Combustion Tube; Circulation Pump; Control Unit; Flame Sensor - Webasto Thermo 90 Workshop Manual

Thermo 90
2.3 Temperature Sensor
The temperature sensor senses the coolant temperature
in the heat exchanger of the heater unit as electrical
resistance. This signal is fed to the control unit for
processing.
2.4 Temperature Limiter
The overheat protection (bimetal) protects the heater unit
from excessive operating temperatures. The overheat
protection responds at a coolant temperature higher than
105° C to switch off the heater.
2.5 Burner Insert
Within the burner insert fuel is distributed in the
combustion tube across the burner cross-section.
2.6 Glow Plug
The glow plug ignites the fuel/air mixture at the start of
heater operation. The glow plug is acting as an electrical
resistor and is located in the burner insert opposite to the
flame source.
Glow Plug
2.7

Flame Sensor

The flame sensor is a low-Ohm PTC resistor, changing
its resistance dependent on its heating by the flame.
The signals are routed to the control unit for processing.
The flame sensor monitors the flame operating condition
over the complete duration of heater operation.
Burner Insert
Flame Sensor
2 General Description
2.8

Combustion Tube

Inside the combustion tube the combustion of the fuel/air
mixture takes place, heating up the heat exchanger.
2.9

Circulation Pump

The circulation pump provides for circulation of the
coolant in the vehicle and heater circuits. The control unit
switches the pump on for operation throughout the entire
time of heater operation (also in control idle).
Circulation Pump

2.10 Control Unit

The control unit is the central controlling device for
functional sequencing and monitoring of the combustion
operation. It is located externally in the vehicle, but may
also be flanged to the combustion air fan on Thermo 90 S
heaters.
2.11 Dosing Pump
Fuel supply to the heater and its dosing is ensured
externally by a dosing pump. When the heater is
deactivated, it also serves as a shut-off facility.
The magnetic coil of the dosing pump receives the pulses
from the microprocessor of the control unit.
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