Webasto Air Top Evo 3900 Workshop Manual page 13

Air Top Evo 3900/5500
2.4 Control unit
The control unit is the central component for ensuring the
function is maintained and for monitoring the heater's
operation. A temperature sensor in the control unit is
designed to control the room temperature. An external
temperature may also be connected to all the heaters.
If a fault occurs, an error code will be output in the display
of the combination timer. If the heater has a control
element, the ON control light will flash. In addition the
heater can be checked using a personal computer (see
PC heater diagnostic operating manual).
Control module
2.5 Glow plug / Flame monitor
The glow plug also acts as a flame monitor.
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 on the
side facing the flame.
As a flame sensor the glow plug reacts in the same way
as 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 sensor
whenever the heater is operating.
Glow plug / Flame monitor
2.6 Overheating sensor
The overheating sensor measures the temperatures in
the rib area of the heat exchanger whenever the heater is
operating.
The control unit evaluates the signal and protects the
heater from hot air outlet temperatures above 150 °C and
surface temperatures above 80 °C by shutting down the
combustion process and blowing cold air over the heater.
The heater then suffers a fault lock-out and can by
restarted by being switched off and on again (see 3.2).
Overheating sensor
2.7 Metering pump
The metering pump is a combined transport, metering and
shut-off system for supplying fuel from the vehicle's tank
to the heater.
Metering pump DP 30.2/3
2 General description
203