Webasto Air Top 2000 S B, Service And Repair Manual

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3 Functional Description
Air Top 2000 S
3.1.4 Heating Operation
During operation the combustion exhaust gasses flow
through the heat exchanger charging its walls with com-
bustion heat, which in turn is taken up by the heating air
delivered by the heating air fan to be routed to the ve-
hicle interior.
The temperature of the heating air sucked in is
measured by means of a temperature sensor fitted to
the air intake side of the air heater or by means of an ex-
ternally located temperature sensor.
A temperature below the one set with the control ele-
ment increases the heater performance up to maximum
heat. In order to extend the burner idle period of Diesel
operated heaters during permanent operation with a
heating performance in excess of 1.1 kW, the fuel dos-
ing pump delivery rate is reduced every 15 minutes for
20 seconds.
A heating performance less than 1.1 kW causes the fuel
delivery to the dosing pump to be interrupted every 30
minutes for 4 seconds. Additionaly heating operation is
briefly suspended every 9 hours like in control idle. For
Diesel-operated heaters this is only applicable, if at this
time heating performance is less than 1.1 kW.
3.1.5 Control Operation
During control operation fan speed and dosing pump
rate of delivery are subject to heating performance.
The glow plug is deactivated.
3.1.6 Control Idle
After reaching the temperature set with the control ele-
ment, heating performance is controlled to decrease.
The speed of the combustion and heating air fan slows
down and the fuel delivery rate to the dosing pump is re-
duced. When exceeding the air intake temperature set
with the control element during minimum heating perfor-
mance, the dosing pump is deactivated after 5 seconds
and combustion terminates.
Fan speed remains constant for 35 seconds and is then
increased to approx. 60% of full speed for cooling the
heater down. the fan then continues to operate at ap-
prox. 30% of full speed until temperature is below the
temperature set with the control element. If temperature
falls below the one set with the control element, the
heater will restart (without break away).
NOTE
New settings on the control element are executed by the
control unit/heater with a time delay.
3.1.7 Switch-Off
Switching the heater off extinguishes the operation indi-
cation of the control element.
If no fuel has been delivered or if the air heater is in con-
trol idle, the air heater is deactivated immediately
without run-down.
If fuel supply has commenced it will be immediately
stopped at switch-off. Fan speed remains constant and
then decreases within 30 seconds to approx. 60% of full
speed. After this or with the flame sensor detecting “no
flame”, fan speed rises to maximum speed for 60 sec-
onds and run down for 120 seconds is initiated. Run-
down is at approx. 60% of full speed and is deactivated
automatically.
NOTE
Re-activation of the heater during run-down is permitted.
Run-down will be completed first with a subsequent re-
start.
3.1.8 Switch-off upon Failure
The control unit recognizes failures of individual air
heater components and malfunctions in the start se-
quence and in normal operation.
The air heater is deactivated and enters the error lock
out mode under the following conditions:
flame sensor open or short circuit
temperature sensor open or short circuit
glow plug open or short circuit
fan motor open or short circuit or fan speed wrong
dosing pump open or short circuit
overheating
low voltage below 10 Volt or high voltage above
15 Volt in excess of 20 seconds for 12 Volt heaters
low voltage below 20 Volt or high voltage above
30 Volt in excess of 20 seconds for 24 Volt heaters
A switch-off like in “switch-off” will be performed.
In case of overheating there will be no fuel supply. After
run-down the control unit is in the error lockout mode.
The operation indication outputs a flash code.
For error unlock the air heater has to be switched off
momentarily (at least 2 seconds) before switching on.