Webasto Air Top 2000 S B, Service And Repair Manual

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3. Functional Description
3.1 Functional Description Air Top 2000 S
301
Air Top 2000 S
3 Functional Description
3.1.1 Control Element
The control element is used to switch the air heater on
and off, set the desired room temperature (air intake tem-
perature between 10 °C and 45 °C), and to unlock a
failure interrupt condition.
The green LED indication is used to indicate the opera-
ting condition (LED permanently on) and an overheat
condition (LED flashes).
3.1.2 Switch-On
The control element is set to the desired room tempera-
ture. When switching the air heater on, the operating indi-
cator is illuminated and the glow plug is activated
(cycled). The motor of the combustion and heating air
fan starts high-speed operation for 1 second (break-
away moment) and is then under slow-down control to
approx. 30% (Diesel) or 50% (fuel) of full speed.
NOTE
Should the temperature of the intake air be above the se-
lected, rated temperature, only the motor of the combus-
tion and heating air fan will operate (control idle). Start
operation will be initiated with a heating air temperature
below the rated temperature.
The flame sensor function is checked. If the flame sen-
sor at this time already signals “flame”, there will be a
120 second run-down and an error lockout of the control
unit. A malfunction of any other component monitored
causes an error lockout without run-down.
After approx. 20 seconds (for fuel operated heaters after
approx. 15 seconds) the fuel dosing pump is activated.
After another 25 seconds the speed of the combustion
and heating air fan is continuously increased to a higher
rate and combustion begins. As soon as a flame is
detected, combustion will be stabilized (see 3.1.3).
Should no normal combustion be achieved within 120
seconds (for fuel operated heaters after approx. 115
seconds), the speed of the combustion and heating air
fan is increased for approx. 30 sec and there will be an
automatic repeat start with the glow plug activated and
fuel dosing pump deactivated (no fuel supply).
Should no proper combustion develop within 120 sec-
onds (for fuel-operated within 115 seconds) the combus-
tion and heating air fan speed is increased to full load for
approx. 30 seconds (15 seconds for fuel-operated
heaters) with the glow plug on and the dosing pump off
(no fuel delivery) with a subsequent automatic restart.
Should the no-combustion-condition persist, after an-
other 80 seconds (for fuel operated heaters after approx.
85 seconds) there will be a switch-off by error lockout
(see 3.1.8) with a run-down of the combustion and heat-
ing air fan lasting 120 seconds at 2/3 of its max. speed.
2. Start (automatic restart)
Fan speed is again reduced to approx. 30% (for fuel
operated heaters to approx. 50%) and fuel is delivered.
During the next 20 seconds fan speed is increased to ap-
prox. 60% (for fuel-operated heaters to approx. 75%) of
full speed. As soon as a flame is detected within the next
55 seconds, combustion will be stabilized. Should there
be no flame condition after a total fuel delivery period of
180 seconds, fuel delivery will be stopped and the glow
plug deactivated. The combustion air fan continues full
load operation for another 120 seconds (run-down) and
the heater enters the error lockout condition.
3.1.3 Stabilization
Diesel Operated Heaters
With the glow plug activated the operating speed of the
combustion and heating air fan is increased. After an-
other 20 seconds the speed of the combustion and heat-
ing air fan is continuously increased within 17 seconds
to full load for full heat.
NOTE
This operating condition is omitted if the set temperature
(control idle) has already been achieved once.
The glow plug is deactivated and heating operation com-
mences. A flame-out during speed up control causes a
restart, 5 restarts an error lockout of the heater.
Fuel Operated Heaters
With the glow plug activated the operating speed of the
combustion and heating air fan is continuously increased
within 4 seconds to full load for full heat. This operating
condition will be omitted if the start occurs after a control
idle period.
The glow plug is deactivated and heating operation com-
mences. A flame-out during speed up control causes a
restart, 5 restarts an error lockout of the heater.