– Improper installation or repair of Webasto heating and cooling systems can cause
fire or the leakage of deadly carbon monoxide leading to serious injury or death.
– Installation and repair of Webasto heating and cooling systems requires special
Webasto training, technical information, special tools and special equipment.
– NEVER attempt to install or repair a Webasto heating or cooling system unless you
have successfully completed the factory training course and have the technical skills,
technical information, tools and equipment required to properly complete the
necessary procedures.
– ALWAYS carefully follow Webasto installation and repair instructions and heed all
WARNINGS.
– Webasto rejects any liability for problems and damage caused by the system being
This repair shop manual is intended to assist trained
personnel with repairing both the gasoline and the diesel
versions of the Thermo 90 ST water heaters.
1.2MEANINGOF SIGNAL WORDS
Throughout this manual, the signal words DANGER,
WARNING, CAUTION, and NOTE have the following
meanings:
DANGER: This heading and text style is
used to highlight that non-compliance with
instructions or procedures will cause
injuries or lethal accidents to personnel.
WARNING: This heading and text style is
used to highlight that non-compliance with
instructions or procedures may cause
injuries or lethal accidents to personnel.
CAUTION: This heading and text style is
used to highlight that non-compliance with
instructions or procedures may cause
damage to equipment.
NOTE: This heading and text style is used to
highlight and draw attention to information we
feel you would like to have. It could have to do
with procedures and tips that will help you work
more efficiently.
1.3ADDITIONAL DOCUMENTATION
1.4.1GENERAL 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 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 liters (6.34 quarts).
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 (104 °F) 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.
WARNING: The heater must be switched
off at filling stations and fuel tank farms
because of the risk of explosion.
CAUTION: Wherever inflammable vapors
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.
This workshop manual contains all the information and
instructions required for repairing 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.
1.4SAFETY INFORMATIONAND 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.
www.webasto.us1Webasto Product N.A., Inc.
A temperature of 85 °C (185 °F) (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.
Page 8
INTRODUCTIONTHERMO 90 ST
1.5SUGGESTIONSFOR IMPROVEMENTSAND
C
HANGES
Complaints, improvement suggestions or corrections
relating to this workshop manual should be addressed
to:
Webasto Product North America, Inc.
Technical Documentation Group
15083 North Road
Fenton MI 48430
Phone: 810.593.6000
PC-Fax: 810.593.6135
Webasto Product N.A., Inc.2www.techwebasto.com
Page 9
THERMO 90 STGENERAL DESCRIPTION
2.GENERAL DESCRIPTION
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
2.0 to 7.6 kW in gasoline 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.
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 pin
– a temperature sensor
– a temperature limiter
inside it.
The Thermo 90 ST heater is delivered with the control
unit already flange-mounted on the combustion air fan.
The fuel supply is provided from an external source using
a metering pump.
1
2
11
Figure 1:Thermo 90 ST heater
10
3
4
5
6
1Combustion air fan
2Fuel connection
3Temperature sensor
4Temperature limiter
5Heat exchanger
6Inlet, coolant
7Circulating pump
8Outlet, coolant
9
8
7
9Outlet, exhaust gas
10 Inlet, combustion air
11 Control unit
www.webasto.us3Webasto Product N.A., Inc.
Page 10
GENERAL DESCRIPTIONTHERMO 90 ST
Flame Monitor
Burner Insert
Glow Pin
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.
Figure 2:Combustion air fan
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 overheat guard circuit (bimetallic) protects the heater
against impermissibly high operating temperatures.
The overheat guard circuit trips if the heat exchanger
temperature exceeds 127 ±7 °C (260.6 ±10 °F) and
switches off the heater. This is a self resetting switch.
2.5BURNER INSERT
The fuel is distributed over the burner cross-section in the
combustion pipe in the burner insert.
2.6GLOW PIN
The mixture of fuel and air is ignited by the glow pin
when the heater is started. The glow pin takes the form
of an electrical resistor and is positioned in the burner
insert on the side away from the flame.
2.2HEAT EXCHANGER
In the heat exchanger, the heat generated by
combustion is transferred to the coolant circuit.
Temperature Limiter
Temperature Sensor
Figure 4:Burner Assembly
2.7FLAME MONITOR
Figure 3:Heat exchanger
Webasto Product N.A., Inc.4www.techwebasto.com
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.
Page 11
THERMO 90 STGENERAL DESCRIPTION
0°
0-90°0-90°
2.8COMBUSTION PIPE
The mixture of fuel and air burns in the combustion pipe,
thus causing the heat exchanger to become hot.
Figure 5:Combustion pipe
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.
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).
Figure 7:Control unit - flange mounted
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.
Figure 6:Circulating pump
www.webasto.us5Webasto Product N.A., Inc.
Figure 8:Fuel metering pump
Page 12
GENERAL DESCRIPTIONTHERMO 90 ST
This page for your notes.
Webasto Product N.A., Inc.6www.techwebasto.com
Page 13
THERMO 90 STFUNCTIONAL DESCRIPTION
3.FUNCTIONAL DESCRIPTION
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 pin 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
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.
Gasoline Heaters
The maximum heating power in gasoline heaters is
always 7.6 kW.
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 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.
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.
www.webasto.us7Webasto Product N.A., Inc.
Page 14
FUNCTIONAL DESCRIPTIONTHERMO 90 ST
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
*
3080907570°C
23
22
2120
191716
14
13
1110
181512
986431
25 7
Safety time
*If no flame is formed,
the start is automatically
repeated (20 s pulse preglow, 90 s safety time).
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Figure 9:Sequence of functions
Sequence of functions for Thermo 90 ST
A. Glow pin
B. Metering pump
C. Combustion air fan
D. Flame monitor
E. Operation indicator light
F. Circulating pump
G. Vehicle fan
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
Stabilization time
Full load
Vehicle fan “On”
Control range
Control pause
Flame monitor “Cold” (0)
Webasto Product N.A., Inc.8www.techwebasto.com
Run-on ended (cool-down)
Pre-glow 15 – 20 s (pulsed)
Metering pump supply 5 – 7 s (1)
Metering pump / part load (1/4)
Flame monitor take-over
Stabilization time
Coolant temperature reduced
Full load
Switch off (run-on)
Flame monitor “Cold” (0)
Run-on ended (cool-down)
Page 15
THERMO 90 STFUNCTIONAL DESCRIPTION
3.5MALFUNCTIONS
3.5.1FAULT 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 temperature limiter will reset itself after cool down
period.
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 under voltage protection switches off the system
for longer than 20 seconds, the fuel supply is interrupted
and the heater is shut off. (see table below).
Thermo 90 ST
12 volts10.5 V - 0.5 V
24 volts21 V -1 V
CAUTION: A forced reset of the return
spring when hot can result in damage to
the component.
F11Circulating pump interrupt or circulating
pump short circuit
3.5.2.2 VERSIONWITH 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:
1xNo start (after 2 attempts to start)
2xFlame failure
3xUnder voltage or over voltage
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 pin interrupt or glow pin short circuit
10xOverheating
11xCirculating pump interrupt or circulating
pump short circuit
3.5.2DIAGNOSISAFTER FAULT LOCK-OUT
Check the fuses and plug connectors.
3.5.2.1 VERSIONWITH DIGITAL TIMER
If the system is equipped with a standard timer, a fault
message appears on the display of the digital timer after
a fault occurs:
F01No start (after 2 attempts to start)
F02Flame failure
F03Under voltage or over voltage
F04Premature flame recognition
F05Flame monitor interrupt or flame monitor
short circuit
F06Temperature sensor interrupt or temperature
sensor short circuit
F07Metering pump interrupt or metering pump
short circuit
F08Fan motor interrupt or fan motor short circuit
or fan motor incorrect speed
F09Glow pin interrupt or glow pin short circuit
F10Overheating
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Page 16
FUNCTIONAL DESCRIPTIONTHERMO 90 ST
This page for your notes.
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Page 17
THERMO 90 STTECHNICAL DATA
4.TECHNICAL DATA
Except where limit values are specified, the technical data
listed in the table refer to the usual heater tolerances of
±10% at an ambient temperature of +20 °C (+68 °F) and
at the rated voltage and in rated conditions.
Electrical components:
The control unit, motors for combustion air fan and
circulating pump, ceramic glow pin, metering pump,
timer, and switch are designed for 12 V or 24 V.
The temperature limiter, temperature sensor and flame
monitor are identical on 12 V and 24 V heaters.
range
Rated Voltage12 V12 V24 V
Operating Voltage RangeV10 – 15 V10 – 15 V20 – 30 V
Nominal power consumption with
circulating pump
Max. ambient temperature:
Heater:- Operation
- Storage
Control unit:- Operation
- Storage
Metering pump:- Operation-40... +20 °C (-40... +68 °F)-40... +40 °C (-40... +104 °F)
- Storage-40... +85 °C (-40... +185 °F)
Permitted operating pressure Maximum2.0 bar (29 PSI)
Capacity of the heat exchanger0.15 liters (0.16 quarts)
Max. Combustion Air Inlet Temperature+40 °C (104 °F)
Minimum capacity of the circuit6.0 liters (6.34 quarts)
Delivery rate of the circulating pump
against 0.15 bar
Boost max.
Regulating
range
Fuel for Thermo 90 ST B (gasoline):
The fuel specified by the manufacturer must be used.
Fuel for Thermo 90 ST D (diesel/PME):
The diesel fuel specified by the vehicle 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
system is filled with the new fuel.
The Thermo 90 ST D heater is also licensed for use with
PME (bio-diesel), which complies with ASTM D6751 and
DIN EN 14214.
N/A
2.0 kW – 7.6 kW
(6830 – 25955 BTU/h)
N/A
0.25 l/h – 1.0 l/h
(0.066 g/h – 0.264 g/h)
N/A
37 W – 83 W
-40... +110 °C (90 °C with control unit installed on heater)
-40... +230 °F (194 °F with control unit installed on heater)
-40... +110 °C (90 °C with control unit installed on heater)
-40... +230 °F (194 °F with control unit installed on heater)
-40... +85 °C (-40... +185 °F)
-40... +85 °C (-40... +185 °F)
1650 l/h (435.8 g/h)
9.1 kW (31078 BTU/h)
1.8 kW – 7.6 kW
(6147 – 25955 BTU/h)
Kerosene
1.1 l/h (0.29 g/h)
0.19 l/h – 0.9 l/h
(0.05 g/h – 0.24 g/h)
90 W
37 W – 83 W
www.webasto.us11Webasto Product N.A., Inc.
Page 1 of 2
Page 18
TECHNICAL DATATHERMO 90 ST
HEATEROperationTHERMO 90 ST BTHERMO 90 ST D
CO
In Exhaust Gas
2
(permitted function range)
adjustment values at approx. +20 °C
CO
2
and geographic altitude above sea level
Heater dimensions
(* Control unit installed on the heater)
Weight Of Heater4.8 kg (10.6 lb)
Table 1. Technical data (page 2 of 2)
Maximum10... 12.0% by volume
Maximum0 m (0 ft) 500 m (1640 ft) 1000 m (3280 ft)
10% 10.6% 11.3%
tolerance ±
3 mm
(± 0.12 in)
L 307 mm (352* mm) [12.08 in (13.85 in*)]
W 131 mm (5.15 in)
H 232 mm (9.13 in)
Webasto Product N.A., Inc.12www.techwebasto.com
Page 19
THERMO 90 STTROUBLESHOOTING
5.TROUBLESHOOTING
5.1GENERAL
This section describes how to identify and remedy faults
on the Thermo 90 ST air heater.
If a fault occurs, an error code will be output in the
display of the timer. If the heater has a switch, the ON
control light will flash. In addition, the heater can be
checked using a personal computer (see PC heater
diagnostic operating manual).
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 localization 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 lists the possible general fault
indications.
Fault IndicationPossible CauseRemedy
Heater switches off
automatically
Table 2. General fault indicationsNOTE: In many cases, the burner may be one
No combustion after start and restart
Flame extinguishes during operation
Heater overheats due to lack or loss of
coolant
Voltage failure longer than 20 seconds
Switch off by temperature limiter
No flame recognition on start
possible cause. Perform a visual check in
accordance with 5.4
Control unit enters fault lock-out status.
Switch heater off and then on again.
Contact a Webasto service facility if
heater operation does not start again.
Top up coolant.
After the unit has cooled down, press the
button on the temperature limiter to
reset it before switching on or fit a new
temperature limiter.
Check fuses, plug connectors and charge
condition of battery
After the unit has cooled down, the
temperature limiter will automatically
reset itself.
Check flame monitor and connections
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Page 20
TROUBLESHOOTINGTHERMO 90 ST
5.3FAULT INDICATIONSON 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-down
time of the heater.
Fault indicationPossible causeRemedy
After five short signals, count the long flashes.
In the Thermo 90 ST heater with a standard timer, the
fault is output on the timer display (see 3.5.2). The
following table can be used accordingly.
No functionElectrical cabling, fuses
Control unit defective
1Flashing pulse
(start did not occur)
2Flashing pulses
(flame failure during burner
operation)
3Flashing pulses
(under voltage)
4Flashing pulses
(flame monitor continuously
hot)
Fuel system
Combustion air/exhaust line
Burner
Fuel supply
Burner
Electrical power supplyCheck battery
Flame monitor defectiveReplace flame monitor
Check fuses
Check battery connections:
+ on 12 / – on 9 / + on 3, plug X8
Replace control unit
Check fuel level
Check fuel filter
Bleed fuel system
Check combustion air/exhaust line for foreign
bodies and clean if necessary
Clean burner and change if necessary
Check fuel level
Check fuel filter
Bleed fuel system
Clean burner and change if necessary
Check electrical connections
5Flashing pulses
(flame monitor defective)
6Flashing pulses
(temperature sensor
defective)
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Cabling
Flame monitor defective
Cabling
Temperature sensor defective
Check cabling for damage, discontinuity and
short-circuit
Replace flame monitor
Check cabling for damage, discontinuity and
short-circuit
Heater overheatsCheck coolant and top up if necessary.
Cabling
Check coolant level
Bleed coolant circuit
Check cabling for damage, discontinuity and
short-circuit
Replace metering pump
Check cabling for damage, discontinuity and
short-circuit
Replace combustion air fan
Check cabling for damage, discontinuity and
short-circuit
Replace glow pin
After the unit has cooled down, the
temperature limiter will aut
itself.
Check cabling for damage, discontinuity and
short-circuit
Omatically reset
Circulating pump defective
Table 3. Fault indications on fault lock-out
(Page 2 of 2)
5.3.1PERMANENT HEATER FAULT LOCK-OUT
A permanent fault lock-out is indicated by five short flash
pulses with no long flash pulses following.
Failure
F 01 No start / no flame formation
F 03 Under voltage or over voltage
F 04 Premature flame detection
F 05 Flame monitor
F 06 Temperature sensor
F 07 Fuel pump
F 08 Fan motor
F 09 Ceramic glow pin
F 10 Overheat condition
F 11 Coolant circulating pump
F 02 Flame failureAfter 6
Consecutive number of failed start
attempts
consecutive attempts, of any
After 3
one of the listed fault indicators, the
heater and control unit are locked out
with no further start attempts
possible.
consecutive attempts, heater
and control unit are locked out.
Replace circulating pump
NOTE: The permanent fault lock-out serves as
a safety feature for the customer.
Remedy
See appropriate fault indication in
Table 3.
After eliminating the cause of a heater
fault lock-out, remove main fuse, wait
seconds and reinsert fuse.
Switch heater on.
Contact a Webasto service facility if
heater operation cannot be restored.
Table 4. Permanent heater fault lock-out
www.webasto.us15Webasto Product N.A., Inc.
Page 22
TROUBLESHOOTINGTHERMO 90 ST
5.4VISUAL CHECKFOR ASSESSINGTHE 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.
5.4.1BURNERHOUSING
•The start air hole (item 9, Fig. 10) must be clear
otherwise no start will occur.
Remedy
Carefully remove impurities from the start air hole (e.g.
using a 1.5 mm or 1/16 in. diameter wire). Remove the
glow pin first.
1
1 Fuel pipe
2 Round seal
9
8
7
6
5
4
2
3
3 Flame monitor
4 Insulation
5 Glow pin
6 Housing
7 Screw
8 Bar
9 Start air hole
Figure 10: Visual check, burner back wall
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Page 23
THERMO 90 STTROUBLESHOOTING
Air swirl plate
Air holes
Gap between housing
and combustion chamber
Combustion chamber
5.4.2BACKWALLWITHMETALEVAPORATOR
The pilot flame outlet opening (Fig. 11) 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
Metal evaporator, gasoline
Pilot flame outlet opening
5.4.3COMBUSTIONCHAMBER
•The combustion chamber (Fig. 12) 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. 12) 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
5.4.4COMPLETEBURNER
•The cables of the glow pin and flame monitor must
be routed as shown in Fig. 10.
•The screw connection of the housing and
combustion chamber (Fig. 12) must be tight.
•The housing and the combustion chamber (Fig. 12)
must be firmly connected together and there must
not be any play (check by moving the fuel pipe
slightly).
•The round sealing ring (item 2, Fig. 10) 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. 12) does not have to be even all the way
around.
•The insulation (item 4, Fig. 10) must not be missing.
Metal evaporator, diesel
Figure 11: Visual check, pilot flame outlet opening
www.webasto.us17Webasto Product N.A., Inc.
Figure 12: Visual check, complete burner
Page 24
TROUBLESHOOTINGTHERMO 90 ST
This page for your notes.
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Page 25
THERMO 90 STFUNCTIONAL TESTS
6.FUNCTIONAL TESTS
6.1GENERAL
This section describes the tests conducted on the heater
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
6.2.1SETTINGTHE 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
6.3.2 RESISTANCE TESTOFTHE CERAMIC GLOW PIN
If you conduct this electrical test with a digital
multimeter, the glow pin should have the following
values:
Glow pin:12 V (red)24 V (green)
Resistance at 25 °C :0.3 ... 0.6 1.3 ... 1.44
Resistance at 77 °F :0.3 ... 0.6 1.3 ... 1.44
Test current:< 5 mA< 5 mA
6.3.3RESISTANCE TESTONTHE FLAME MONITOR
If you conduct this test with a digital multimeter, the
flame monitor must have the following values:
Cold Testing:
Resistance at 25 °C (77 °F):3.0 ± 0.4
Test current:< 5mA
Hot Testing:
Resistance at 800 ± 20 °C:8 ± 1.0
Resistance at 1472 ± 36 °F:8 ± 1.0
(ceramic rod at red heat over length of approx. 20 mm)
Test current:< 5 mA
CAUTION: .The CO
instruments must be calibrated.
measuring
2
6.3TESTING INDIVIDUAL COMPONENTS
6.3.1RESISTANCE TESTOFTHE TEMPERATURE
ENSOR
S
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
Test current:< 1 mA
6.3.4TESTINGTHE 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. Install 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%)
Install a new combustion air fan if the speeds are outside
tolerance (see 9.2.4).
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Page 26
FUNCTIONAL TESTSTHERMO 90 ST
This page for your notes.
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Page 27
THERMO 90 STCIRCUIT DIAGRAMS
7.CIRCUIT DIAGRAMS
7.1GENERAL
The circuit diagrams (Figs. 13 and 14) show the possible
circuits for the Thermo 90 ST heater with
– Standard switch
– Standard timer
7.2THERMO 90 ST CIRCUIT DIAGRAM LEGEND
Digital timer P2:
Connection X14 to Red jumper of switch harness results
in continuous operation with immediate heating
(recommended for trucks requiring sleeper heating)
Connection X14 to vehicle ignition connection results in
variable heating duration that can be programmed
(10 min. to 120 min.); default setting 120 min. when
ignition key is switched off. (Recommended for School
bus, Coach and Transit vehicles.)
Optional connection to vehicle instrumentation
panel lighting circuit.
ItemDesignationComment
H3Symbol lightLight (in item P2)
H6Red LEDImmediate heat
button light, ready
indicator, switch-on
control (in item P2)
K1RelayVehicle fan interface
harness option
M1MotorCombustion air fan
M2MotorCirculating pump
P2Digital timer 1531For programmed
operation
S1Toggle switchON/OFF
X1Plug connector, 4-pinTo item A2
X2Plug connector, 2-pinTo item A2
X3Plug connector, 2-pinTo item A2
X4Plug connector, 2-pinTo item A2
X5Plug connector, 2-pinTo item A2
X6Plug connector, 2-pinTo item A2
The following Table applies to Figures 13 and 14.
ItemDesignationComment
A1Heater
A2Control module
B1Flame sensor
B2Temperature sensor
B3Temperature limiter/
Overheating guard
B4Room thermostat
BTBatteryVehicle battery
DSIlluminated toggleOperating indicator (in
item S1)
EGlow plug
F1Fuse 10 AATM mini flat fuse
F2Fuse 5 AATM mini flat fuse
F3Fuse 20 AATM mini flat fuse
H1“Heating” symbol in
the display
Operating indicator
(in item P2)
X7Plug connector, 2-pinTo item A2
X812-pin plug
connection
X912-pin plug
connection
X10Plug connector, 2-pinW-Bus Diagnostics
X11Plug connector, 2-pinTo Y1
X129-pin plug connectionPower/Control
X13Plug connector, 8-pinTo X9 of item P2
X14Plug connector, 1-pinTo pin-10 of item X9
X15Plug connector, 3-pinTo optional blower
X165-pin relay socketVehicle fan interface
Y1Metering pumpFuel pump for heater
To it e m A 2
To item P2
Harness
(see
)
interface systems
(Sleeper Pak™)
harness option
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Page 28
CIRCUIT DIAGRAMSTHERMO 90 ST
Yellow
Brown
Brown
Brown
Brown
Black
Blue
Black
Blue
White/Blue
Violet/Blue
Gray
Orange
Orange
Green
Blue
Brown
VioletViolet
Violet
Gray
Gray
Green
Green
Red
Yellow
E
M1
MM
M2
B3
B1B2
Y1
A1
F3
F2
F1
Red
White
Red
Red
Red
1
2
X10
Yellow/Red
A
B
CDE F
BDC
S1
DS
K1
86
85
87
30
Brown
Brown
Brown
RedRed
Red
BT
F5
Black
White
Red
A
EFGHJ
Brown
Gray
Red/Black
Black
Black
WhiteWhite
Violet
White
White
Violet
Brown
Black
Green
Red
Red
Red
Red
Brown
Brown
Brown
White
White
Brown
87a
1
5
2
4
3
ABC
X15
X12
X16
B4
Green
Green
White
White
Black
Violet
Black
Black
Optional Blower Interface Harness P/N 905613B
Black
Green
White
12568
10
11
A2
X8
4
3
7
9
12
12 1212222411112
X2X4X1X5X6X7X3
X11
12
12V +
GND
1
1
0
0
M2
A
B
X15
X12
1 2
X11
X10
X8
X4/X5/X6/X7
2
1
X3
2
C
1 2
1
2
1
3
5
7
9
11
1
Figure 13: Thermo 90 ST with On/Off switch - connection diagram (Includes optional blower interface harness)
Webasto Product N.A., Inc.22www.techwebasto.com
EB2B3
B1
M1
X2
X1
1
2
1
4
3
2
Page 29
THERMO 90 STCIRCUIT DIAGRAMS
2
8
11
101
12
7
4
H3
P2
H1
H6
6
3
4
1
2
7
5
8
X1
X8
X13
X11
X10
X12
X15
X9
X3
X4/X5/X6/X7
3
6
9
12
1 2
1 2
1
2
A
B
C
3
4
6
7
8
5
1
2
EB2B3
M1
M2
B1
1
3
5
7
9
11
3
4
1
2
1
2
1
2
1
2
X2
F3
F2
F1
Red
White
Red
Red
Red
X8
1
2
4
3
5
6
789
10
11
12
12 1212222411112
1
2
X10
Yellow/Red
Yellow
Brown
Brown
Brown
Brown
Black
Blue
Black
Blue
White/Blue
Violet/Blue
Gray
Orange
Orange
Green
Blue
Brown
VioletViolet
Violet
Gray
Gray
Green
Green
Red
Yellow
A
B
CDE F
BDC
Brown
Brown
Brown
RedRed
Red
BT
F5
A
EFGHJ
Brown
Gray
Red/Black
Black
Black
WhiteWhite
Violet
White
Violet
Brown
Black
Green
Red
Red
Red
Red
Brown
Brown
Brown
White
White
Brown
E
M1
MM
M2
B3
B1B2
Y1
A1
A2
ABC
Violet
Brown
Brown
Red
Yellow
Black
Gray
Black
Red
White
Violet
X13
X14
X9
12
X2X4X1X5X6X7X3
X11
X15
X12
Figure 14: Thermo 90 ST with 7-day digital timer model 1531 - connection diagram
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Page 30
CIRCUIT DIAGRAMSTHERMO 90 ST
This page for your notes.
Webasto Product N.A., Inc.24www.techwebasto.com
Page 31
THERMO 90 STSERVICING WORK
8.SERVICING WORK
8.1GENERAL
This section describes the servicing work that can be
carried out on the heater when it is installed.
8.2WORKONTHE 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 slowing down as a result of the risk
of the heater overheating and the overheating guard
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.
8.3WORKONTHE VEHICLE
CAUTION: A temperature of 90 °C (194 °F)
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.
8.4HEATER TRIAL
WARNING: The heater must not be
operated in enclosed areas such as garages
and workshops without an emissions
extraction system, even if the heater is
equipped with a timer.
8.5SERVICE WORK
NOTE: The heater should be operated for
approximately 20 minutes every 4 weeks to
prevent mechanical parts seizing.
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.
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Page 32
SERVICING WORKTHERMO 90 ST
15
14
13
11 Fuel standpipe
12 Heat exchanger - vehicle heating
13 Digital timer
14 Coolant hose to heater inlet
15 Return coolant hose from heater
11
12
6
7
1
10
9
2
8
3
5
4
6 Fuse block
7 Vehicle batteries
8 Fuel line
9 Fuel metering pump
1 Thermo 90 ST water heater
2 Control unit
3 Circulating pump
4 Combustion air intake
10 Fuel filter (optional)
5 Exhaust outlet with muffler
Figure 15: Installation example of a heater in a truck
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Page 33
THERMO 90 STSERVICING WORK
iØ2mm
iØ2mm
iØ2mm
iØ2mm
I
2
I
2
I
1
I
1
max. 3m (9.8 ft.)
H
S
I
2
I
1
+
≤ 10 m (32.8 ft.)
≤ 1.2 m (3.9 ft.)
≤ 8.8 m (28.8 ft.)
I
1
I
2
8.6VISUAL INSPECTIONSAND INSTALLATION
I
NSTRUCTIONS
8.6.1CONNECTIONTOTHE VEHICLE COOLING
YSTEM
S
In thermostat circuits, only use thermostats which start to
open at < 65 °C (< 149 °F).
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. 15. The system must contain at least
6 liters (6.34 quarts) 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 proper bleeding)
Permissible fuel inflow
height H (m)
At max. pressure (bar) in
fuel line
0.00 m (0.00 in.)0.20 bar (2.9 PSI)
1.00 m (39.4 in.)0.11 bar (1.6 PSI)
2.00 m (78.7 in.)0.03 bar (0.44 PSI)
Maximum fuel intake
height S (m)
At max. negative
pressure (bar) in fuel tank
0.00 m (0.00 in.)-0.10 bar (-1.45 PSI)
0.50 m (19.7 in.)-0.06 bar (-0.87 PSI)
1.00 m (39.4 in.)-0.02 bar (-0.29 PSI)
NOTE: A sign must be affixed to the fuel filler
neck warning that the heater must be switched
off before refuelling.
NOTE: The hose clips must be tightened with
a torque of 4 Nm.
The cooling system must be bled carefully before using
the heater for the first time or after replacing the
coolant. The heater and lines should be installed in such
a way as to ensure static bleeding.
Proper bleeding can be identified by the circulating pump
operating almost silently. Poor bleeding may cause the
resetting temperature limiter to trip while the heater is in
operation.
8.6.2CONNECTIONTOTHE 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.
Figure 16: Fuel supply
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Page 34
SERVICING WORKTHERMO 90 ST
> 25 mm (> 1 in.)
25 mm (1 in.)
Plastic tank
Sealing ring
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. 17, 18 and 19).
Hole pattern
Max. depth
Sealing ring
Metal tank fitting
or sender plate
Figure 19: Fuel standpipe for a plastic or metal tank
(extraction through metal tank fitting)
Figure 17: Webasto fuel standpipe
Figure 18: Fuel extractor from a plastic or metal tank
NOTE: Only use this style of standpipe with
metal fuel tanks.
(extraction through tank drain screw)
NOTE: Deburr the cut on the fuel extractor
after sawing it off and remove any metal chips
Vehicles with Gasoline Engines
The heater must be integrated into the return line of fuel
systems in carburetor and injection engines with a return
line.
In carburetor 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.
IMPORTANT!
•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 tee
(Fig. 20).
The fuel extractor must be fitted in such a way that any
air or gas bubbles are automatically discharged towards
the tank (Fig. 20). Air or gas bubbles may be produced in
the vehicle’s fuel line if there are leaks in the carburetor
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Page 35
THERMO 90 STSERVICING WORK
a= 6Ø
8Ø
10Ø
12Ø
0-60°
Ø5
0-60°0-60°
0-60°0-60°
0-60°
From Tank
To Engine
To Fuel Metering Pump
Clamp
Bubble
Bubble
Wrong
Correct
0°
0-90°0-90°
Install in horizontal position only!
12 V and 24 V – Diesel DP 30 (with damper)
or vehicle fuel pump or if the ambient temperature is
higher than the evaporation temperature of the fuel.
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.
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 debris and high
temperatures (exhaust line).
The fuel lines must be secure at the connections using
hose clips to prevent their slipping.
Connecting Two Fuel Lines with a Hose
The correct procedure for connecting fuel lines with
hosing is shown in Fig. 21.
Figure 20: Webasto fuel extractor tee installation
8.6.2.2 FUEL LINES
Only steel, copper and plastic lines of plasticized, light
and temperature-stabilized PA11 or PA12 (for example
Mecanyl RWTL) according 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 sidecutting pliers.
Since the lines cannot normally 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 (5/32 in) and these will cause malfunctions if
the lines sag or are routed downwards. The diameters
specified in Fig. 16 will ensure that bubbles do not form.
The lines should not be routed downwards from the
metering pump to the heater.
www.webasto.us29Webasto Product N.A., Inc.
Figure 21: Fuel line connections
8.6.3FUEL METERING PUMP
The metering pump is a combined delivery, metering and
shut-off system and is subject to certain installation
criteria (Fig. 16 and 22).
Figure 22: Metering pump, installation position and
attachment
8.6.3.1 INSTALLATION POSITION
Before installing the fuel metering pump, ensure that the
maximum pressure occurring at the fuel pickup point is
less than 0.2 bar (2.9 PSI).
Page 36
SERVICING WORKTHERMO 90 ST
A
Ø 5
0° - 90°
10°
It is advisable to install the metering pump in a cool
place. The maximum ambient temperature must not
exceed +20 °C (+68 °F) for gasoline and
+40 °C (+104 °F) 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 INSTALLATIONAND ATTACHMENT
The metering pump must be secured with a vibrationdamping mounting. Its installation position is limited as
shown in Fig. 22 in order to ensure effective automatic
bleeding.
As a result of the risk of corrosion, only genuine Webasto
parts may be used for the plug connections between the
metering pump and the metering pump wiring harness.
8.6.4FUEL FILTER
Only a Webasto filter, P/N 50487171A, is allowed to be
used if the fuel is expected to be contaminated. Install
vertically if possible, however at most horizontally (check
flow direction).
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
(5/32 in) 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.
2
A ventilation opening measuring at least 6 cm
(1 in2) 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).
8.6.6EXHAUST 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.
Figure 23: Fuel filter
8.6.5COMBUSTION 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.
An attachment is required no further than 150 mm (6 in)
from the end of the exhaust pipe to ensure that the
angle of 90° ±10° is achieved.
Discharge direction
more or less vertical
90° ± 10°
Figure 24: Exhaust pipe opening, installation position
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Page 37
THERMO 90 STSERVICING WORK
The opening of the exhaust pipe must not point towards
the front of the vehicle (see Figure 24).
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 your local jurisdiction for statutory
regulations for other requirements that may be in force.
8.7REMOVALAND 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
2. Connect the coolant hoses and secure with hose
clips. Tighten the hose clips to 5 Nm (44 lb-in).
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.
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.
8.7.2CHANGINGTHE 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 9.2.1.
8.7.3CHANGINGTHE 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 9.2.2.
8.7.1HEATER, REMOVALAND INSTALLATION
8.7.1.1 REMOVAL
1. Disconnect the battery.
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.
8.7.4CHANGINGTHE 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 9.2.3.
8.7.5CHANGINGTHE 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 9.2.4.
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).
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Page 38
SERVICING WORKTHERMO 90 ST
This page for your notes.
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Page 39
THERMO 90 STREPAIR
9.REPAIR
9.1GENERAL
This section describes the repair work that may be carried
out on the Thermo 90 ST heater after it has been
removed from the vehicle. Any further dismantling will
invalidate the warranty. Only use the spare parts from
the appropriate spare parts kits for assembling the
heater.
9.1.1WORKON STRIPPED-DOWN COMPONENTS
CAUTION: All sealing elements between
the stripped-down components must
always be discarded and replaced with
new.
9.1.1.1 CLEANING
•Clean all stripped-down components.
•Remove all seal residue on the components carefully
using a suitable tool.
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.
9.2DISMANTLINGAND ASSEMBLING
9.2.1REPLACINGTHE CIRCULATING PUMP
9.2.1.1 REMOVAL
1. Remove the heater (see 8.7.1.1).
2. Remove the screws (4, Fig. 25).
3. Remove the clip (3) and circulating pump (2).
4. Unplug electrical cable from control unit.
5. Complete the work on stripped-down components
(see 9.1.1).
9.2.1.2 INSTALLATION
1. Apply acid-free grease (Vaseline) to the sealing ring
(1, Fig. 25).
2. Place the circulating pump (2, Fig. 25) in the
assembly position and attach with the clip (3) and
screws (4).
3. Tighten the screws (4) to 3 Nm (26.5 lb-in) ±10%.
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. Remove the clip (2, Fig. 26) and pull off the
protective cap (1).
3. Use a screwdriver to lever off the retaining spring
and remove the temperature limiter (3).
4. Unplug electrical cable from control unit.
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!
9.2.2.2 INSTALLATION
CAUTION: Incorrect installation will cause
the heat exchanger to melt.
9.2.3REPLACINGTHE TEMPERATURE SENSOR
9.2.3.1 REMOVAL
1. Remove the heater (see 8.7.1.1).
WARNING: Leaking hot coolant can cause
burns.
2. Unscrew and remove the temperature sensor
(6, Fig. 26) and remove it together with the round
sealing ring (5).
3. Unplug electrical cable from control unit.
4. Complete the work on stripped-down components
(see 9.1.1).
9.2.3.2 INSTALLATION
1. Apply acid-free grease (Vaseline) to the round
sealing ring (5, Fig. 26).
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 (13.3 lb-in) ±10%.
3. Plug electrical cable into control unit.
4. Install the heater (see 8.7.1.2).
1. Insert the new temperature limiter (3, Fig. 26) 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 (8.8 lb-in) ±10%.
4. Plug electrical cable into control unit.
5. Install the heater (see 8.7.1.2).
www.webasto.us35Webasto Product N.A., Inc.
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REPAIRTHERMO 90 ST
1
2
3
4
6
5
1 Protective cap
2 Clamp
3 Temperature limiter
4 Heat exchanger
5 Round sealing ring
6 Temperature sensor
Figure 26: Replacing the temperature limiter and
temperature sensor
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Page 43
THERMO 90 STREPAIR
9.2.4REPLACINGTHE COMBUSTION AIR FAN
9.2.4.1 REMOVAL
1. Remove the heater (see 8.7.1.1).
2. Remove the screws (2, Fig. 27).
3. 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 ST heater with flangemounted control unit.
4. Unplug electrical cable from control unit.
5. Complete the work on stripped-down components
(see 9.1.1).
1 Combustion air fan
2 Screw (2)
3 Shaped sealing ring
4 Burner head
5 Control unit
2
3
9.2.4.2 INSTALLATION
NOTE: Insert the shaped seal (3, Fig. 27)
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 (26.5 lb-in) ±10%.
NOTE: Install the control unit if necessary on
the Thermo 90 ST heater with flange-mounted
control unit.
3. Plug electrical cable into control unit.
4. Install the heater (see 8.7.1.2).
5
Figure 27: Replacing the combustion air fan
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1
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REPAIRTHERMO 90 ST
Glow pin
Flame monitor
9.2.5REPLACINGTHE BURNER, FLAME MONITORAND
LOW PIN
G
9.2.5.1 REMOVAL
1. Remove the heater (see 8.7.1.1).
2. Remove the combustion air fan (see 9.2.4.1).
3. Remove the screw (5, Fig. 28) 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 air swirl plate (2).
7. Pull the flame monitor (7) and glow pin (6) from the
burner (1) and remove.
8. Perform a visual check for assessing the burner
(see 5.4).
9. Complete the work on stripped-down components
(see 9.1.1).
9.2.5.2 INSTALLATION
1. Place the air swirl plate (2, Fig. 28) onto the burner
(1).
2. Carefully insert the flame monitor (7) and glow pin
(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 pin (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 pin as shown in the figure!
Webasto Product N.A., Inc.38www.techwebasto.com
5. Secure the bar (8) using the nuts (10). Tighten the
nuts to 3 Nm (26.5 lb-in) ±10%.
6. Secure the fuel line using the screw (5) and
washer (4). Tighten the screw to 3 Nm (26.5 lb-in)
±10%.
7. Install the combustion air fan (see 9.2.4.2).
8. Plug in any electrical cables removed from the
control unit.
Figure 28: Replacing the burner, flame monitor and
glow pin
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REPAIRTHERMO 90 ST
9.2.6REPLACINGTHE BURNER HEAD
9.2.6.1 REMOVAL
1. Remove the heater (see 8.7.1.1).
2. Remove the combustion air fan (see 9.2.4.1).
3. Remove the burner, flame monitor and glow pin
(see 9.2.5.1).
4. Remove the mounting screw of the V-clamping
collar (2, Fig. 29 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).
9.2.6.2 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. 29) 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 (26.5 lb-in) ±10%.
3. Install the burner, flame monitor and glow pin
(see 9.2.5.2).
4. Fit the combustion air fan (see 9.2.4.2).
5. Install the heater (see 8.7.1.2).
1 Burner head
2 V-clamping collar
3 Heat exchanger
3
2
1
Figure 29: Replacing the burner head
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THERMO 90 STREPAIR
9.2.7REPLACINGTHE HEAT EXCHANGER
9.2.7.1 REMOVAL
1. Remove the heater (see 8.7.1.1).
2. Remove the circulating pump (see 9.2.1.1).
3. Remove the temperature limiter (see 9.2.2.1).
4. Remove the temperature sensor (see 9.2.3.1).
5. Remove the combustion air fan (see 9.2.4.1).
6. Remove the burner, flame monitor and glow pin
(see 9.2.5.1).
7. Remove the burner head (see 9.2.6.1).
8. Complete the work on stripped-down components
(see 9.1.1).
9.2.7.2 INSTALLATION
1. Install the burner head (see 9.2.6.2).
2. Install the burner, flame monitor and glow pin
(see 9.2.5.2).
3. Fit the combustion air fan (see 9.2.4.2).
4. Install the temperature sensor (see 9.2.3.2).
5. Install the temperature limiter (see 9.2.2.2).
6. Install the circulating pump (see 9.2.1.2).
7. Install the heater (see 8.7.1.2).
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REPAIRTHERMO 90 ST
This page for your notes.
Webasto Product N.A., Inc.42www.techwebasto.com
Page 49
THERMO 90 STPRODUCT INFORMATION
10. PRODUCT INFORMATION
No new or updated information available at this time.
www.webasto.us43Webasto Product N.A., Inc.
Page 50
PRODUCT INFORMATIONTHERMO 90 ST
This page for your notes.
Webasto Product N.A., Inc.44www.techwebasto.com
Page 51
THERMO 90 STWARRANTY
W
ARRANTYCOVERAGE ANDLIMITATIONS
Webasto Product North America, Inc. (herein after referred to Webasto) warrants their heaters
and heater kits against defects in material and workmanship for two (2) years effective at the time
of installationor vehicle registration date for Original Equipment installations (OE). This warranty
period may not exceed three (3) years from the original date of sale by Webasto. This warranty
period may be superseded by a contractual agreement.*
*Warranty coverage for Marine and Off-road applications containing DBW series heaters and the
CSL Cargo Heaters are limited to a maximum of 3,000 hours of usage. All other models are
limited to 2,000 maximum hours.
Replacement parts are covered for six (6) months or the remainder of the original warranty period,
which ever is longer. Replacement heaters are considered a “Replacement Part.”
The intent of the Webasto warranty is to protect the end-user heater from such defects and provide
free repair and replacement of defective parts in the manner provided herein. During the warranty
period the exclusive remedy will be for Webasto, at their discretion, to repair or replace those parts
which are demonstrated to be defective in material or workmanship.
While warranty is provided to the "end-user", it is to be administered and serviced through an
authorized Webasto dealer in accordance with the Webasto warranty policy or contractual
agreement between Webasto and a second party.
Limitations: Webasto specifically excludes and limits from warranty the following:
· Normal wear of service parts: (fuel nozzles, filters and overheat fuses are not covered).
· Removal and replacement of heater (with the exception of the Thermo Top C).
· Damage to product in transit. All claims must be filed with carrier.
· Improper installation, which is not in accordance with valid, supplied installation instructions or
approved OEM applications.
· Deterioration due to normal wear, corrosion, abuse, damage, accident, improper storage or
operation.
· Modification of product by alteration, use of non-genuine parts or repair by unauthorized
personnel.
· Economic loss for expenses related to travel, vehicle disability, personal injury or other
incidental or consequential damages arising from any breach of this expressed warranty.
Owner's Responsibilities:
1) Service heater at the start of each season by an authorized Webasto dealer (Service parts
including; fuel nozzles, filters and overheat fuses are not covered under warranty).
2) A Warranty Registration Card is included with the sale of each heater. It is the owner's
responsibility to complete this card and return it to Webasto for registration. A proof of
purchase is required for all heaters that are not registered.
This warranty gives you specific legal rights and you may also have other rights which vary by State or Province
THE WARRANTY DESCRIBED IN THIS POLICY SHALL BE IN LIEU OF ANY OTHER WARRANTY,
EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO, ANY IMPLIED WARRANTY OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.