T
HERMO
90 / 90 S
2GENERAL DESCRIPTION
2-3
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 Pin
The glow pin ignites the fuel/air mixture at the start of
heater operation. The glow pin is acting as an electrical
resistor and is located in the burner insert opposite the
flame source.
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.
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).
2.10 Control Unit
The control unit is the central controlling device for
functional sequencing and monitoring of the combustion
operation. It is mounted to the heat exchanger on
Thermo 90 heaters and flanged to the combustion air fan
on Thermo 90 S heaters.
2.11 Fuel Dosing Pump
Fuel supply to the heater and its dosing is ensured
externally by a fuel dosing pump. When the heater is
deactivated, it also serves as a shut-off valve. The
magnetic coil of the dosing pump receives the pulses
from the microprocessor of the control unit.
