Combustion Air Fan; Heat Exchanger; Temperature Sensor; Temperature Limiter - Webasto Thermo 90 ST D Service And Repair Manual

GENERAL DESCRIPTION
2.1 C A
OMBUSTION IR
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

2.2 H E
EAT XCHANGER
In the heat exchanger, the heat generated by
combustion is transferred to the coolant circuit.

Temperature Limiter

Temperature Sensor

Figure 3:

Heat exchanger

Webasto Product N.A., Inc.
F
AN
2.3 T
EMPERATURE
The temperature sensor records the coolant temperature
at the coolant outlet of the heater as an electrical
resistance. This signal is fed to the control unit where it
is processed.
2.4 T
EMPERATURE
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.
2.5 B I
URNER NSERT
The fuel is distributed over the burner cross-section in the
combustion pipe in the burner insert.
2.6 G P
LOW IN
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.

Glow Pin

Figure 4: Burner Assembly
2.7 F M
LAME ONITOR
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.
4
THERMO 90 ST
S
ENSOR
L
IMITER
Burner Insert

Flame Monitor

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