Webasto Thermo 90 St Users Manual Thermo_90S_90ST_en

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Water heaters

08/2004

Workshop manual

Thermo 90 S

Thermo 90 S-ADR

(Transport of hazardous goods)

Thermo 90 ST

Thermo 90 ST-ADR

(Transport of hazardous goods)

Thermo 90 S / Thermo 90 ST Table of contents

I

Table of contents

1 Introduction

1.1 Contents and purpose ........................................................................................................................... 101

1.2 Meaning of signal words ........................................................................................................................ 101

1.3 Additional documentation to be used..................................................................................................... 101

1.4 Safety instructions and regulations........................................................................................................ 101

1.4.1 General safety regulations........................................................................................................... 101

1.5 Statutory regulations governing installation ............................................................................................102

1.6 Suggestions for improvements and modifications ................................................................................. 102

2 General description

2.1 Combustion air fan................................................................................................................................. 202

2.2 Heat exchanger ..................................................................................................................................... 202

2.3 Temperature sensor .............................................................................................................................. 203

2.4 Temperature limiter................................................................................................................................ 203

2.5 Burner insert .......................................................................................................................................... 203

2.6 Glow plug............................................................................................................................................... 203

2.7 Flame monitor........................................................................................................................................ 203

2.8 Combustion pipe.................................................................................................................................... 203

2.9 Circulating pump.................................................................................................................................... 203

2.10 Control unit ............................................................................................................................................ 203

2.11 Metering pump....................................................................................................................................... 203

3 Function description

3.1 Switching on .......................................................................................................................................... 301

3.2 Heating mode ........................................................................................................................................ 301

3.3 Control mode ......................................................................................................................................... 301

3.4 Switching off .......................................................................................................................................... 302

3.5 Heater functions when installed in ADR vehicles .................................................................................. 302

3.6 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 General .................................................................................................................................................. 501

5.2 General fault indications ........................................................................................................................ 501

5.3 Fault indications on fault lock-out .......................................................................................................... 502

5.4 Visual check for assessing the burner ................................................................................................... 503

5.4.1 Burner housing .............................................................................................................................503

5.4.2 Back wall with metal evaporator .................................................................................................. 504

5.4.3 Combustion chamber .................................................................................................................. 504

5.4.4 Complete burner.......................................................................................................................... 504

Table of contents Thermo 90 S / Thermo 90 ST

II

6 Function tests

6.1 General ................................................................................................................................................. 601

6.2 Settings................................................................................................................................................. 601

6.2.1 Setting the CO2 content.............................................................................................................. 601

6.3 Testing individual components.............................................................................................................. 601

6.3.1 Resistance test of the temperature sensor ................................................................................. 601

6.3.2 Resistance test of the glow plug................................................................................................. 601

6.3.3 Resistance test of the flame monitor .......................................................................................... 601

6.3.4 Testing the combustion air fan.................................................................................................... 601

7 Circuit diagrams

7.1 General ................................................................................................................................................. 701

8 Service work

8.1 General ................................................................................................................................................. 801

8.2 Work on the heater ............................................................................................................................... 801

8.3 Work on the vehicle .............................................................................................................................. 801

8.4 Heater trial run ...................................................................................................................................... 802

8.5 Service work ......................................................................................................................................... 802

8.6 Visual inspections and installation instructions ..................................................................................... 804

8.6.1 Connection to the vehicle cooling system................................................................................... 804

8.6.2 Connection to the vehicle fuel system ........................................................................................ 804

8.6.3 Metering pump with damper ....................................................................................................... 807

8.6.4 Fuel filter..................................................................................................................................... 807

8.6.5 Combustion air supply ................................................................................................................ 807

8.6.6 Exhaust line ................................................................................................................................ 808

8.7 Removal and installation....................................................................................................................... 808

8.7.1 Heater, removal and installation ................................................................................................. 808

8.7.2 Changing the circulating pump ................................................................................................... 809

8.7.3 Changing the temperature limiter ............................................................................................... 809

8.7.4 Changing the temperature sensor .............................................................................................. 809

8.7.5 Changing the combustion air fan................................................................................................ 809

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

Thermo 90 S / Thermo 90 ST Table of contents

III

9Repair

9.1 General .................................................................................................................................................. 901

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

9.2 Dismantling and assembling.................................................................................................................. 902

9.2.1 Electrical connections (Thermo 90 S).......................................................................................... 902

9.2.2 Changing the circulating pump .................................................................................................... 903

9.2.3 Changing the temperature limiter ................................................................................................ 904

9.2.4 Changing the temperature sensor ............................................................................................... 904

9.2.5 Changing the combustion air fan................................................................................................. 906

9.2.6 Changing the burner, flame monitor and glow plug..................................................................... 907

9.2.7 Changing the burner head........................................................................................................... 909

9.2.8 Changing the heat exchanger ..................................................................................................... 910

10 Packing, storage and shipment

10.1 General ................................................................................................................................................ 1001

List of illustrations Thermo 90 S / Thermo 90 ST

IV

List of illustrations

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

501 General fault indications ............................................................................................................................ 501

502 Fault indications on fault lock-out .............................................................................................................. 502

503 Visual check, burner back wall................................................................................................................... 503

504 Visual check, pilot flame outlet opening..................................................................................................... 504

505 Visual check, complete burner................................................................................................................... 504

701 System circuit for Thermo 90 S, 12 and 24 V, with standard clock............................................................ 702

702 System circuit for Thermo 90 S, 12 and 24 V, with standard clock and separate

circulating pump control ............................................................................................................................. 703

703 System circuit for Thermo 90 S-ADR, 24 V, with switch ............................................................................ 704

704 System circuit for Thermo 90 S-ADR, 24 V, with switch without power take-off ........................................ 705

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

706 System circuit for Thermo 90 ST, 12 and 24 V, with standard digital timer and separate

circulating pump control ............................................................................................................................. 707

707 System circuit for Thermo 90 ST-ADR, 24 V, with switch.......................................................................... 708

708 System circuit for Thermo 90 ST-ADR, 24 V, with switch without power take-off...................................... 709

801 Specimen installations for heater in a truck ............................................................................................... 803

802 Fuel supply................................................................................................................................................. 804

803 Webasto fuel extractor............................................................................................................................... 805

804 Fuel extraction from the plastic tank (extraction through tank drain screw)............................................... 805

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

806 Webasto fuel extractor............................................................................................................................... 806

807 Pipe/hose connection................................................................................................................................. 806

808 Metering pump, installation position and attachment ................................................................................ 807

809 Exhaust pipe opening, installation position................................................................................................ 808

901 Electrical connections (Thermo 90 S) ........................................................................................................ 902

902 Changing the circulating pump .................................................................................................................. 903

903 Changing the temperature limiter and temperature sensor ....................................................................... 905

904 Changing the combustion air fan ............................................................................................................... 906

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

906 Changing the burner head ......................................................................................................................... 909

Thermo 90 S / Thermo 90 ST 1Introduction

101

1Introduction

1.1 Contents and purpose

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 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.

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 vehicle-

specific 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.

1.4.1 General safety regulations

The year of first start-up must be indelibly identified

on the rating plate by removing the corresponding

year number.

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 installed in motor vehicles

or in independent heating systems with a minimum

coolant volume of 6 litres.

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.

1Introduction Thermo 90 S / Thermo 90 ST

102

1.5 Statutory regulations governing

installation

Refer to the installation instructions for the statutory

regulations if necessary.

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

Thermo 90 S / Thermo 90 ST 2 General description

201

2 General description

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 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.

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

2 hours after the heater is switched on.

The Thermo 90 S and Thermo 90 ST heater is principally

composed of

– the combustion air fan

– the heat exchanger

– the burner insert with combustion pipe

– the circulating pump

To control and monitor it, the heater has

– a control unit (external)

– a flame monitor

– a glow plug

– a temperature sensor

– a temperature limiter

inside it.

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.

Thermo 90 S heater

Thermo 90 S

1

2

3

4

5

6

7

8

9

10

1 Combustion air fan

2 Fuel connection

3 Temperature sensor

4 Temperature limiter

5 Heat exchanger

6 Inlet, coolant

7 Circulating pump

8 Outlet, coolant

9 Outlet, exhaust gas

10 Inlet, combustion air

11 Control unit (can also be

arranged externally in the

vehicle)

11

2 General description Thermo 90 S / Thermo 90 ST

202

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.

Combustion air fan

2.2 Heat exchanger

In the heat exchanger, the heat generated by combustion

is transferred to the coolant circuit.

Heat exchanger

1

2

3

4

5

6

7

8

9

10

11

1 Combustion air fan

2 Fuel connection

3 Temperature sensor

4 Temperature limiter

5 Heat exchanger

6 Inlet, coolant

7 Circulating pump

8 Outlet, coolant

9 Outlet, exhaust gas

10 Inlet, combustion air

11 Control unit

Temperature limiter

Temperature sensor

Thermo 90 S / Thermo 90 ST 2 General description

203

2.3 Temperature sensor

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 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.

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.

2.8 Combustion pipe

The mixture of fuel and air burns in the combustion pipe,

thus causing the heat exchanger to become hot.

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).

Circulating pump

2.10 Control unit

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 shut-

off element when the heater is switched off.

The solenoid coil of the metering pump receives its pulses

from the microprocessor in the control unit.

Burner insert

Glow plug

Flame monitor

2 General description Thermo 90 S / Thermo 90 ST

204

Page for notes

Thermo 90 S / Thermo 90 ST 3 Function description

301

3 Function description

(Fig. 301)

3.1 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.

3 Function description Thermo 90 S / Thermo 90 ST

302

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

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)

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

A

B

C

D

E

F

G

1

0

1

0

0

0

0

0

0

1

1

1

1

1

1/4

1/2

1/4

*

30 80 90 75 70 °C

23

22

212019171614131110

181512

986431

2 5 7

Safety time

❏

*If no flame is formed, the

start is automatically

repeated (20 s pulse pre-

glow, 90 s safety time).

oPossible regulating

temperatures that can be

set, see table below

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

Thermo 90 S / Thermo 90 ST 3 Function description

303

A Glow plug

B Metering pump

C Combustion air fan

D Flame monitor

E Operation indicator light

F Circulating pump

G Vehicle fan

3.6 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

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.

Thermo 90 S and Thermo 90 ST

12 volts 10.5 V - 0.5 V

24 volts 21 V -1 V

3 Function description Thermo 90 S / Thermo 90 ST

304

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 01 No start (after 2 attempts to start)

F 02 Flame failure

F 03 Undervoltage or overvoltage

F 04 Premature flame recognition

F 05 Flame monitor interrupt or flame monitor short

circuit

F 06 Temperature sensor interrupt or temperature

sensor short circuit

F 07 Metering pump interrupt or metering pump short

circuit

F 08 Fan motor interrupt or fan motor short circuit or

fan motor incorrect speed

F 09 Glow plug interrupt or glow plug short circuit

F10 Overheating

F 11 Circulating pump interrupt or circulating pump

short circuit

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 No start (after 2 attempts to start)

2x Flame failure

3x Undervoltage or overvoltage

4x Premature flame recognition

5x Flame monitor interrupt or flame monitor short

circuit

6x Temperature sensor interrupt or temperature

sensor short circuit

7x Metering pump interrupt or metering pump short

circuit

8x Fan motor interrupt or fan motor short circuit or fan

motor incorrect speed

9x Glow plug interrupt or glow plug short circuit

10x Overheating

11x Circulating pump interrupt or circulating pump short

circuit

Thermo 90 S / Thermo 90 ST 3 Function description

305

Page for notes

Thermo 90 S / Thermo 90 ST 4 Technical data

401

4 Technical data

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.

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.

Heater Operation Thermo 90 S

Petrol

Thermo 90 ST

Petrol

Thermo 90 S diesel

Thermo 90 S-ADR

Thermo 90 ST diesel

Thermo 90 ST-ADR

EC licensing symbol ~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

Fuel Petrol Diesel

Fuel consumption Max.

regulating

range

0.25 l/h – 1.0 l/h

1.1 l/h

0.19 l/h – 0.9 l/h

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

pump

(without vehicle fan)

Max.

regulating

range

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

Control unit: - Operation -40 ... +75 °C -40 ... +85 °C -40 ... +75 °C -40 ... +85 °C

- Storage -40 ... +85 °C

Metering pump: - Operation -40 ... +20 °C -40 ... +40 °C

- Storage -40 ... +85 °C

Permitted operating pressure (heat carrier) 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

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

Weight 4.8 kg

4 Technical data Thermo 90 S / Thermo 90 ST

402

Page for notes

Thermo 90 S / Thermo 90 ST 5 Troubleshooting

501

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.

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:

• 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.

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.

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

5 Troubleshooting Thermo 90 S / Thermo 90 ST

502

5.3 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.

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

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

1 Flashing pulse

(start did not occur)

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

2 Flashing pulses

(flame failure during burner

operation)

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

6 Flashing pulses

(temperature sensor

defective)

Cabling Check cabling for damage, discontinuity and

short-circuit

Temperature sensor defective Replace temperature sensor

7 Flashing pulses

(metering pump defective/

(overheating guard circuit

defective)

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

8 Flashing pulses

(combustion air fan

defective)

Cabling Check cabling for damage, discontinuity and

short-circuit

Combustion air fan defective Replace combustion air fan

Thermo 90 S / Thermo 90 ST 5 Troubleshooting

503

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

5.4 Visual check for assessing

the burner

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.

5.4.1 Burner housing

• 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.

Fig. 503 Visual check, burner back wall

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

1 Fuel pipe

2 Round seal

3Flame monitor

4 Insulation

5 Glow plug

6Housing

7Screw

8Bar

9 Start air hole

1

2

3

4

5

6

7

8

9

5 Troubleshooting Thermo 90 S / Thermo 90 ST

504

5.4.2 Back wall with metal evaporator

• The pilot flame outlet opening (Fig. 504) must be clear

otherwise no start will occur.

Remedy

Replace burner

• Cracks, flaking as well as black or other discoloration

of the evaporator do not lead to burner failure and are

not significant.

• 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.

Fig. 504 Visual check, pilot flame outlet opening

5.4.3 Combustion chamber

• The combustion chamber (Fig. 505) should not be

damaged (e.g. dented). A dented combustion

chamber can lead to poor combustion or carbon build-

up in the heater.

Remedy

Replace burner

• 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

5.4.4 Complete burner

• The cables of the glow plug and flame monitor must

be routed as shown in Fig. 503.

• The screw connection of the housing and combustion

chamber (Fig. 505) must be tight.

• 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).

• The round sealing ring (Fig. 503) must evenly

surround the fuel pipe and must not leak.

• 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.

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

Fig. 505 Visual check, complete burner

Pilot flame outlet opening

Metal evaporator, petrol

Pilot flame outlet opening

Metal evaporator, diesel

Combustion chamber Swirl orifice

Air holes

Gap between housing

and combustion chamber

Thermo 90 S / Thermo 90 ST 6 Function tests

601

6 Function tests

6.1 General

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.

6.2 Settings

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

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: 990 ... 1010 Ω

Test current: < 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: 12 volts (red) 24 volts

(green)

Resistance at 25 °C: 0.3 ... 0.6 Ω1.3 ... 1.44 Ω

Test current: < 5 mA < 5 mA

6.3.3 Resistance test on the flame monitor

If you conduct this electrical test with a digital multimeter,

the flame monitor should have the following values:

Cold test:

Resistance at 25 °C: 3.0 ±0.4 Ω

Test current: < 5 mA

Hot test:

Resistance at 800 ±20 °C: 8 ±1.0 Ω

(ceramic rod at red heat over length of approx. 20 mm)

Test current: < 5 mA

6.3.4 Testing the combustion air fan

The motor speed test must be performed with the heater

assembled and in the operating voltage range. Listen out

for grinding noises.

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 (±9%)

Speed in control range max. 5600 rpm (±9%)

Fit a new combustion air fan if the speeds are outside

tolerance (see 9.2.5).

6 Function tests Thermo 90 S / Thermo 90 ST

602

Page for notes

Thermo 90 S / Thermo 90 ST 7 Circuit diagrams

701

7 Circuit diagrams

7.1 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

7 Circuit diagrams Thermo 90 S / Thermo 90 ST

702

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

2

8

11

101

12 74

H3

P2

H1

H6

3085

86 87 87a

K5

br

br

br

rt

br gn/ws

rt/bl

ge

sw

rt

ws/bl

vi

bl

vi/bl

gr

gn

or

or

58

15

12

58

15

F2 F3 X6 F1

bl

br

30

30

31

31

sw

rt

sw

rt

ws

A2

11 6

12

2

2

23

1

0

710

32

1

1

1

4

58

11 9

9

4

3

71568

10

212

M2 M3

M1

br

br

bl

239

8657

112

11 10 4

sw

br

X1

X12 (ST 2)

X3

X5

X13

(ST 3)

X11

(ST 1)

Y1

vi

vi

gr

gr

gn

gn

B3

B4

B1 B2 A1

E

M

M

M

X5 X6

ϑϑ

X13 (ST 3)

1

12

2

11

3

10

4

9

5

8

6

7

X1

1

1

2

2

X11 (ST 1) X12 (ST 2)

ge

B1

B3

B2

E

X1

M1

M2

21

X3

S8

6

9

3

12

1

11

3

9

5

7

1

11

3

9

5

7

1

2

1

2

3

4

Temperature coding (temperature at water outlet):

See table on page 302

Digital timer P2:

with positive at connection 10 = Continuous operation with immediate

heating

Connection 10 open = Variable heating duration can be

programmed = (10 min to 120 min);

= Default setting 120 min

Vehicle fuse

Vehicle fan switch

1

2

3

4

Cable cross-sections

< 7.5 m 7.5 - 15 m

0.75 mm2

1.5 mm2

2.5 mm2

4.0 mm2

1.5 mm2

2.5 mm2

4.0 mm

6.0 mm

1.0 mm2

1.0 mm2

1.0 mm2

0.75 mm2

2

2

Cable colours

bl

br

ge

gn

gr

or

rt

sw

vi

ws

Blue

Brown

Yellow

Green

Grey

Orange

Red

Black

Violet

White

Cable colours

bl

br

ge

gn

gr

or

rt

sw

vi

ws

Blue

Brown

Yellow

Green

Grey

Orange

Red

Black

Violet

White

Item Designation Comment

A1 Heater

A2 Control unit

B1 Flame monitor

B2 Temperature sensor

B3 Temperature limiter/

overheating guard circuit

B4 Cabin thermostat

E Glow plug

F1 20 A fuse Blade-type fuse SAE J 1284

F2 5 A fuse Blade-type fuse SAE J 1284

F3 20 A fuse Blade-type fuse SAE J 1284

H1 “Heating” symbol in the display Operating indicator (in item P2)

H3 Symbol light Light (in item P2)

H6 Red LED Light in immediate heat button, ready

indicator, switch-on indicator

(in item P2)

K5 Relay For vehicle fan

M1 Motor Combustion air fan

Item Designation Comment

M2 Motor Circulating pump

M3 Motor Vehicle fan

P2 Standard clock For programmed operation

S8 Momentary-contact switch Immediate heat button remote

control

X1 12-pin plug connector To item A1

X3 12-pin plug connector To item P2

X5 12-pin plug connector To Y1

X6 12-pin plug connector Diagnosis

X11 12-pin plug connector To item A2 (ST 1)

X12 12-pin plug connector To item A2 (ST 2)

X13 12-pin plug connector To item A2 (ST 3)

Y1 Metering pump Fuel pump for heater

Thermo 90 S / Thermo 90 ST 7 Circuit diagrams

703

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

2

8

11

101

12 74

H3

P2

H1

H6

3030 8585

8686 8787 87a87a

K5K3

br

br

br

rt

rt

br gn/ws

rt/bl

ge

sw

rt

ws/bl

vi

bl

vi/bl

gr

gn

or

or

58

15

12

58

15

F2 F3 X6 F1

bl

br

30

30

31

31

sw

rt

sw

sw

rt

ws

A2

11 6

12

2

2

23

1

0

710

32

1

1

1

4

58

11 9

9

4

3

71568

10

212

M2 M3

M1

br

br

bl

239

8657

112

11 10 4

sw

br

X1

X12 (ST 2)

X3

X5

X13

(ST 3)

X11

(ST 1)

Y1

vi

vi

gr

gr

gn

gn

B3

B4

B1 B2 A1

E

M

M

M

X5 X6

ϑϑ

X13 (ST 3)

1

12

2

11

3

10

4

9

5

8

6

7

X1

1

1

2

2

X11 (ST 1) X12 (ST 2)

ge

B1

B3

B2

E

X1

M1

M2

21

X3

S8

6

9

3

12

1

11

3

9

5

7

1

11

3

9

5

7

1

2

S9

1

2

3

4

Temperature coding (temperature at water outlet):

See table on page 302

Digital timer P2:

with positive at connection 10 = Continuous operation with immediate

heating

Connection 10 open = Variable heating duration can be

programmed = (10 min to 120 min);

= Default setting 120 min

Vehicle fuse

Vehicle fan switch

1

2

3

4

Cable cross-sections

< 7.5 m 7.5 - 15 m

0.75 mm2

1.5 mm2

2.5 mm2

4.0 mm2

1.5 mm2

2.5 mm2

4.0 mm

6.0 mm

1.0 mm2

1.0 mm2

1.0 mm2

0.75 mm2

2

2

Cable colours

bl

br

ge

gn

gr

or

rt

sw

vi

ws

Blue

Brown

Yellow

Green

Grey

Orange

Red

Black

Violet

White

Item Designation Comment

A1 Heater

A2 Control unit

B1 Flame monitor

B2 Temperature sensor

B3 Temperature limiter/

overheating guard circuit

B4 Cabin thermostat

E Glow plug

F1 20 A fuse Blade-type fuse SAE J 1284

F2 5 A fuse Blade-type fuse SAE J 1284

F3 20 A fuse Blade-type fuse SAE J 1284

H1 “Heating” symbol in the display Operating indicator (in item P2)

H3 Symbol light Light (in item P2)

H6 Red LED Light in immediate heat button, ready

indicator, switch-on indicator (in item

P2)

K3 Relay For circulating pump remote control

K5 Relay For vehicle fan

Item Designation Comment

M1 Motor Combustion air fan

M2 Motor Circulating pump

M3 Motor Vehicle fan

P2 Standard clock For programmed operation

S8 Momentary-contact switch Immediate heat button remote

control

S9 Switch Heating/circulating pump remote

control

X1 12-pin plug connector To item A1

X3 12-pin plug connector To item P2

X5 12-pin plug connector To Y1

X6 12-pin plug connector Diagnosis

X11 12-pin plug connector To item A2 (ST 1)

X12 12-pin plug connector To item A2 (ST 2)

X13 12-pin plug connector To item A2 (ST 3)

Y1 Metering pump Fuel pump for heater

7 Circuit diagrams Thermo 90 S / Thermo 90 ST

704

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

Temperature coding (temperature at water outlet):

See table on page 302

Vehicle fuse

Vehicle fan switch

1

3

4

A

FE

B

30

85

86 87 87a

H2

S4

K5

br

br

br

rt

br gn/ws

rt/bl

ge

sw

rt

ws/bl

vi

bl

vi/bl

gr

gn

or

or

58

15

12

D+/61

58

15

D+/61

F2 F3 X6 S7 F1

bl

br

30

31

S5

S5

sw

rt

rt

ws

A2

11 6

12

2

2

23

1

0

710

32

1

1

1

4

58

11 9

9

4

3

71568212

M2 M3

M1

br

br

bl

239

8657

112

11 10 4

sw

br

X1

H5 Y2

Y1

vi

gr

gn

B3

B4

B1 B2 A1

E

M

M

M

ϑϑ

ge

B1

B3

B2

E

X1

M1

M2

sw

10

X12 (ST 2)

X5

X13

(ST 3)

X11

(ST 1)

vi

gr

gn

X5 X6

X13 (ST 3)

1

12

2

11

3

10

4

9

5

8

6

7

X1

1

1

2

2

X11 (ST 1) X12 (ST 2)

21

1

11

3

9

5

7

1

11

3

9

5

7

1

2

1

3

4

Cable cross-sections

< 7.5 m 7.5 - 15 m

0.75 mm2

1.5 mm2

2.5 mm2

4.0 mm2

1.5 mm2

2.5 mm2

4.0 mm

6.0 mm

1.0 mm2

1.0 mm2

1.0 mm2

0.75 mm2

2

2

Cable colours

bl

br

ge

gn

gr

or

rt

sw

vi

ws

Blue

Brown

Yellow

Green

Grey

Orange

Red

Black

Violet

White

Item Designation Comment

A1 Heater

A2 Control unit

B1 Flame monitor

B2 Temperature sensor

B3 Temperature limiter/

overheating guard circuit

B4 Cabin thermostat

E Glow plug

F1 20 A fuse Blade-type fuse SAE J 1284

F2 5 A fuse Blade-type fuse SAE J 1284

F3 20 A fuse Blade-type fuse SAE J 1284

H2 Light max. 2 W Operating indicator (in item S4)

H5 Lamp min. 1.2 W Switch-on indicator pumping device

K5 Relay For vehicle fan

M1 Motor Combustion air fan

M2 Motor Circulating pump

M3 Motor Vehicle fan

S4 Switch ON/OFF

Item Designation Comment

S5 1 or 2-pin disconnecting switch Emergency off switch

electrical or pneumatic

S7 Pumping device switch To positive

X1 12-pin plug connector To item A1

X5 12-pin plug connector To Y1

X6 12-pin plug connector Diagnosis

X11 12-pin plug connector To item A2 (ST 1)

X12 12-pin plug connector To item A2 (ST 2)

X13 12-pin plug connector To item A2 (ST 3)

Y1 Metering pump Fuel pump for heater

Y2 Solenoid valve For pumping device

Thermo 90 S / Thermo 90 ST 7 Circuit diagrams

705

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

Temperature coding (temperature at water outlet):

See table on page 302

Vehicle fuse

Vehicle fan switch

1

3

4

A

FE

B

30

85

86 87 87a

H2

S4

K5

br

br

br

rt

br gn/ws

rt/bl

ge

sw

rt

ws/bl

vi

bl

vi/bl

gr

gn

or

or

58

15

12

D+/61

58

15

D+/61

F2 F3 X6 F1

bl

br

30

31

S5

S5

sw

rt

rt

ws

A2

11 6

12

2

2

23

1

0

710

32

1

1

1

4

58

11 9

9

4

3

71568212

M2 M3

M1

br

br

bl

239

8657

112

11 10 4

sw

br

X1

Y1

vi

gr

gn

B3

B4

B1 B2 A1

E

M

M

M

ϑϑ

ge

B1

B3

B2

E

X1

M1

M2

sw

10

X12 (ST 2)

X5

X13

(ST 3)

X11

(ST 1)

vi

gr

gn

X5 X6

X13 (ST 3)

1

12

2

11

3

10

4

9

5

8

6

7

X1

1

1

2

2

X11 (ST 1) X12 (ST 2)

21

1

11

3

9

5

7

1

11

3

9

5

7

1

2

1

3

4

Cable cross-sections

< 7.5 m 7.5 - 15 m

0.75 mm2

1.5 mm2

2.5 mm2

4.0 mm2

1.5 mm2

2.5 mm2

4.0 mm

6.0 mm

1.0 mm2

1.0 mm2

1.0 mm2

0.75 mm2

2

2

Cable colours

bl

br

ge

gn

gr

or

rt

sw

vi

ws

Blue

Brown

Yellow

Green

Grey

Orange

Red

Black

Violet

White

Item Designation Comment

A1 Heater

A2 Control unit

B1 Flame monitor

B2 Temperature sensor

B3 Temperature limiter/

overheating guard circuit

B4 Cabin thermostat

E Glow plug

F1 20 A fuse Blade-type fuse SAE J 1284

F2 5 A fuse Blade-type fuse SAE J 1284

F3 20 A fuse Blade-type fuse SAE J 1284

H2 Light max. 2 W Operating indicator (in item S4)

K5 Relay For vehicle fan

M1 Motor Combustion air fan

M2 Motor Circulating pump

M3 Motor Vehicle fan

S4 Switch ON/OFF

S5 1 or 2-pin disconnecting switch Emergency off switch

electrical or pneumatic

Item Designation Comment

S7 Pumping device switch To positive

X1 12-pin plug connector To item A1

X5 12-pin plug connector To Y1

X6 12-pin plug connector Diagnosis

X11 12-pin plug connector To item A2 (ST 1)

X12 12-pin plug connector To item A2 (ST 2)

X13 12-pin plug connector To item A2 (ST 3)

Y1 Metering pump Fuel pump for heater

7 Circuit diagrams Thermo 90 S / Thermo 90 ST

706

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

ϑϑ

Temperature coding (temperature at water outlet):

See table on page 302

Digital timer P2:

with positive at connection 10 = Continuous operation with immediate

heating

Connection 10 open = Variable heating duration can be

programmed = (10 min to 120 min);

= Default setting 120 min

Vehicle fuse

Vehicle fan switch

1

2

3

4

Cable cross-sections

< 7.5 m 7.5 - 15 m

0.75 mm2

1.5 mm2

2.5 mm2

4.0 mm2

1.5 mm2

2.5 mm2

4.0 mm

6.0 mm

1.0 mm2

1.0 mm2

1.0 mm2

0.75 mm2

2

2

Cable colours

bl

br

ge

gn

gr

or

rt

sw

vi

ws

Blue

Brown

Yellow

Green

Grey

Orange

Red

Black

Violet

White

Item Designation Comment

A1 Heater

A2 Control unit

B1 Flame monitor

B2 Temperature sensor

B3 Temperature limiter/

overheating guard circuit

B4 Cabin thermostat

E Glow plug

F1 20 A fuse Blade-type fuse SAE J 1284

F2 5 A fuse Blade-type fuse SAE J 1284

F3 20 A fuse Blade-type fuse SAE J 1284

H1 “Heating” symbol in the display Operating indicator (in item P2)

H3 Symbol light Light (in item P2)

H6 Red LED Light in immediate heat button, ready

indicator, switch-on indicator

(in item P2)

K5 Relay For vehicle fan

M1 Motor Combustion air fan

M2 Motor Circulating pump

M3 Motor Vehicle fan

Item Designation Comment

P2 Standard clock For programmed operation

S8 Momentary-contact switch Immediate heat button remote

control

X1 4-pin plug connector To item A2

X2 2-pin plug connector To item A2

X3 2-pin plug connector To item A2

X4 2-pin plug connector To item A2

X5 12-pin plug connector To item A2

X6 12-pin plug connector Diagnosis

X8 12-pin plug connector To item A2 (ST 2)

X9 12-pin plug connector To item P2

X10 2-pin plug connector W-bus diagnosis

X11 12-pin plug connector To Y1

Y1 Metering pump Fuel pump for heater

Thermo 90 S / Thermo 90 ST 7 Circuit diagrams

707

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

ϑϑ

Temperature coding (temperature at water outlet):

See table on page 302

Digital timer P2:

with positive at connection 10 = Continuous operation with immediate

heating

Connection 10 open = Variable heating duration can be

programmed = (10 min to 120 min);

= Default setting 120 min

Vehicle fuse

Vehicle fan switch

1

2

3

4

Cable cross-sections

< 7.5 m 7.5 - 15 m

0.75 mm2

1.5 mm2

2.5 mm2

4.0 mm2

1.5 mm2

2.5 mm2

4.0 mm

6.0 mm

1.0 mm2

1.0 mm2

1.0 mm2

0.75 mm2

2

2

Cable colours

bl

br

ge

gn

gr

or

rt

sw

vi

ws

Blue

Brown

Yellow

Green

Grey

Orange

Red

Black

Violet

White

Item Designation Comment

A1 Heater

A2 Control unit

B1 Flame monitor

B2 Temperature sensor

B3 Temperature limiter/

overheating guard circuit

B4 Cabin thermostat

E Glow plug

F1 20 A fuse Blade-type fuse SAE J 1284

F2 5 A fuse Blade-type fuse SAE J 1284

F3 20 A fuse Blade-type fuse SAE J 1284

H1 “Heating” symbol in the display Operating indicator (in item P2)

H3 Symbol light Light (in item P2)

H6 Red LED Light in immediate heat button, ready

indicator, switch-on indicator

(in item P2)

K3 Relay For circulating pump remote control

K5 Relay For vehicle fan

Item Designation Comment

M1 Motor Combustion air fan

M2 Motor Circulating pump

M3 Motor Vehicle fan

P2 Standard clock For programmed operation

S8 Momentary-contact switch Immediate heat button remote

control

S9 Switch Heating/circulating pump remote

control

X1 4-pin plug connector To item A2

X2 2-pin plug connector To item A2

X3 2-pin plug connector To item A2

X4 2-pin plug connector To item A2

X5 12-pin plug connector To item A2

X6 12-pin plug connector Diagnosis

X8 12-pin plug connector To item A2 (ST 2)

X9 12-pin plug connector To item P2

X10 2-pin plug connector W-bus diagnosis

X11 12-pin plug connector To Y1

Y1 Metering pump Fuel pump for heater

7 Circuit diagrams Thermo 90 S / Thermo 90 ST

708

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

ϑϑ

Temperature coding (temperature at water outlet):

See table on page 302

Vehicle fuse

Vehicle fan switch

1

3

4

Cable cross-sections

< 7.5 m 7.5 - 15 m

0.75 mm2

1.5 mm2

2.5 mm2

4.0 mm2

1.5 mm2

2.5 mm2

4.0 mm

6.0 mm

1.0 mm2

1.0 mm2

1.0 mm2

0.75 mm2

2

2

Cable colours

bl

br

ge

gn

gr

or

rt

sw

vi

ws

Blue

Brown

Yellow

Green

Grey

Orange

Red

Black

Violet

White

Item Designation Comment

A1 Heater

A2 Control unit

B1 Flame monitor

B2 Temperature sensor

B3 Temperature limiter/

overheating guard circuit

B4 Cabin thermostat

E Glow plug

F1 20 A fuse Blade-type fuse SAE J 1284

F2 5 A fuse Blade-type fuse SAE J 1284

F3 20 A fuse Blade-type fuse SAE J 1284

H2 Light max. 2 W Operating indicator (in item S4)

H5 Lamp min. 1.2 W Switch-on indicator pumping device

K5 Relay For vehicle fan

M1 Motor Combustion air fan

M2 Motor Circulating pump

M3 Motor Vehicle fan

S4 Switch ON/OFF

Item Designation Comment

S5 1 or 2-pin disconnecting switch Emergency off switch

electrical or pneumatic

S7 Pumping device switch To positive

S10 Switch Battery switch in positive

X1 4-pin plug connector To item A2

X2 2-pin plug connector To item A2

X3 2-pin plug connector To item A2

X4 2-pin plug connector To item A2

X5 12-pin plug connector To item A2

X6 12-pin plug connector Diagnosis

X8 12-pin plug connector To item A2 (ST 2)

X10 2-pin plug connector W-bus diagnosis

X11 12-pin plug connector To Y1

Y1 Metering pump Fuel pump for heater

Y2 Solenoid valve For pumping device

Thermo 90 S / Thermo 90 ST 7 Circuit diagrams

709

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

Temperature coding (temperature at water outlet):

See table on page 302

Vehicle fuse

Vehicle fan switch

1

3

4

ϑϑ

Cable cross-sections

< 7.5 m 7.5 - 15 m

0.75 mm2

1.5 mm2

2.5 mm2

4.0 mm2

1.5 mm2

2.5 mm2

4.0 mm

6.0 mm

1.0 mm2

1.0 mm2

1.0 mm2

0.75 mm2

2

2

Cable colours

bl

br

ge

gn

gr

or

rt

sw

vi

ws

Blue

Brown

Yellow

Green

Grey

Orange

Red

Black

Violet

White

Item Designation Comment

A1 Heater

A2 Control unit

B1 Flame monitor

B2 Temperature sensor

B3 Temperature limiter/

overheating guard circuit

B4 Cabin thermostat

E Glow plug

F1 20 A fuse Blade-type fuse SAE J 1284

F2 5 A fuse Blade-type fuse SAE J 1284

F3 20 A fuse Blade-type fuse SAE J 1284

H2 Light max. 2 W Operating indicator (in item S4)

K5 Relay For vehicle fan

M1 Motor Combustion air fan

M2 Motor Circulating pump

M3 Motor Vehicle fan

S4 Switch ON/OFF

S5 1 or 2-pin disconnecting switch Emergency off switch

electrical or pneumatic

Item Designation Comment

S10 Switch Battery switch in positive

X1 4-pin plug connector To item A2

X2 2-pin plug connector To item A2

X3 2-pin plug connector To item A2

X4 2-pin plug connector To item A2

X5 12-pin plug connector To item A2

X6 12-pin plug connector Diagnosis

X8 12-pin plug connector To item A2 (ST 2)

X10 2-pin plug connector W-bus diagnosis

X11 12-pin plug connector To Y1

Y1 Metering pump Fuel pump for heater

7 Circuit diagrams Thermo 90 S / Thermo 90 ST

710

Page for notes

Thermo 90 S / Thermo 90 ST 8 Service work

801

8 Service work

8.1 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.

8 Service work Thermo 90 S / Thermo 90 ST

802

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:

• Clean the exterior of the heater (avoid the ingress of

water).

• Check the electrical connections for contact corrosion

and to ensure that they are secure.

• Check the exhaust and combustion air lines for signs

of damage and to ensure that they are clear.

• Check the fuel line and filter for leaks.

• Check the coolant circuit and circulating pump for

leaks.

• Inspect hoses for cracks.

• Replace the fuel filter if there is one.

Thermo 90 S / Thermo 90 ST 8 Service work

803

Fig. 801 Specimen installations for heater in a truck

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

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

7T-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)

Wiring harness

Fuel line

Exhaust line

Coolant circuit

8 Service work Thermo 90 S / Thermo 90 ST

804

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 < 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.

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.

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.

Fig. 802 Fuel supply

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

l1+l

2≤ 10.0 m

l1≤ 1.2 m

l2≤ 8.8 m

Thermo 90 S / Thermo 90 ST 8 Service work

805

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).

Fig. 803 Webasto fuel extractor

NOTE

The fitting must be made from metal!

Fig. 804 Fuel extraction from the plastic tank

(extraction through tank drain screw)

Fig. 805 Fuel extraction from the plastic tank

(extraction through tank fitting)

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.

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.

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.

> 25 mm

25

Hole

pattern

Only use a fuel

extractor with

metal fuel tanks

Sealing ring

Plastic tank

Sealing ring

Tank fitting

Fuel extractor

8 Service work Thermo 90 S / Thermo 90 ST

806

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.

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).

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.

Fig. 807 Pipe/hose connection

to engine

from tank

to metering pump

Correct

Wrong

Clip

Bubble Bubble

Thermo 90 S / Thermo 90 ST 8 Service work

807

8.6.3 Metering pump with damper

The metering pump is a combined delivery, metering and

shut-off system and is subject to certain installation

criteria (Figs. 802 and 808).

12 volts and 24 volts – petrol and diesel DP2

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.

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.

8.6.3.2 Installation and attachment

The metering pump must be secured with a vibration-

damping 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

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.

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).

8 Service work Thermo 90 S / Thermo 90 ST

808

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.

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:

– 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.

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

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. Connect the wiring harness plug to the heater.

6. Put on the top cover cap and lock it in place.

7. Connect the battery.

8. Bleed the fuel supply system.

9. Bleed the coolant circuit.

10°

10°

Discharge direction

almost vertical 90° ±10°

Thermo 90 S / Thermo 90 ST 8 Service work

809

8.7.2 Changing the circulating pump

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.

8.7.3 Changing the temperature limiter

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.

8.8 Start-up

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).

Thermo 90 S / Thermo 90 ST 9Repair

901

9 Repair

9.1 General

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

CAUTION

All seal elements between the dismantled components

must be removed and new ones fitted.

9.1.1.1 Cleaning

• Clean all stripped down components.

9.1.1.2 Visual inspection

• 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.

9Repair Thermo 90 S / Thermo 90 ST

902

9.2 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.

Fig. 901 Electrical connections (Thermo 90 S)

Locking wedge

Locking lug

(12 pcs.)

Upper cover cap

Removing tool

Supplier for removing tool

(Order no. DT RT1)

Compagnie Deutsch GmbH

Fraunhoferstr. 11b

D-82152 Martinsried

Tel. +49 (89) 899 1570

Fax +49 (89) 857 4684

Thermo 90 S / Thermo 90 ST 9Repair

903

9.2.2 Changing the circulating pump

9.2.2.1 Removal

1. Remove the heater (see 8.7.1.1).

2. Disconnect the electrical connections (see 9.2.1.1).

3. Remove the screws (4, Fig. 902).

4. Remove the clip (3) and circulating pump (2).

5. Complete the work on stripped-down components

(see 9.1.1).

9.2.2.2 Installation

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).

Fig. 902 Changing the circulating pump

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 Sealing ring

2 Circulating

pump

3 Clip

4 Screw (2)

1

2

3

4

9Repair Thermo 90 S / Thermo 90 ST

904

9.2.3 Changing the temperature limiter

9.2.3.1 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).

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:

• 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).

9.2.4 Changing the temperature sensor

9.2.4.1 Removal

1. Remove the heater (see 8.7.1.1).

2. Disconnect the electrical connections (see 9.2.1.1).

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 9Repair

905

Fig. 903 Changing the temperature limiter and temperature sensor

6

5

1

2

3

4

1 Protective cap

2 Clip

3 Temperature limiter

4 Heat exchanger

5 Round sealing ring

6 Temperature sensor

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.

9Repair Thermo 90 S / Thermo 90 ST

906

9.2.5 Changing the combustion air fan

9.2.5.1 Removal

1. Remove the heater (see 8.7.1.1).

2. Disconnect the electrical connections (see 9.2.1.1).

3. Remove the screws (2, Fig. 904).

4. Pull the combustion air fan (1) off the burner head (4)

and remove together with the shaped sealing ring (3).

NOTE

Remove the control unit if necessary from 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).

9.2.5.2 Fitting

NOTE

Insert the shaped seal (3, Fig. 904) correctly and grease it

(e.g. with Vaseline). Take care not to squash it.

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

Install the control unit if necessary on the Thermo

90 S/Thermo 90 ST heater with flange-mounted

control unit.

3. Connect the electrical connections (see 9.2.1.2).

4. Install the heater (see 8.7.1.2).

Fig. 904 Changing the combustion air fan

Thermo 90 S

Control unit 1

23

4

1

1 Combustion air

fan

2 Screw (2)

3 Shaped sealing

ring

4 Burner head

Control unit

NOTE

A Thermo 90 ST heater is shown.

Thermo 90 S / Thermo 90 ST 9Repair

907

9.2.6 Changing the burner, flame monitor and

glow plug

9.2.6.1 Removal

1. Remove the heater (see 8.7.1.1).

2. Remove the combustion air fan (see 9.2.5.1).

3. Remove the screw (5, Fig. 905) and washer (4).

4. Remove the nuts (10) and pull off the bar (8).

5. Pull the grommets (11 and 12) out of the slots in the

housing of the combustion pipe (3).

6. Pull the grommet (13) and burner (1) out of the burner

head and remove with the swirl orifice (2).

7. Pull the flame monitor (7) and glow plug (6) from the

burner (1) and remove.

8. Perform a visual check for assessing the burner

(see 5.3).

9. Complete the work on stripped-down components

(see 9.1.1).

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).

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.

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).

Glow plug Flame monitor

9Repair Thermo 90 S / Thermo 90 ST

908

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

1 Burner

2 Swirl orifice

3 Burner head

4 Washer

5Screw

6 Glow plug

7 Flame monitor

8Bar

9 Insulation

10 Nut (2)

11 Grommet

12 Grommet

13 Grommet

NOTE

A Thermo 90 ST heater is shown.

The figure can also be used for the

Thermo 90 S heater.

11

12

6

7

8

9

10

13

1

3

5

4

2

Thermo 90 S / Thermo 90 ST 9Repair

909

9.2.7 Changing the burner head

9.2.7.1 Removal

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).

9.2.7.2 Installation

NOTE

The burner head and exhaust outlet port can also be

aligned during installation in the vehicle.

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).

Fig. 906 Changing the burner head

1 Burner head

2 V-clamping collar

3 Heat exchanger

1

2

3

NOTE

A Thermo 90 ST heater is shown.

The figure can also be used for the

Thermo 90 S heater.

9Repair Thermo 90 S / Thermo 90 ST

910

9.2.8 Changing the heat exchanger

9.2.8.1 Removal

1. Remove the heater (see 8.7.1.1).

2. Remove the circulating pump (see 9.2.2.1).

3. Remove the temperature limiter (see 9.2.3.1).

4. Remove the temperature sensor (see 9.2.4.1).

5. Remove the combustion air fan (see 9.2.5.1).

6. 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).

9.2.8.2 Installation

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).

Thermo 90 S / Thermo 90 ST 10 Packing / Storage / Shipment

1001

10 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.

10 Packing / Storage / Shipment Thermo 90 S / Thermo 90 ST

1002

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