Webasto Air Top 3500 ST Workshop Manual - page 16
Air Top 3500/5000
3 Functional Description
303
3.3
Heating Operation
During operation there is a flow of combustion gasses
through the heat exchanger. The heat of combustion is
thereby dissipated onto the heat exchanger walls and is
absorbed by the heating air delivered from the heating air
fan to be routed to the vehicle passenger cabin.
The temperature of the heating air taken in is measured
by a temperature sensor located at the suction side of the
heater or with an external temperature sensor. If the
measured temperature is below that set with the control
element, the performance of the heater will increase up to
maximum.
To increase the heater life in continuous operation the
dosing pump rate of delivery is reduced for 15 seconds
every 10 minutes. After reaching the temperature set with
the control element heater performance is reduced by
lowering the combustion and heating air fan speed and by
decreasing the dosing pump rate of delivery.
3.4
Control Idle
NOTE
The combustion and heating air fan of heaters installed in
boats or ships will not operate during control idle.
When exceeding the air intake temperature set with the
control element at minimum heating performance, the
dosing pump is deactivated and combustion terminates.
During run-down lasting 90 seconds and during the total
of the control idle period the combustion and heating air
fan operates at minimum speed.
If the temperature sensor senses a temperature below the
one set with the control element, the heater will restart
(without break away torque).
NOTE
New control element settings will be executed by the
control unit/heater with a time delay.
3.5
Switch off
Switching the heater off extinguishes the operating
indicator light of the control element.
Should fuel delivery have commenced, it will be shut off
immediately upon switch off. The heater will be cooled
down by a run-down of 180 seconds at full speed.
NOTE
Reactivation of the heater during run-down is permitted.
The run-down will first be completed with a subsequent
restart.
3.6
Heater Functions when installed in
ADR Vehicles
Switch off of the heater with the control element has no
influence on the run-down.
A short run-down (max. 20 seconds) will be automatically
initiated in case the:
•
vehicle engine is stopped
•
a conveyor device is activated
The short run-down period depends on the operating
condition.
The short run-down period is always 20 seconds.
Run-down speed is the same speed as before switch off.
After an ADR switch off the control unit is in "error lockout"
position. Prior to reactivation the control element must be
set to "OFF".