1.1Contents and purpose ........................................................................................................................... 101
1.2Meaning of signal words ........................................................................................................................ 101
1.3Additional documentation to be used..................................................................................................... 101
1.4Safety instructions and regulations........................................................................................................ 101
1.4.1 General safety regulations........................................................................................................... 101
1.6Suggestions for improvements and modifications ................................................................................. 102
2General description
2.1Combustion air fan................................................................................................................................. 202
2.10 Control unit ............................................................................................................................................ 203
3.1Switching on .......................................................................................................................................... 301
3.4Switching off .......................................................................................................................................... 302
3.5Heater functions when installed in ADR vehicles .................................................................................. 302
3.6.2 Diagnosis after fault lock-out, Thermo 90 S and Thermo 90 ST ................................................. 304
4Technical data ................................................................................................................................................ 401
8.2Work on the heater ............................................................................................................................... 801
8.3Work on the vehicle .............................................................................................................................. 801
8.4Heater trial run ...................................................................................................................................... 802
8.5Service work ......................................................................................................................................... 802
8.6Visual 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
8.6.5 Combustion air supply ................................................................................................................ 807
8.6.6 Exhaust line ................................................................................................................................ 808
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
10Packing, storage and shipment
10.1 General ................................................................................................................................................ 1001
III
List of illustrationsThermo 90 S / Thermo 90 ST
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
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
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
IV
Thermo 90 S / Thermo 90 ST1Introduction
1Introduction
1.1Contents 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.
1.2Meaning 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.
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.
NOTE
This heading is used to direct your attention to a special
feature deemed essential to highlight.
1.3Additional 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.
1.4Safety 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 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
1IntroductionThermo 90 S / Thermo 90 ST
1.5Statutory regulations governing
installation
Refer to the installation instructions for the statutory
regulations if necessary.
1.6Suggestions for improvements and
modifications
Complaints, improvement suggestions or corrections
relating to this technical manual should be addressed to:
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.
11
4
3
Thermo 90 S
2
1
7
10 Inlet, combustion air
11 Control unit (can also be
9
10
8
5
6
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
arranged externally in the
vehicle)
Thermo 90 S heater
201
2General descriptionThermo 90 S / Thermo 90 ST
4
3
2
11
1
7
10
9
8
5
6
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
Thermo 90 ST heater
2.1Combustion air fan
The combustion air fan supplies the air required for the
combustion process from the combustion air inlet to the
burner insert.
2.2Heat exchanger
In the heat exchanger, the heat generated by combustion
is transferred to the coolant circuit.
Temperature limiter
Temperature sensor
202
Combustion air fan
Heat exchanger
Thermo 90 S / Thermo 90 ST2General description
2.3Temperature 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.
2.4Temperature 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.
2.5Burner insert
The fuel is distributed over the burner cross-section in the
combustion pipe in the burner insert.
2.6Glow 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.
2.8Combustion pipe
The mixture of fuel and air burns in the combustion pipe,
thus causing the heat exchanger to become hot.
Combustion pipe
2.9Circulating 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
Flame monitor
2.7Flame 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.
Circulating pump
2.10Control 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.
2.11Metering 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
2General descriptionThermo 90 S / Thermo 90 ST
Page for notes
204
Thermo 90 S / Thermo 90 ST3Function description
3Function description
(Fig. 301)
3.1Switching 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.
3.2Heating 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.
3.3Control 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
3Function descriptionThermo 90 S / Thermo 90 ST
A
B
C
D
E
F
G
257
1
0
1
1
/4
0
1
1
/2
1
/4
0
1
0
1
0
1
0
1
0
*
Safety time
181512
986431
3080907570°C
22
212019171614131110
Fig. 301 Sequence of functions
23
* If no flame is formed, the
start is automatically
repeated (20 s pulse preglow, 90 s safety time).
o Possible regulating
❏
temperatures that can be
set, see table below
3.4Switching 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.
3.5Heater functions
when installed in ADR vehicles
Sequence of functions for Thermo 90 S and ST
1
Switch on
2
Component interrogation
3
Pre-glow 40 s (pulsed)
4
Metering pump supply 5 – 7 s (1)
5
Metering pump / part load (1/4)
6
Flame monitor take-over
7
Stabilisation time
8
Full load
9
Vehicle fan “On”
10
Control range
11
Control pause
12
Flame monitor “Cold” (0)
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).
13
Run-on ended
14
Pre-glow 15 – 20 s (pulsed)
15
Metering pump supply 5 – 7 s (1)
16
Metering pump / part load (1/4)
17
Flame monitor take-over
18
Stabilisation time
19
Coolant temperature reduced
20
Full load
21
Switch off (run-on)
22
Flame monitor “Cold” (0)
23
Run-on ended
302
Thermo 90 S / Thermo 90 ST3Function description
AGlow plug
BMetering pump
CCombustion air fan
DFlame monitor
EOperation indicator light
FCirculating pump
GVehicle fan
3.6Malfunctions
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 volts10.5 V - 0.5 V
24 volts21 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
3Function descriptionThermo 90 S / Thermo 90 ST
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 01No start (after 2 attempts to start)
F 02Flame failure
F 03Undervoltage or overvoltage
F 04Premature flame recognition
F 05Flame monitor interrupt or flame monitor short
circuit
F 06Temperature sensor interrupt or temperature
sensor short circuit
F 07Metering pump interrupt or metering pump short
circuit
F 08Fan motor interrupt or fan motor short circuit or
fan motor incorrect speed
F 09Glow plug interrupt or glow plug short circuit
F10 Overheating
F 11Circulating 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
indicator light during the run-on time of the heater.
After five short signals, count the long flashes:
1xNo start (after 2 attempts to start)
2xFlame failure
3xUndervoltage or overvoltage
4xPremature flame recognition
5xFlame monitor interrupt or flame monitor short
circuit
6xTemperature sensor interrupt or temperature
sensor short circuit
7xMetering pump interrupt or metering pump short
circuit
8xFan motor interrupt or fan motor short circuit or fan
motor incorrect speed
9xGlow plug interrupt or glow plug short circuit
10xOverheating
11xCirculating pump interrupt or circulating pump short
circuit
on an operating
304
Thermo 90 S / Thermo 90 ST3Function description
Page for notes
305
Thermo 90 S / Thermo 90 ST4Technical data
4Technical 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.
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.
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
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.
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.
HeaterOperationThermo 90 S
Petrol
EC licensing symbol~S299~S298
ModelWater heater with Ferro-Tec technology
Heat outputMax.
regulating
range
FuelPetrolDiesel
Fuel consumptionMax.
Rated voltage12 volts12 or 24 volts
Operating voltage range10 ... 15 volts10 ... 15 or 20 ... 30 volts
Nominal power consumption with circulating
pump
(without vehicle fan)
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 exchanger0.15 l
Max. combustion air intake temperature+40 °C
Minimum capacity of the circuit6.00 l
Delivery rate of the circulating pump
against 0.15 bar
in exhaust fumes (permitted function
CO
2
range)
adjustment values at approx. +20 °C
CO
2
and geographic altitude above sea level
Heater dimensions (tolerance ± 3 mm)
* Control unit installed on the heater
Weight4.8 kg
regulating
range
Max.
regulating
range
Max.10 ... 12.0% by volume
Max.0 m 500 m 1000 m
L 310 (355*) mm
2.0 kW – 7.6 kW
0.25 l/h – 1.0 l/h
37 W – 83 W
W 131 mm
H 232 mm
Thermo 90 ST
Petrol
10% 10.6% 11.3%
L 307 (352*) mm
W 131 mm
H 232 mm
Thermo 90 S diesel
Thermo 90 S-ADR
1.8 kW – 7.6 kW
0.19 l/h – 0.9 l/h
1650 l/h
L 310 (355*) mm
W 131 mm
H 232 mm
Thermo 90 ST diesel
Thermo 90 ST-ADR
9.1 kW
1.1 l/h
90 W
37 W – 83 W
L 307 (352*) mm
W 131 mm
H 232 mm
401
4Technical dataThermo 90 S / Thermo 90 ST
Page for notes
402
Thermo 90 S / Thermo 90 ST5Troubleshooting
5Troubleshooting
5.1General
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.
5.2General fault indications
The following table (Fig. 501) lists the possible general
fault indications.
Fault indicationPossible causeRemedy
Heater switches off
automatically
No combustion after start and
restart
Flame extinguishes during
operation
Heater overheats due to lack/
loss of coolant
Voltage failure
longer than 20 seconds
Switch off by temperature limiterAfter the unit has cooled down,
No flame recognition on startCheck flame monitor and connections
Fig. 501 General fault indications
Control unit enters fault lock-out status.
Switch the heater off and back on again.
Contact a Webasto service centre if heater
operation does not start again
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
Check fuses, plug connectors and charge
condition of the battery
press the button of the temperature limiter
before switching on or fit a new temperature
limiter
NOTE
In many cases, the burner may be one possible cause.
Perform a visual check in accordance with 5.4.
501
5TroubleshootingThermo 90 S / Thermo 90 ST
5.3Fault 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.
Fault indicationPossible causeRemedy
No functionElectrical cabling,
fuses
Control unit defectiveReplace control unit
1 Flashing pulse
(start did not occur)
2 Flashing pulses
(flame failure during burner
operation)
Fuel systemCheck fuel level
Combustion air/exhaust lineCheck combustion air/exhaust line for
BurnerClean burner and change if necessary
Fuel supplyCheck fuel level
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.
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)
Fig. 502 Fault indications on fault lock-out (page 2 of 2)
5.4Visual 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.
short-circuit
After the unit has cooled down, press the
button of the temperature limiter before
switching on or fit a new temperature limiter
short-circuit
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.
•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.
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 buildup 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.
Metal evaporator, petrol
Pilot flame outlet opening
•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.
Combustion chamber
Swirl orifice
Metal evaporator, diesel
Fig. 504 Visual check, pilot flame outlet opening
504
Air holes
Gap between housing
and combustion chamber
Fig. 505 Visual check, complete burner
Thermo 90 S / Thermo 90 ST6Function tests
6Function tests
6.1General
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.
6.2Settings
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: CO
run for about 5 minutes before measuring).
Rough setting: Screw the adjusting screw fully in
clockwise and then one turn back.
value is reduced (let the heater
2
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%)
6.3Testing 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
Fit a new combustion air fan if the speeds are outside
tolerance (see 9.2.5).
601
6Function testsThermo 90 S / Thermo 90 ST
Page for notes
602
Thermo 90 S / Thermo 90 ST7Circuit diagrams
7Circuit diagrams
7.1General
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
7Circuit diagramsThermo 90 S / Thermo 90 ST
58
15
30
M1
P2
31
H3
B1
E
B2
2
101
H1
12
4
7
S8
br
B3
X1
M2
X1
11221131049586
X3
3
6
7
9
12
F2F3
H6
rt
11
2
8
sw
ws
X12 (ST 2)
3
4
11
9
10
X3
X11
(ST 1)
rt
1458
ge
br
112
ge
E
X5
21
122
X6
9
12
rt
br
bl
br
sw
8657
br
ws/bl
br
bl
sw
M
M
M2M3M1
X6
2
1
12
32
116
X11 (ST 1)X12 (ST 2)
11
9
7
5
3
1
710
(ST 3)
vi
239
gr
vi/bl
11104
vi
vi
B3
gr
B1B2
or
or
gn
X1
gr
ϑϑ
gn
gn
A1
1
71568
X13
Y1
X13 (ST 3)
11
9
7
5
3
1
F1
B4
212
gn/ws
A2
2
1
rt/bl
1
58
15
30
3
rt
86 87
br
bl
K5
87a
3085
sw
4
X5
2
1
br
M
3
0
1
2
31
Temperature coding (temperature at water outlet):
1
See table on page 302
Digital timer P2:
2
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
3
Vehicle fan switch
4
ItemDesignationComment
A1Heater
A2Control unit
B1Flame monitor
B2Temperature sensor
B3Temperature limiter/
overheating guard circuit
B4Cabin thermostat
EGlow plug
F120 A fuseBlade-type fuse SAE J 1284
F25 A fuseBlade-type fuse SAE J 1284
F320 A fuseBlade-type fuse SAE J 1284
H1“Heating” symbol in the display Operating indicator (in item P2)
H3Symbol lightLight (in item P2)
H6Red LEDLight in immediate heat button, ready
indicator, switch-on indicator
(in item P2)
K5RelayFor vehicle fan
M1MotorCombustion air fan
Fig. 701 System circuit for Thermo 90 S, 12 and 24 V, with standard clock
Thermo 90 S / Thermo 90 ST7Circuit diagrams
58
15
30
M1
P2
31
H3
B1
E
B2
2
101
H1
12
4
7
S8
br
B3
X1
M2
X1
11221131049586
X3
3
6
7
9
12
F2F3
rt
11
2
sw
8
ws
S9
X12 (ST 2)
3
4
H6
X3
rt
rt
11
9
10
br
X11
(ST 1)
1458
ge
sw
112
ge
E
X5
21
122
X6
9
12
sw
br
rt
8657
br
br
ws/bl
br
bl
sw
M
M
M2M3M1
X6
2
1
12
32
116
X11 (ST 1)X12 (ST 2)
11
9
7
5
3
1
710
(ST 3)
viblvi/bl
11104
239
vi
B3
gr
vi
gr
B1B2
or
gn
or
X1
gn
gn
gr
ϑϑ
A1
1
71568
X13
Y1
X13 (ST 3)
11
9
7
5
3
1
F1
B4
212
gn/ws
A2
2
1
rt/bl
1
58
15
30
3
rt
86868787
bl
br
K5K3
87a87a
30308585
sw
4
X5
2
1
br
M
3
0
1
2
31
Temperature coding (temperature at water outlet):
1
See table on page 302
Digital timer P2:
2
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
3
4
Vehicle fan switch
ItemDesignationComment
A1Heater
A2Control unit
B1Flame monitor
B2Temperature sensor
B3Temperature limiter/
overheating guard circuit
B4Cabin thermostat
EGlow plug
F120 A fuseBlade-type fuse SAE J 1284
F25 A fuseBlade-type fuse SAE J 1284
F320 A fuseBlade-type fuse SAE J 1284
H1“Heating” symbol in the display Operating indicator (in item P2)
H3Symbol lightLight (in item P2)
H6Red LEDLight in immediate heat button, ready
indicator, switch-on indicator (in item
P2)
K3RelayFor circulating pump remote control
K5RelayFor vehicle fan
Cable cross-sections
mm
2
2
2
2
2
2
7.5 - 15 m
1.0 mm
1.0 mm
1.5 mm
2.5 mm
4.0 mm
6.0 mm
< 7.5 m
0.75
0.75 mm
1.0 mm
1.5 mm
2.5 mm
4.0 mm
2
2
2
2
2
2
Cable colours
bl
br
ge
gn
gr
or
rt
sw
vi
ws
Blue
Brown
Yellow
Green
Grey
Orange
Red
Black
Violet
White
ItemDesignationComment
M1MotorCombustion air fan
M2MotorCirculating pump
M3MotorVehicle fan
P2Standard clockFor programmed operation
S8Momentary-contact switchImmediate heat button remote
Blue
Brown
Yellow
Green
Grey
Orange
Red
Black
Violet
White
Fig. 704 System circuit for Thermo 90 S-ADR, 24 V, with switch without power take-off
705
7Circuit diagramsThermo 90 S / Thermo 90 ST
Temperature coding (temperature at water outlet):
1
See table on page 302
Digital timer P2:
2
with positive at connection 10= Continuous operation with immediate
heating
Connection 10 open= Variable heating duration can be
programmed= (10 min to 120 min);
Vehicle fuse
3
4
Vehicle fan switch
ItemDesignationComment
A1Heater
A2Control unit
B1Flame monitor
B2Temperature sensor
B3Temperature limiter/
overheating guard circuit
B4Cabin thermostat
EGlow plug
F120 A fuseBlade-type fuse SAE J 1284
F25 A fuseBlade-type fuse SAE J 1284
F320 A fuseBlade-type fuse SAE J 1284
H1“Heating” symbol in the display Operating indicator (in item P2)
H3Symbol lightLight (in item P2)
H6Red LEDLight in immediate heat button, ready
K5RelayFor vehicle fan
M1MotorCombustion air fan
M2MotorCirculating pump
M3MotorVehicle fan
Blue
Brown
Yellow
Green
Grey
Orange
Red
Black
Violet
White
706
Fig. 705 System circuit for Thermo 90 ST, 12 and 24 V, with standard clock
Thermo 90 S / Thermo 90 ST7Circuit diagrams
Temperature coding (temperature at water outlet):
1
See table on page 302
Digital timer P2:
2
with positive at connection 10 = Continuous operation with immediate
heating
Connection 10 open= Variable heating duration can be
programmed= (10 min to 120 min);
Vehicle fuse
3
4
Vehicle fan switch
ItemDesignationComment
A1Heater
A2Control unit
B1Flame monitor
B2Temperature sensor
B3Temperature limiter/
overheating guard circuit
B4Cabin thermostat
EGlow plug
F120 A fuseBlade-type fuse SAE J 1284
F25 A fuseBlade-type fuse SAE J 1284
F320 A fuseBlade-type fuse SAE J 1284
H1“Heating” symbol in the display Operating indicator (in item P2)
H3Symbol lightLight (in item P2)
H6Red LEDLight in immediate heat button, ready
K3RelayFor circulating pump remote control
K5RelayFor vehicle fan
= Default setting 120 min
indicator, switch-on indicator
(in item P2)
ϑϑ
control
control
Cable colours
bl
br
ge
gn
gr
or
rt
sw
vi
ws
Blue
Brown
Yellow
Green
Grey
Orange
Red
Black
Violet
White
Cable cross-sections
mm
2
2
2
2
2
2
7.5 - 15 m
1.0 mm
1.0 mm
1.5 mm
2.5 mm
4.0 mm
6.0 mm
2
2
2
2
2
2
< 7.5 m
0.75
0.75 mm
1.0 mm
1.5 mm
2.5 mm
4.0 mm
ItemDesignationComment
M1MotorCombustion air fan
M2MotorCirculating pump
M3MotorVehicle fan
P2Standard clockFor programmed operation
S8Momentary-contact switchImmediate heat button remote
Blue
Brown
Yellow
Green
Grey
Orange
Red
Black
Violet
White
Fig. 708 System circuit for Thermo 90 ST-ADR, 24 V, with switch without power take-off
709
7Circuit diagramsThermo 90 S / Thermo 90 ST
Page for notes
710
Thermo 90 S / Thermo 90 ST8Service work
8Service work
8.1General
This section describes the service work that can be
carried out on the heater when it is installed.
8.2Work 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.
8.3Work 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
8Service workThermo 90 S / Thermo 90 ST
8.4Heater 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.
8.5Service 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.
802
Thermo 90 S / Thermo 90 ST8Service work
NOTE
The Thermo 90 S and Thermo 90 ST
heater is supplied with the control
unit mounted on the combustion air
fan.
Wiring harness
Fuel line
Exhaust line
Coolant circuit
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
Thermo 90 S)
in
Fig. 801 Specimen installations for heater in a truck
803
8Service workThermo 90 S / Thermo 90 ST
8.6Visual 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
rising if possible.
Hose connections must be supported by hose clips to
prevent them slipping.
and (to ensure perfect bleeding)
Permissible fuel inflow
height H (m)
0.000.20
1.000.11
2.000.03
Maximum fuel intake
height S (m)
0.00-0.10
0.50-0.06
1.00-0.02
Only for ADR:
européen relatif au transport international des
marchandises dangereuses par route) governing fuel
tanks, part 9 para. 9.2.4.7, must be adhered to.
A sign must be affixed to the fuel filler neck warning that
the heater must be switched off before refuelling.
The statutory regulation of ADR (Accord
At max. pressure (bar) in
fuel line
At max. negative pressure
(bar) in fuel tank
NOTE
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
l
l
1
2
≤ 1.2 m
≤ 8.8 m
804
Fig. 802 Fuel supply
Thermo 90 S / Thermo 90 ST8Service 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
Hole
pattern
Fig. 803 Webasto fuel extractor
The fitting must be made from metal!
25
> 25 mm
NOTE
Only use a fuel
extractor with
metal fuel tanks
Tank fitting
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
Plastic tank
Sealing ring
Fig. 804 Fuel extraction from the plastic tank
(extraction through tank drain screw)
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
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.
(Fig. 806). The
805
8Service workThermo 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.
to engine
from tank
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
BubbleBubble
Fig. 807 Pipe/hose connection
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
Thermo 90 S / Thermo 90 ST8Service work
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
8.6.3.2 Installation and attachment
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
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.
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 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 cm
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).
2
is required
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
8Service workThermo 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.
Discharge direction
almost vertical 90° ±10°
10°
10°
–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.
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:
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.
The statutory regulation of ADR (Accord
8.7Removal and installation
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.
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
Thermo 90 S / Thermo 90 ST8Service work
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.
8.8Start-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).
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 ST9Repair
9Repair
9.1General
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.
901
9RepairThermo 90 S / Thermo 90 ST
9.2Dismantling 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.
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).
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.
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).
1Sealing ring
2Circulating
pump
3Clip
4Screw (2)
1
2
3
4
Fig. 902 Changing the circulating pump
903
9RepairThermo 90 S / Thermo 90 ST
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.
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).
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).
904
Thermo 90 S / Thermo 90 ST9Repair
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
1Protective cap
2Clip
3Temperature limiter
4Heat exchanger
5Round sealing ring
6Temperature sensor
2
3
6
4
5
Fig. 903 Changing the temperature limiter and temperature sensor
905
9RepairThermo 90 S / Thermo 90 ST
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 flangemounted control unit.
5. Complete the work on stripped-down components
(see 9.1.1).
Thermo 90 S
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).
Control unit
1Combustion air
fan
2Screw (2)
3Shaped sealing
ring
4Burner head
1
2
3
4
Control unit
906
1
A Thermo 90 ST heater is shown.
Fig. 904 Changing the combustion air fan
NOTE
Thermo 90 S / Thermo 90 ST9Repair
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.
Glow plug
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).
Flame monitor
907
9RepairThermo 90 S / Thermo 90 ST
1 Burner
NOTE
A Thermo 90 ST heater is shown.
The figure can also be used for the
Thermo 90 S heater.
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
10Packing / Storage / ShipmentThermo 90 S / Thermo 90 ST
Page for notes
1002
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