3.
Functional Description
3.1
Functional Description Air Top 2000
without Diagnosis (Fig. 301)
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).
NOTE
After application of power upon switch-on of the battery
switch and selecting the control element “ON”, the con-
trol unit enters the “error lockout” condition. Prior to a re-
activation the control element has to be placed to “OFF”.
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.
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.
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 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 3.1.9) with a run-down of the combustion and heat-
ing air fan lasting 120 seconds at 2/3 of its max. speed.
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.
A flame-out during the speed rise control period causes
a repeat start.
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. A flame-out dur-
ing the speed rise control period causes a repeat start.
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
vehicle 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 in case of 12 Volt
heaters also by means of an externally located tempera-
ture sensor. A temperature below the one set with the
control element increases the heater performance up to
maximum heat.
In order to extend the burner idle period of Diesel oper-
ated heaters during permanent operation with a heating
performance in excess of 1.2 kW, the fuel dosing pump
delivery rate is reduced every 30 minutes for 20 seconds.
A heating performance less than 1.2 kW causes the fuel
delivery to the dosing pump to be interrupted every 30
minutes for 4 seconds. For both types of heaters (fuel
and Diesel) heating operation is shortly interrupted every
9 hours like in 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 pump is reduced.
When exceeding the air intake temperature set with the
control element during minimum heating performance,
the dosing pump is deactivated after 5 seconds and com-
bustion terminates.
NOTE
The control unit/air heater reacts to new settings of the
control element with a time delay.
301
Air Top 2000
3 Functional Description