complete burner

504

Thermo 90 S / Thermo 90 ST

6 Function tests

6

Function tests

6.3.3 Resistance test on the flame monitor

6.1

General

If you conduct this electrical test with a digital multimeter,
the flame monitor should have the following values:

This section describes the tests conducted on the heater
and its settings when it is installed and not installed to
verify that it is in working order.
WARNING
The heater must not be operated in enclosed areas such
as garages and workshops without an emissions
extraction system.

Cold test:
Resistance at 25 °C:
3.0 ?0.4 Ohm
Test current:
& lt; 5 mA
Hot test:
Resistance at 800 ?20 °C:
8 ?1.0 Ohm
(ceramic rod at red heat over length of approx. 20 mm)
Test current:
& lt; 5 mA

6.3.4 Testing the combustion air fan

6.2

Settings

The motor speed test must be performed with the heater
assembled and in the operating voltage range. Listen out
for grinding noises.

6.2.1 Setting the CO2 content
It is permitted for the factory-set combustion air quantity to
be modified. This is achieved by turning the air regulating
screw.
Setting procedure
Turning clockwise: CO2 value is reduced (let the heater
run for about 5 minutes before measuring).
Rough setting: Screw the adjusting screw fully in
clockwise and then one turn back.

6.3

Testing individual components

NOTE
The cover must be removed from the fan in order to check
the motor speed. Fit a new seal before re-installing.
CAUTION
Make sure the detent lugs do not break off.
Fit a new cover and a new seal if the detent lugs have
broken off.
Speed in control range min. 1800 rpm
Speed in control range max. 5600 rpm

(?9%)
(?9%)

Fit a new combustion air fan if the speeds are outside
tolerance (see 9.2.5).

6.3.1 Resistance test of the temperature sensor
If you conduct this electrical test with a digital multimeter,
the temperature sensor should have the following values
at room temperature:
Resistance at 25 °C:
Test current:

990 ... 1010 Ohm
& lt; 1 mA

6.3.2 Resistance test of the glow plug
If you conduct this electrical test with a digital multimeter,
the glow plug should have the following values:
Glow plug:
(green)
Resistance at 25 °C:
Test current:

12 volts (red)

24 volts

0.3 ... 0.6 Ohm
& lt; 5 mA

1.3 ... 1.44 Ohm
& lt; 5 mA

601

6 Function tests

Page for notes
602

Thermo 90 S / Thermo 90 ST

Thermo 90 S / Thermo 90 ST
7

Circuit diagrams

7.1

7 Circuit diagrams

General

The circuit diagrams (Figs. 701 to 704) show the possible
circuits for the Thermo 90 S heater with
- Standard clock
- Standard clock and separate circulating pump
control
- ADR and switch
- ADR and switch, without power take-off
The circuit diagrams (Figs. 705 to 708) show the possible
circuits for the Thermo 90 ST heater with
- Standard clock
- Standard clock and separate circulating pump
control
- ADR and switch
- ADR and switch, without power take-off

701

7 Circuit diagrams

E

B3

X1

B2

Thermo 90 S / Thermo 90 ST

X1
1

2

3

X5

X3

4

5

X11 (ST 1)

X6

X12 (ST 2)

X13 (ST 3)

6
1 2

M1
M2

3
11

6

B1

12 11 10 9

8

9

7

1

12

9

2

2

11
7

5

1

3

58
15

9

2
7

5

1

3

1

1

58
15
30

30

F2

1

X6

F1

2

3

rt

rt

2

F3

11

1

X12 (ST 2)
12

P2

8

ws

5

2

A2
1 5

10

8

4

9

12

2

3

11

7

6

10

rt
86

gn

or

or

vi

bl

ge

ws/bl

X13
(ST 3)
sw

X11
(ST 1)

X3

2

1

br

9

4

bl

11
7

B4
7

4

H6
12

6

3

rt
br

H3

sw

8

gn/ws
rt/bl

2

H1

1

gr

10

vi/bl

1

87

S8

85

30

sw

br

br

87a

K5

M

4

9

1

2

0

br

gn

10

gr

3

gn

vi

11

gr

2

vi

7

br

6

bl

br

5

sw

br

ge

8

4

X5

X1
1 12

1 2

3

M

E
M2

B3

M1

B1

?

Y1

?

B2

M

A1

M3
31

31

1

Temperature coding (temperature at water outlet):
See table on page 302

2

Digital timer P2:
with positive at connection 10
heating
Connection 10 open
programmed

3

& lt; 7.5 m
0.75 mm 2

= Continuous operation with immediate

7.5 - 15 m

mm2
mm 2
mm 2
mm 2
mm 2

mm 2
mm 2
mm 2
mm 2
mm 2

0.75
1.0
1.5
2.5
4.0

= Variable heating duration can be
= (10 min to 120 min);
= Default setting 120 min

Vehicle fuse

4

Cable cross-sections
1.0
1.0
1.5
2.5
4.0
6.0

mm 2

Vehicle fan switch

Item
A1
A2
B1
B2
B3
B4
E
F1
F2
F3
H1
H3
H6

Designation
Heater
Control unit
Flame monitor
Temperature sensor
Temperature limiter/
overheating guard circuit
Cabin thermostat
Glow plug
20 A fuse
5 A fuse
20 A fuse
"Heating" symbol in the display
Symbol light
Red LED

K5
M1

Relay
Motor

Comment

Blade-type fuse SAE J 1284
Blade-type fuse SAE J 1284
Blade-type fuse SAE J 1284
Operating indicator (in item P2)
Light (in item P2)
Light in immediate heat button, ready
indicator, switch-on indicator
(in item P2)
For vehicle fan
Combustion air fan

Item
M2
M3
P2
S8

Designation
Motor
Motor
Standard clock
Momentary-contact switch

X1
X3
X5
X6
X11
X12
X13
Y1

12-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
Metering pump

Cable colours
bl
br
ge
gn
gr
or
rt
sw
vi
ws

Comment
Circulating pump
Vehicle fan
For programmed operation
Immediate heat button remote
control
To item A1
To item P2
To Y1
Diagnosis
To item A2 (ST 1)
To item A2 (ST 2)
To item A2 (ST 3)
Fuel pump for heater

Fig. 701 System circuit for Thermo 90 S, 12 and 24 V, with standard clock

702

Blue
Brown
Yellow
Green
Grey
Orange
Red
Black
Violet
White

Thermo 90 S / Thermo 90 ST

E

B3

X1

B2

X1
1

2

3

7 Circuit diagrams

X5

X3

4

5

X11 (ST 1)

X6

X12 (ST 2)

X13 (ST 3)

6
1 2

M1
M2

3
11

6

B1

12 11 10 9

8

9

7

1

12

11

9

2

2

7

1

5

3

58
15

9

2
7

5

1

3

1

1

58
15
30

30

F2
rt

X12 (ST 2)

1
12

B4
7

5

2

4

A2
X11
(ST 1)

2

3

11

7

6

10

2

1

X13
(ST 3)

rt

bl

gn

or

87a

9

12

or

87

4

gr

86

ge

br

X3

8

86

br

1 5

10

vi/bl

9

4

vi

11
7

6

K3

87

87a

K5

85

30

85

sw

30

sw

br

S8

gn/ws
rt/bl

ws

ws/bl

8

H6
12

3

3

bl

sw

8

sw

2

H1

S9

1

rt
br

P2
H3

F1

2

rt
11

10

1

X6

rt

2
1

F3

M

4

1

2

0

br

gn

9

gn

10

3

gr

vi

11

gr

2

vi

7

br

6

bl

br

5

sw

br

ge

8

4

X5

X1
1 12

1 2

3

M

E
M2

M1

B3

B1

?

Y1

?

B2

M

A1

M3
31

31

1

Temperature coding (temperature at water outlet):
See table on page 302

2

Digital timer P2:
with positive at connection 10
heating
Connection 10 open
programmed

3

& lt; 7.5 m
0.75 mm 2

= Continuous operation with immediate

0.75
1.0
1.5
2.5
4.0

= Variable heating duration can be
= (10 min to 120 min);
= Default setting 120 min

Vehicle fuse

4

Cable cross-sections

mm2
mm 2
mm 2
mm 2
mm 2

7.5 - 15 m
1.0
1.0
1.5
2.5
4.0
6.0

mm 2
mm 2
mm 2
mm 2
mm 2
mm 2

Vehicle fan switch

Item
A1
A2
B1
B2
B3
B4
E
F1
F2
F3
H1
H3
H6

Designation
Heater
Control unit
Flame monitor
Temperature sensor
Temperature limiter/
overheating guard circuit
Cabin thermostat
Glow plug
20 A fuse
5 A fuse
20 A fuse
"Heating" symbol in the display
Symbol light
Red LED

K3
K5

Relay
Relay

Comment

Designation
Motor
Motor
Motor
Standard clock
Momentary-contact switch

S9
Blade-type fuse SAE J 1284
Blade-type fuse SAE J 1284
Blade-type fuse SAE J 1284
Operating indicator (in item P2)
Light (in item P2)
Light in immediate heat button, ready
indicator, switch-on indicator (in item
P2)
For circulating pump remote control
For vehicle fan

Item
M1
M2
M3
P2
S8

Switch

X1
X3
X5
X6
X11
X12
X13
Y1

12-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
Metering pump

Cable colours
bl
br
ge
gn
gr
or
rt
sw
vi
ws

Blue
Brown
Yellow
Green
Grey
Orange
Red
Black
Violet
White

Comment
Combustion air fan
Circulating pump
Vehicle fan
For programmed operation
Immediate heat button remote
control
Heating/circulating pump remote
control
To item A1
To item P2
To Y1
Diagnosis
To item A2 (ST 1)
To item A2 (ST 2)
To item A2 (ST 3)
Fuel pump for heater

Fig. 702 System circuit for Thermo 90 S, 12 and 24 V, with standard clock and separate circulating pump control

703

7 Circuit diagrams

E

X1

B2

Thermo 90 S / Thermo 90 ST

X5

X1

B3
1

2

3

4

5

X11 (ST 1)

X6

X12 (ST 2)

X13 (ST 3)

6
1 2

M1
M2

11

B1

8

1

7

2

2

9

11
7

1

5

3

9

2
7

1

5

3

F2

F3

58
15
D+/61

1

X6

S7

2

1

X12 (ST 2)
12

F

B

H2

sw
ws

6

B4
7

5

2

3

E

8

4

A2

11

9

1 5

10

8

4

9

12

2

3

11

7

6

10

2

1

rt
86

gn

or

or

gr

vi/bl

vi

bl

rt
br

ge

ws/bl

X13
(ST 3)
sw

X11
(ST 1)

H5

Y2

87

30

sw

br

br

4

1

0

M

E
M2

M1

B3

B1

?

M

A1

M3

S5

Temperature coding (temperature at water outlet):
See table on page 302

& lt; 7.5 m
0.75 mm 2

4

Vehicle fan switch

0.75
1.0
1.5
2.5
4.0

Designation
Heater
Control unit
Flame monitor
Temperature sensor
Temperature limiter/
overheating guard circuit
Cabin thermostat
Glow plug
20 A fuse
5 A fuse
20 A fuse
Light max. 2 W
Lamp min. 1.2 W
Relay
Motor
Motor
Motor
Switch

Comment

Blade-type fuse SAE J 1284
Blade-type fuse SAE J 1284
Blade-type fuse SAE J 1284
Operating indicator (in item S4)
Switch-on indicator pumping device
For vehicle fan
Combustion air fan
Circulating pump
Vehicle fan
ON/OFF

Cable colours

Cable cross-sections

Vehicle fuse

mm2
mm 2
mm 2
mm 2
mm 2

bl
br
ge
gn
gr
or
rt
sw
vi
ws

7.5 - 15 m
1.0
1.0
1.5
2.5
4.0
6.0

mm 2
mm 2
mm 2
mm 2
mm 2
mm 2

Item
S5

Designation
1 or 2-pin disconnecting switch

S7
X1
X5
X6
X11
X12
X13
Y1
Y2

Pumping device switch
12-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
Metering pump
Solenoid valve

Blue
Brown
Yellow
Green
Grey
Orange
Red
Black
Violet
White

Comment
Emergency off switch
electrical or pneumatic
To positive
To item A1
To Y1
Diagnosis
To item A2 (ST 1)
To item A2 (ST 2)
To item A2 (ST 3)
Fuel pump for heater
For pumping device

Fig. 703 System circuit for Thermo 90 S-ADR, 24 V, with switch

704

1 2

Y1

?

B2

3

B4
E
F1
F2
F3
H2
H5
K5
M1
M2
M3
S4

2

br

9

gn

gr

10

gn

3

gr

11

2

vi

bl

M

7

vi

6

br

5

sw

br

br

ge

8

4

X5

X1
1 12

Item
A1
A2
B1
B2
B3

87a

K5
85

1

3

gn/ws
rt/bl

S4

1

br

A

F1

rt

rt

31

1

1

S5

bl

58
15
D+/61
30

12 11 10 9

3

Thermo 90 S / Thermo 90 ST

E

X1

B2

7 Circuit diagrams

X5

X1

B3
1

2

3

4

5

X11 (ST 1)

X6

X12 (ST 2)

X13 (ST 3)

6
1 2

M1
M2

11

B1

8

1

7

2

2

9

11
7

1

5

3

9

1

2
7

5

3

F2

F3

58
15
D+/61

1

X6

F1

2

1

X12 (ST 2)
12

F

B

H2

sw
ws

B4

6

7

5

2

3

E

8

4
11

gn/ws
rt/bl

S4

1

A2
9

1 5

10

8

4

9

12

2

3

11

7

6

10

2

1

rt
86

gn

or

or

gr

vi/bl

vi

bl

rt
br

ge

ws/bl

X13
(ST 3)
sw

X11
(ST 1)

br

A

87

30

br

sw

M2

Item
A1
A2
B1
B2
B3
B4
E
F1
F2
F3
H2
K5
M1
M2
M3
S4
S5

4

1

2

0

br

9

gn

gr

10

gn

3

M

E

4

11

gr

2

vi

bl

M

7

vi

6

br

5

sw

br

br

ge

8

4

X5

X1
1 12

3

87a

K5
85

br

1

3

rt

rt

31

1

1

S5

bl

58
15
D+/61
30

12 11 10 9

M1

B3

B1

?

3

Y1

?

B2

1 2

M3

M

A1

S5

Cable cross-sections

Temperature coding (temperature at water outlet):
See table on page 302

& lt; 7.5 m
0.75 mm 2

Vehicle fuse

mm2
mm 2
mm 2
mm 2
mm 2

mm 2
mm 2
mm 2
mm 2
mm 2

0.75
1.0
1.5
2.5
4.0

Vehicle fan switch

Designation
Heater
Control unit
Flame monitor
Temperature sensor
Temperature limiter/
overheating guard circuit
Cabin thermostat
Glow plug
20 A fuse
5 A fuse
20 A fuse
Light max. 2 W
Relay
Motor
Motor
Motor
Switch
1 or 2-pin disconnecting switch

7.5 - 15 m

Comment

Item
S7
X1
X5
X6
X11
X12
X13
Y1

1.0
1.0
1.5
2.5
4.0
6.0

Designation
Pumping device switch
12-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
Metering pump

mm 2

Cable colours
bl
br
ge
gn
gr
or
rt
sw
vi
ws

Blue
Brown
Yellow
Green
Grey
Orange
Red
Black
Violet
White

Comment
To positive
To item A1
To Y1
Diagnosis
To item A2 (ST 1)
To item A2 (ST 2)
To item A2 (ST 3)
Fuel pump for heater

Blade-type fuse SAE J 1284
Blade-type fuse SAE J 1284
Blade-type fuse SAE J 1284
Operating indicator (in item S4)
For vehicle fan
Combustion air fan
Circulating pump
Vehicle fan
ON/OFF
Emergency off switch
electrical or pneumatic

Fig. 704 System circuit for Thermo 90 S-ADR, 24 V, with switch without power take-off

705

7 Circuit diagrams

Thermo 90 S / Thermo 90 ST

?

1
2

Temperature coding (temperature at water outlet):
See table on page 302
Digital timer P2:
with positive at connection 10
heating
Connection 10 open
programmed

3

& lt; 7.5 m
0.75 mm 2

= Continuous operation with immediate

0.75
1.0
1.5
2.5
4.0

= Variable heating duration can be
= (10 min to 120 min);
= Default setting 120 min

mm2
mm 2
mm 2
mm 2
mm 2

7.5 - 15 m
1.0
1.0
1.5
2.5
4.0
6.0

mm 2
mm 2
mm 2
mm 2
mm 2
mm 2

Vehicle fan switch

Item
A1
A2
B1
B2
B3
B4
E
F1
F2
F3
H1
H3
H6

Designation
Heater
Control unit
Flame monitor
Temperature sensor
Temperature limiter/
overheating guard circuit
Cabin thermostat
Glow plug
20 A fuse
5 A fuse
20 A fuse
"Heating" symbol in the display
Symbol light
Red LED

K5
M1
M2
M3

Relay
Motor
Motor
Motor

Comment

Blade-type fuse SAE J 1284
Blade-type fuse SAE J 1284
Blade-type fuse SAE J 1284
Operating indicator (in item P2)
Light (in item P2)
Light in immediate heat button, ready
indicator, switch-on indicator
(in item P2)
For vehicle fan
Combustion air fan
Circulating pump
Vehicle fan

Cable colours

Cable cross-sections

Vehicle fuse

4

?

Item
P2
S8

Designation
Standard clock
Momentary-contact switch

X1
X2
X3
X4
X5
X6
X8
X9
X10
X11
Y1

4-pin plug connector
2-pin plug connector
2-pin plug connector
2-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
2-pin plug connector
12-pin plug connector
Metering pump

bl
br
ge
gn
gr
or
rt
sw
vi
ws

Comment
For programmed operation
Immediate heat button remote
control
To item A2
To item A2
To item A2
To item A2
To item A2
Diagnosis
To item A2 (ST 2)
To item P2
W-bus diagnosis
To Y1
Fuel pump for heater

Fig. 705 System circuit for Thermo 90 ST, 12 and 24 V, with standard clock
706

Blue
Brown
Yellow
Green
Grey
Orange
Red
Black
Violet
White

Thermo 90 S / Thermo 90 ST

7 Circuit diagrams

?

1

Temperature coding (temperature at water outlet):
See table on page 302

2

Digital timer P2:
with positive at connection 10
heating
Connection 10 open
programmed

3

Cable cross-sections
& lt; 7.5 m
0.75 mm 2

= Continuous operation with immediate

0.75
1.0
1.5
2.5
4.0

= Variable heating duration can be
= (10 min to 120 min);
= Default setting 120 min

Vehicle fuse

4

?

mm2
mm 2
mm 2
mm 2
mm 2

7.5 - 15 m
1.0
1.0
1.5
2.5
4.0
6.0

mm 2
mm 2
mm 2
mm 2
mm 2
mm 2

Vehicle fan switch

Item
A1
A2
B1
B2
B3
B4
E
F1
F2
F3
H1
H3
H6

Designation
Heater
Control unit
Flame monitor
Temperature sensor
Temperature limiter/
overheating guard circuit
Cabin thermostat
Glow plug
20 A fuse
5 A fuse
20 A fuse
"Heating" symbol in the display
Symbol light
Red LED

K3
K5

Relay
Relay

Comment

Designation
Motor
Motor
Motor
Standard clock
Momentary-contact switch

S9
Blade-type fuse SAE J 1284
Blade-type fuse SAE J 1284
Blade-type fuse SAE J 1284
Operating indicator (in item P2)
Light (in item P2)
Light in immediate heat button, ready
indicator, switch-on indicator
(in item P2)
For circulating pump remote control
For vehicle fan

Item
M1
M2
M3
P2
S8

Switch

X1
X2
X3
X4
X5
X6
X8
X9
X10
X11
Y1

4-pin plug connector
2-pin plug connector
2-pin plug connector
2-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
2-pin plug connector
12-pin plug connector
Metering pump

Cable colours
bl
br
ge
gn
gr
or
rt
sw
vi
ws

Blue
Brown
Yellow
Green
Grey
Orange
Red
Black
Violet
White

Comment
Combustion air fan
Circulating pump
Vehicle fan
For programmed operation
Immediate heat button remote
control
Heating/circulating pump remote
control
To item A2
To item A2
To item A2
To item A2
To item A2
Diagnosis
To item A2 (ST 2)
To item P2
W-bus diagnosis
To Y1
Fuel pump for heater

Fig. 706 System circuit for Thermo 90 ST, 12 and 24 V, with standard clock and separate circulating pump control

707

7 Circuit diagrams

Thermo 90 S / Thermo 90 ST

?

1

Temperature coding (temperature at water outlet):
See table on page 302

?

3

Vehicle fuse

& lt; 7.5 m
0.75 mm 2

4

Vehicle fan switch

0.75
1.0
1.5
2.5
4.0

Item
A1
A2
B1
B2
B3
B4
E
F1
F2
F3
H2
H5
K5
M1
M2
M3
S4

Designation
Heater
Control unit
Flame monitor
Temperature sensor
Temperature limiter/
overheating guard circuit
Cabin thermostat
Glow plug
20 A fuse
5 A fuse
20 A fuse
Light max. 2 W
Lamp min. 1.2 W
Relay
Motor
Motor
Motor
Switch

Comment

Blade-type fuse SAE J 1284
Blade-type fuse SAE J 1284
Blade-type fuse SAE J 1284
Operating indicator (in item S4)
Switch-on indicator pumping device
For vehicle fan
Combustion air fan
Circulating pump
Vehicle fan
ON/OFF

Cable colours

Cable cross-sections

mm2
mm 2
mm 2
mm 2
mm 2

bl
br
ge
gn
gr
or
rt
sw
vi
ws

7.5 - 15 m
1.0
1.0
1.5
2.5
4.0
6.0

mm 2
mm 2
mm 2
mm 2
mm 2
mm 2

Item
S5

Designation
1 or 2-pin disconnecting switch

S7
S10
X1
X2
X3
X4
X5
X6
X8
X10
X11
Y1
Y2

Pumping device switch
Switch
4-pin plug connector
2-pin plug connector
2-pin plug connector
2-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
2-pin plug connector
12-pin plug connector
Metering pump
Solenoid valve

Comment
Emergency off switch
electrical or pneumatic
To positive
Battery switch in positive
To item A2
To item A2
To item A2
To item A2
To item A2
Diagnosis
To item A2 (ST 2)
W-bus diagnosis
To Y1
Fuel pump for heater
For pumping device

Fig. 707 System circuit for Thermo 90 ST-ADR, 24 V, with switch

708

Blue
Brown
Yellow
Green
Grey
Orange
Red
Black
Violet
White

Thermo 90 S / Thermo 90 ST

7 Circuit diagrams

?

1

Temperature coding (temperature at water outlet):
See table on page 302

?

Cable cross-sections

3

Vehicle fuse

& lt; 7.5 m
0.75 mm 2

7.5 - 15 m

4

Vehicle fan switch

0.75
1.0
1.5
2.5
4.0

mm2
mm 2
mm 2
mm 2
mm 2

mm 2
mm 2
mm 2
mm 2
mm 2

Item
A1
A2
B1
B2
B3
B4
E
F1
F2
F3
H2
K5
M1
M2
M3
S4
S5

Designation
Heater
Control unit
Flame monitor
Temperature sensor
Temperature limiter/
overheating guard circuit
Cabin thermostat
Glow plug
20 A fuse
5 A fuse
20 A fuse
Light max. 2 W
Relay
Motor
Motor
Motor
Switch
1 or 2-pin disconnecting switch

Comment

Blade-type fuse SAE J 1284
Blade-type fuse SAE J 1284
Blade-type fuse SAE J 1284
Operating indicator (in item S4)
For vehicle fan
Combustion air fan
Circulating pump
Vehicle fan
ON/OFF
Emergency off switch
electrical or pneumatic

Item
S10
X1
X2
X3
X4
X5
X6
X8
X10
X11
Y1

1.0
1.0
1.5
2.5
4.0
6.0

Designation
Switch
4-pin plug connector
2-pin plug connector
2-pin plug connector
2-pin plug connector
12-pin plug connector
12-pin plug connector
12-pin plug connector
2-pin plug connector
12-pin plug connector
Metering pump

mm 2

Cable colours
bl
br
ge
gn
gr
or
rt
sw
vi
ws

Blue
Brown
Yellow
Green
Grey
Orange
Red
Black
Violet
White

Comment
Battery switch in positive
To item A2
To item A2
To item A2
To item A2
To item A2
Diagnosis
To item A2 (ST 2)
W-bus diagnosis
To Y1
Fuel pump for heater

Fig. 708 System circuit for Thermo 90 ST-ADR, 24 V, with switch without power take-off

709

7 Circuit diagrams

Page for notes
710

Thermo 90 S / Thermo 90 ST

Thermo 90 S / Thermo 90 ST
8

Service work

8.1

8 Service work

General

This section describes the service work that can be
carried out on the heater when it is installed.

8.2

Work on the heater

Disconnect the main power cable from the vehicle's
battery before carrying out any work on the heater. The
main battery power must not be disconnected whilst the
heater is operating or running on as a result of the risk of
the heater overheating and the overheating guard circuit
thus being tripped.
If you wish to carry out extensive repair work on the
heater, it may be a good idea to remove it completely.
After working on the heating circuit, top up with a coolant
mixture of water and antifreeze according to the
manufacturer's instructions and carefully bleed the
heating circuit.
Refer to the relevant installation instructions and the
installation proposal for the heater for the specific vehicle
for repairs that necessitate the installation position being
changed.

8.3

Work on the vehicle

CAUTION
A temperature of 90 °C must not be exceeded in the
vicinity of the heater in any circumstances (for example
when completing painting work on the vehicle). See
section 4.

801

8 Service work
8.4

Heater trial run

The heater must not be operated in enclosed areas such
as garages and workshops without an emissions
extraction system, even if you use the timer.

8.5

Service work

The following service work is to be carried out after or
before each heating period to maintain the functional
reliability of the heater:
o

Clean the exterior of the heater (avoid the ingress of
water).

o

Check the electrical connections for contact corrosion
and to ensure that they are secure.

o

Check the exhaust and combustion air lines for signs
of damage and to ensure that they are clear.

o

Check the fuel line and filter for leaks.

o

Check the coolant circuit and circulating pump for
leaks.

o

Inspect hoses for cracks.

o

Replace the fuel filter if there is one.

802

Thermo 90 S / Thermo 90 ST

Thermo 90 S / Thermo 90 ST

8 Service work

NOTE
The Thermo 90 S and Thermo 90 ST
heater is supplied with the control
unit mounted on the combustion air
fan.

With non-return valve and thermostat

Wiring harness
Fuel line
Exhaust line
Coolant circuit

Without non-return valve

1 Heat exchanger
vehicle heating
2 Switch for fan
of the vehicle heating
3 Relay for vehicle fan
4 Digital timer
5 Fuse strip in the car
6 Non-return valve with
leakage hole
7 T-piece
8 Vehicle engine
9 Heater
10 Circulating pump
11 Water pump
12 Radiator
13 Regulating valve
14 Exhaust muffler
15 Metering pump
16 Combustion air intake line
17 Thermostat
18 Control unit (optional on the
Thermo 90 S)
19 Control unit (installation
position of Thermo 90 ST
and optionally in
Thermo 90 S)

Fig. 801 Specimen installations for heater in a truck
803

8 Service work
8.6

Visual inspections and installation
instructions

8.6.1 Connection to the vehicle cooling system
In thermostat circuits, only use thermostats which start to
open at & lt; 65 °C.
The heater should be installed in as low a position as
possible to allow the heater and circulating pump to be
bled automatically.
This is particularly important as the circulating pump is not
self-priming.
The heater is connected to the vehicle cooling system as
shown in Fig. 801. The system must contain at least
6 litres of coolant.
The coolant hoses supplied by Webasto must always be
used. If you do not use these hoses, the hoses that you do
use must comply with DIN 73411. The hoses must be
installed without kinks and (to ensure perfect bleeding)
rising if possible.
Hose connections must be supported by hose clips to
prevent them slipping.

Thermo 90 S / Thermo 90 ST
Permissible fuel inflow
height H (m)

At max. pressure (bar) in
fuel line

0.00

0.20

1.00

0.11

2.00

0.03

Maximum fuel intake
height S (m)

At max. negative pressure
(bar) in fuel tank

0.00

-0.10

0.50

-0.06

1.00

-0.02

Only for ADR: The statutory regulation of ADR (Accord
européen relatif au transport international des
marchandises dangereuses par route) governing fuel
tanks, part 9 para. 9.2.4.7, must be adhered to.
NOTE
A sign must be affixed to the fuel filler neck warning that
the heater must be switched off before refuelling.

NOTE
The hose clips must be tightened with a torque of 4 Nm.
The cooling system must be bled carefully before using
the heater for the first time or after replacing the coolant.
The heater and lines should be installed in such a way as
to ensure static bleeding.
Perfect ventilation can be identified by the circulating
pump operating almost silently. Poor bleeding may cause
the resetting temperature limiter to trip whilst the heater is
operating.

8.6.2 Connection to the vehicle fuel system
The fuel is taken from the vehicle fuel tank or from a
separate fuel tank.
The values for the maximum pressure at the fuel
extraction point are shown in the table below.

l1 + l2 <= 10.0 m
l1
<= 1.2 m
l2
<= 8.8 m

Fig. 802 Fuel supply

804

Thermo 90 S / Thermo 90 ST

8 Service work

8.6.2.1 Fuel extraction
Vehicles with diesel engines
The fuel must be taken from the vehicle fuel tank or from
a separate tank (Figs. 803, 804 and 805).

Fuel extractor

Sealing ring

25

Hole
pattern

Tank fitting

&amp; gt; 25 mm

Only use a fuel
extractor with
metal fuel tanks

Fig. 805 Fuel extraction from the plastic tank
(extraction through tank fitting)

Fig. 803 Webasto fuel extractor
NOTE
The fitting must be made from metal!

NOTE
Deburr the cut on the fuel extractor after sawing it off and
remove any metal chips
Vehicles with petrol engines
The heater must be integrated into the return line of fuel
systems in carburettor and injection engines with a return
line.

Plastic tank

In carburettor engines without a return line the heater
must be integrated into the fuel system in the supply line
between the fuel tank and the vehicle pump.
o
o
Sealing ring

Fig. 804 Fuel extraction from the plastic tank
(extraction through tank drain screw)

NOTE
A fuel feed line can normally be identified by the fact
that a fuel filter is installed in it.
If there is an evaporation tank in the vehicle's fuel
system, the fuel must be extracted upstream of the
evaporation tank.

Fuel may only be taken from the supply or return line
using the special Webasto fuel extractor (Fig. 806). The
fuel extractor must be fitted in such a way that any air or
gas bubbles are automatically discharged towards the
tank (Fig. 806). Air or gas bubbles may be produced in the
vehicle's fuel line if there are leaks in the carburettor or
vehicle fuel pump or if the ambient temperature is higher
than the evaporation temperature of the fuel.

805

8 Service work

Thermo 90 S / Thermo 90 ST

The fuel extractor should not be located near the engine,
as gas bubbles may form in the lines on account of heat
radiated from the engine. This may cause problems
during combustion. When installing the heater in a vehicle
with fuel injection system, it is important to establish
whether the fuel pump is located inside or outside the
tank. If the fuel pump is located inside the tank, fuel can
only be extracted from the return line. In this case it must
be ensured that the return line continues almost to the
bottom of the tank and is not sealed by a non-return valve.
If this is not the case the return line may be extended. If
the fuel pump is installed outside the tank, the fuel
connection may be made between the tank and the fuel
pump.

The fuel lines must be secure at the connections using
hose clips to prevent their slipping.
Connecting two pipes with a hose
The correct procedure for connecting fuel lines with
hosing is shown in Fig. 807.
NOTE
Ensure that there are no leaks.

Correct
Clip
Wrong
Bubble

to engine
from tank

to metering pump
Fig. 806 Webasto fuel extractor
8.6.2.2 Fuel lines
Only steel, copper and plastic lines of plasticised, light and
temperature-stabilized PA 11 or PA 12 (e.g. Mecanyl
RWTL) pursuant to DIN 73378 may be used for the fuel
lines.
NOTE
Cut Mecanyl lines without burr and do not crush them. Do
not cut them with side-cutting pliers.
Since the lines normally cannot be routed with a constant
rising gradient, the internal diameter must not be allowed
to exceed a certain size. Air or gas bubbles will
accumulate in lines with an internal diameter of more than
4 mm and these will cause malfunctions if the lines sag or
are routed downwards. The diameters specified in
Figs. 802 and 806 will ensure that bubbles do not form.
The lines should not be routed downwards from the
metering pump to the heater.
Unsupported fuel lines must be secured to prevent them
sagging. They must be installed in such a way that they
cannot be damaged by flying road chippings and high
temperatures (exhaust line).

806

Bubble

Fig. 807 Pipe/hose connection

Thermo 90 S / Thermo 90 ST

8 Service work

8.6.3 Metering pump with damper

8.6.3.2 Installation and attachment

The metering pump is a combined delivery, metering and
shut-off system and is subject to certain installation
criteria (Figs. 802 and 808).

The metering pump must be secured with a vibrationdamping mounting. Its installation position is limited as
shown in Fig. 808 in order to ensure effective automatic
bleeding.

8.6.4 Fuel filter
Only a Webasto filter, order no. 487 171, is allowed to be
used if the fuel is expected to be contaminated. Install
vertically if possible, however at least horizontally.
NOTE
Note the installation position and direction of flow.

8.6.5 Combustion air supply
12 volts and 24 volts - petrol and diesel DP2

Under no circumstances may the combustion air be taken
from areas occupied by people. The combustion air intake
opening must not point in the direction of travel. It must be
located so that it cannot become clogged with dirt or snow
and cannot suck in splashing water.
The combustion air intake line (internal diameter at least
30 mm) may be 0.5 m to 5 m long with several bends
totalling 360°. Minimum bending radius is 45 mm.
The combustion air inlet must not be routed above the
exhaust outlet.

12 volts and 24 volts - diesel DP 30.2 only
Horizontal installation position
Fig. 808 Metering pump, installation position and
attachment
8.6.3.1 Installation position
Before installing the metering pump, ensure that the
maximum pressure occurring at the pickup point is less
than 0.2 bar
It is advisable to install the metering pump in a cool place.
The maximum ambient temperature must not exceed
+20 °C for petrol and +40 °C for diesel at any time during
operation.

NOTE
If the combustion air intake line cannot be installed so that
it slopes downwards, a water drain hole (with a diameter
of 4 mm) is to be made at its lowest point.
If the heater is installed in a general installation space
near the vehicle's fuel tank, the combustion air must be
taken in from the outside and the exhaust fumes
discharged into the atmosphere. The openings must be
splash-proof.
A ventilation opening measuring at least 6 cm2 is required
if the heater is installed in an enclosed box. The size of the
ventilation opening must be increased accordingly if the
temperature in the box exceeds the permitted ambient
temperature of the heater (see Technical data).

The metering pump and fuel lines must not be installed
within range of the radiated heat from hot vehicle parts.
A heat shield must be used if necessary.
The pump should ideally be installed near the tank.

807

8 Service work

Thermo 90 S / Thermo 90 ST

8.6.6 Exhaust line
The exhaust line (internal diameter 38 mm) can be
installed with a length of 0.5 m to 5 m and several bends
(360° altogether, minimum bending radius 85 mm). The
exhaust muffler is essential and must be installed near the
heater.
An attachment is required no further than 150 mm from
the end of the exhaust pipe to ensure that the angle of
90° ?10° is achieved.

-
-
-
-
-

Changing the circulating pump
Changing the temperature limiter
Changing the temperature sensor
Changing the combustion air fan
Changing the control unit (Thermo 90 S/
Thermo 90 ST)

8.7.1 Heater, removal and installation
8.7.1.1 Removal
1. Disconnect the battery.
NOTE
Only disconnect plug connectors X12 and X13 on the
control unit in the Thermo 90 S heater with the control
unit flange-mounted on the combustion air fan.

Discharge direction
almost vertical 90° ?10°

10°

10°

2. Remove the upper cover cap.
3. Disconnect the wiring harness plug from the heater.
4. Disconnect the connection for the combustion air inlet
on the heater.
5. Unfasten the hose clips and pull the coolant hoses off
the heater.
6. Disconnect the connections for the combustion air
inlet and exhaust outlet on the heater.
7. Remove three screws and washers from the heater
holder.
8. Remove the heater.
8.7.1.2 Installation

Fig. 809 Exhaust pipe opening, installation position
The opening of the exhaust pipe must not point towards
the front of the vehicle (see Figure 809).
The exhaust pipe opening must be located so that it
cannot become clogged with snow and mud.
Rigid pipes of unalloyed or alloyed steel with a minimum
wall thickness of 1.0 mm or flexible piping of alloyed steel
only must be used as the exhaust line. The exhaust pipe
is secured to the heater using a clamping collar, for
example. See the statutory regulations for other
requirements.
Only for ADR: The statutory regulation of ADR (Accord
européen relatif au transport international des
marchandises dangereuses par route) governing the
routing of the exhaust line, part 9 para. 9.2.4.7, must be
adhered to.

8.7

Removal and installation

CAUTION
When the heater is installed, only the following
dismantling or removal procedures are permitted
providing the upper cover cap is accessible and can be
removed, and there is sufficient room for removal:

808

1. Position the heater in its installation position and
screw in 3 screws with washers to attach it.
2. Connect the coolant hoses and secure with hose
clips. Tighten the hose clips to 5 Nm.
3. Secure the connection for the combustion air inlet on
the heater.
4. Secure the connections for the combustion air inlet
and exhaust outlet on the heater.
NOTE
Only reconnect plug connectors X12 and X13 on the
control unit in the Thermo 90 S heater with the control
unit flange-mounted on the combustion air fan.
5.
6.
7.
8.
9.

Connect the wiring harness plug to the heater.
Put on the top cover cap and lock it in place.
Connect the battery.
Bleed the fuel supply system.
Bleed the coolant circuit.

Thermo 90 S / Thermo 90 ST

8 Service work

8.7.2 Changing the circulating pump

8.8

NOTE
The process for changing the circulating pump is the
same irrespective of whether the heater is installed or
removed.
Change as described in 9.2.2.

After you have installed the heater, bleed the coolant
circuit and the fuel supply system carefully. Comply with
the instructions given by the vehicle manufacturer when
doing this. During the trial run, check all coolant and fuel
connections for leaks and to ensure that they are secure.
If the heater suffers a fault during operation, the fault must
be located and remedied (see section 5).

8.7.3 Changing the temperature limiter

Start-up

NOTE
The process for changing the temperature limiter is the
same irrespective of whether the heater is installed or
removed.
Change as described in 9.2.3.

8.7.4 Changing the temperature sensor
NOTE
The process for changing the temperature sensor is the
same irrespective of whether the heater is installed or
removed.
Change as described in 9.2.4.

8.7.5 Changing the combustion air fan
NOTE
The process for changing the combustion air fan is the
same irrespective of whether the heater is installed or
removed.
Change as described in 9.2.5.

809

Thermo 90 S / Thermo 90 ST
9

Repair

9.1

General

9 Repair
9.1.1.1 Cleaning
o

Clean all stripped down components.

9.1.1.2 Visual inspection
This section describes the repair work which is permitted
on the heater when it has been removed. Any further
dismantling will invalidate the warranty.
Only use the spare parts from the appropriate spare parts
kits for assembling the heater.

9.1.1 Work on stripped-down components

o
o
o

Check all components for damage (cracks,
deformation, wear, etc.) and fit new ones if necessary.
Inspect the plugs and cables for corrosion, loose
contacts, crimping faults, etc. and repair them if
necessary.
Check plug contacts for signs of corrosion and to
ensure they are secure. Repair them if necessary.

CAUTION
All seal elements between the dismantled components
must be removed and new ones fitted.

901

9 Repair
9.2

Thermo 90 S / Thermo 90 ST

Dismantling and assembling

9.2.1 Electrical connections (Thermo 90 S)
9.2.1.1 Disconnecting the electrical connections (plug
connector X1)
NOTE
All electrical connections are grouped together in the plug.
Before removing a component, first disconnect the
corresponding electrical connections.
In the Thermo 90 S heater with flange-mounted
combustion air fan, disconnect plug X1 on the heater and
plug connector X12 on the control unit. Reconnect them
after restoring the electrical connections.

1. Remove the upper cover cap from the heater.
2. Use the removing tool (hook part) to pull the locking
wedge out of the plug.
3. Use the removing tool (screwdriver part) to press the
corresponding locking lug, keep it pressed and pull
the cable out of the plug.
9.2.1.2 Making the electrical connections
1. Push the cable into the corresponding contact hole
until it locks.
2. Use the removing tool (screwdriver part) to insert the
locking wedge in the plug and press in until it locks.
3. Put on the upper cover cap.

Upper cover cap

Supplier for removing tool
(Order no. DT RT1)

Locking wedge

Compagnie Deutsch GmbH
Fraunhoferstr. 11b
D-82152 Martinsried
Tel. +49 (89) 899 1570
Fax +49 (89) 857 4684
Removing tool
Locking lug
(12 pcs.)

Fig. 901 Electrical connections (Thermo 90 S)

902

Thermo 90 S / Thermo 90 ST

9 Repair

9.2.2 Changing the circulating pump

9.2.2.2 Installation

9.2.2.1 Removal

1. Apply acid-free grease (Vaseline) to the sealing ring
(1, Fig. 902).
2. Place the circulating pump (2, Fig. 902) in the
assembly position and attach with the clip (3) and
screws (4).
3. Tighten the screws (4) to 3 Nm ?10%.
4. Connect the electrical connections (see 9.2.1.2).
5. Install the heater (see 8.7.1.2).

1.
2.
3.
4.
5.

Remove the heater (see 8.7.1.1).
Disconnect the electrical connections (see 9.2.1.1).
Remove the screws (4, Fig. 902).
Remove the clip (3) and circulating pump (2).
Complete the work on stripped-down components
(see 9.1.1).

NOTE
A Thermo 90 ST heater is shown. In the Thermo
90 S heater, the control unit can also be
arranged on the combustion air fan without
having any effect on changing the circulating
pump.

1

2

1
2
3
4

3

Sealing ring
Circulating
pump
Clip
Screw (2)

4

Fig. 902 Changing the circulating pump
903

9 Repair

Thermo 90 S / Thermo 90 ST

9.2.3 Changing the temperature limiter

9.2.4 Changing the temperature sensor

9.2.3.1 Removal

9.2.4.1 Removal

NOTE
The temperature limiter only has to be removed if it is
being replaced with a new one.
The function must be checked in the installed condition.

1. Remove the heater (see 8.7.1.1).
2. Disconnect the electrical connections (see 9.2.1.1).

1. Remove the heater (see 8.7.1.1).
2. Disconnect the electrical connections (see 9.2.1.1).
3. Remove the clip (2, Fig. 903) and pull off the
protective cap (1).
4. Use a screwdriver to lever off the retaining spring and
remove the temperature limiter (3).
5. Complete the work on stripped-down components
(see 9.1.1).
NOTE
It is essential to fit a new temperature limiter to replace a
removed one!
9.2.3.2 Installation
CAUTION
Incorrect installation will cause the heat exchanger to
melt.
1. Insert the new temperature limiter (3, Fig. 903) into the
heat exchanger (4) and press in the retaining spring.
NOTE
You must be able to hear and feel the spring clip into
the groove. Only then is the temperature limiter in the
correct installation position.
If you do not hear and feel the spring clip in:
o
o
o

Clean the contact surface of the temperature limiter
on the heat exchanger
Clean the groove in the heat exchanger
Ensure that the detent lugs are present on both sides
of the spring. Fit a new temperature limiter if
necessary.

2. Put on the protective cap (1) and secure it with the
clip (2).
3. Tighten the clip to 1 Nm ?10%.
4. Connect the electrical connections (see 9.2.1.2).
5. Install the heater (see 8.7.1.2).

904

WARNING
Leaking hot coolant can cause burns.
3. Unscrew and remove the temperature sensor
(6, Fig. 903) and remove it together with the round
sealing ring (5).
4. Complete the work on stripped-down components
(see 9.1.1).
9.2.4.2 Installation
1. Apply acid-free grease (Vaseline) to the round sealing
ring (5, Fig. 904).
2. Fit the temperature sensor (6) with the round sealing
ring (5) and screw it into the heat exchanger (4).
Tighten to 1.5 Nm ?10%.
3. Connect the electrical connections (see 9.2.1.2).
4. Install the heater (see 8.7.1.2).

Thermo 90 S / Thermo 90 ST

9 Repair

NOTE
A Thermo 90 ST heater is shown. In the
Thermo 90 S heater, the control unit can also be
arranged on the combustion air fan without
having any effect on changing the temperature
sensor.

1
1
2
3
4
5
6

Protective cap
Clip
Temperature limiter
Heat exchanger
Round sealing ring
Temperature sensor

2

3

6
4
5

Fig. 903 Changing the temperature limiter and temperature sensor
905

9 Repair

Thermo 90 S / Thermo 90 ST

9.2.5 Changing the combustion air fan

9.2.5.2 Fitting

9.2.5.1 Removal

NOTE
Insert the shaped seal (3, Fig. 904) correctly and grease it
(e.g. with Vaseline). Take care not to squash it.

1.
2.
3.
4.

Remove the heater (see 8.7.1.1).
Disconnect the electrical connections (see 9.2.1.1).
Remove the screws (2, Fig. 904).
Pull the combustion air fan (1) off the burner head (4)
and remove together with the shaped sealing ring (3).

1. Fit the new shaped sealing ring (3) onto the
combustion air fan (1). Bring the fan into the assembly
position and secure it with screws (2).
2. Tighten the screws (2) to 3 Nm ?10%.

NOTE
Remove the control unit if necessary from the
Thermo 90 S/Thermo 90 ST heater with flangemounted control unit.

NOTE
Install the control unit if necessary on the Thermo
90 S/Thermo 90 ST heater with flange-mounted
control unit.

5. Complete the work on stripped-down components
(see 9.1.1).

3. Connect the electrical connections (see 9.2.1.2).
4. Install the heater (see 8.7.1.2).

Thermo 90 S

Control unit

1
2
3
4

Combustion air
fan
Screw (2)
Shaped sealing
ring
Burner head

1

2

3

4
1
Control unit

NOTE
A Thermo 90 ST heater is shown.

Fig. 904 Changing the combustion air fan
906

Thermo 90 S / Thermo 90 ST
9.2.6 Changing the burner, flame monitor and
glow plug
9.2.6.1 Removal
1.
2.
3.
4.
5.
6.
7.
8.
9.

Remove the heater (see 8.7.1.1).
Remove the combustion air fan (see 9.2.5.1).
Remove the screw (5, Fig. 905) and washer (4).
Remove the nuts (10) and pull off the bar (8).
Pull the grommets (11 and 12) out of the slots in the
housing of the combustion pipe (3).
Pull the grommet (13) and burner (1) out of the burner
head and remove with the swirl orifice (2).
Pull the flame monitor (7) and glow plug (6) from the
burner (1) and remove.
Perform a visual check for assessing the burner
(see 5.3).
Complete the work on stripped-down components
(see 9.1.1).

9 Repair
CAUTION
During the following procedure, make sure that the
cables of the flame monitor (7) and the glow plug (6)
are routed as shown in the figure.

Glow plug

Flame monitor

9.2.6.2 Installation
1. Place the swirl orifice (2, Fig. 905) onto the burner (1).
2. Carefully insert the flame monitor (7) and glow plug (6)
into the burner up to the stop and push the grommets
(11 and 12) into the slots in the housing of the burner
pipe (3).
3. Insert the burner (1) and grommet (13) into the burner
head (3).

4. Push the insulation (9) onto the bar (8) and bring the
bar into the assembly position.
NOTE
Route the cable of the flame monitor and the glow plug
as shown in the figure!
5. Secure the bar (8) using the nuts (10). Tighten the
nuts to 3 Nm ?10%.
6. Secure the fuel line using the screw (5) and
washer (4). Tighten the screw to 3 Nm ?10%.
7. Fit the combustion air fan (see 9.2.5.2).
8. Connect the electrical connections (see 9.2.1.2).
9. Install the heater (see 8.7.1.2).

907

9 Repair

Thermo 90 S / Thermo 90 ST

NOTE
A Thermo 90 ST heater is shown.
The figure can also be used for the
Thermo 90 S heater.

1
13
12

11

6

7
8
9
10

2
4
5

3

Fig. 905 Changing the burner, flame monitor and glow plug
908

1
2
3
4
5
6
7
8
9
10
11
12
13

Burner
Swirl orifice
Burner head
Washer
Screw
Glow plug
Flame monitor
Bar
Insulation
Nut (2)
Grommet
Grommet
Grommet

Thermo 90 S / Thermo 90 ST

9 Repair

9.2.7 Changing the burner head

9.2.7.2 Installation

9.2.7.1 Removal

NOTE
The burner head and exhaust outlet port can also be
aligned during installation in the vehicle.

1. Remove the heater (see 8.7.1.1).
2. Remove the combustion air fan (see 9.2.5.1).
3. Remove the burner, flame monitor and glow plug
(see 9.2.6.1).
4. Remove the mounting screw of the V-clamping collar
(2, Fig. 906) and pull off the clamping collar.
5. Pull out and remove the burner head (1) from the heat
exchanger (3).
6. Complete the work on stripped-down components
(see 9.1.1).

1. Guide the burner head (1, Fig. 906) into the heat
exchanger (3), align it if necessary and secure with
the V-clamping collar (2).
2. If necessary, tighten the mounting screw of the
V-clamping collar to 3 Nm ?10%.
3. Install the burner, flame monitor and glow plug
(see 9.2.6.2).
4. Fit the combustion air fan (see 9.2.5.2).
5. Install the heater (see 8.7.1.2).

NOTE
A Thermo 90 ST heater is shown.
The figure can also be used for the
Thermo 90 S heater.
3
2

1
2
3

Burner head
V-clamping collar
Heat exchanger

1

Fig. 906 Changing the burner head

909

9 Repair

Thermo 90 S / Thermo 90 ST

9.2.8 Changing the heat exchanger

9.2.8.2 Installation

9.2.8.1 Removal

1. Clip the connector housing onto the heat exchanger
and insert the plug into the connector housing.
2. Install the burner head (see 9.2.7.2).
3. Install the burner, flame monitor and glow plug
(see 9.2.6.2).
4. Fit the combustion air fan (see 9.2.5.2).
5. Install the temperature sensor (see 9.2.4.2).
6. Install the temperature limiter (see 9.2.3.2).
7. Fit the circulating pump (see 9.2.2.2).
8. Install the heater (see 8.7.1.2).

1.
2.
3.
4.
5.
6.

Remove the heater (see 8.7.1.1).
Remove the circulating pump (see 9.2.2.1).
Remove the temperature limiter (see 9.2.3.1).
Remove the temperature sensor (see 9.2.4.1).
Remove the combustion air fan (see 9.2.5.1).
Remove the burner, flame monitor and glow plug
(see 9.2.6.1).
7. Remove the burner head (see 9.2.7.1).
8. Remove the plug and connector housing.
9. Complete the work on stripped-down components
(see 9.1.1).

910

Thermo 90 S / Thermo 90 ST
10

10 Packing / Storage / Shipment

Packing / Storage and Shipment

10.1 General
If the heater or its components are sent to Webasto
Thermosysteme GmbH for testing or repair, it must be
cleaned and packed in such a way that it is protected
against damage during handling, transport and storage.
CAUTION
Fully drain a complete heater before sending it back.
Make sure that no fuel or coolant can leak out during
packing and/or shipment.
Seal the coolant ports with dummy plugs.
The ambient temperatures listed in section 4 must not be
exceeded during storage.

1001

10 Packing / Storage / Shipment

Page for notes
1002

Thermo 90 S / Thermo 90 ST


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