Webasto Air Top 2000 ST B Workshop Manual - page 15
Air Top 2000 ST
Description of operation
301
3
Description of operation
3.1
Control element
The control element is designed to switch the heater on and
off, adjust the required room temperature (intake
temperature between approx. 5 °C and 35 °C) and to reset
the heater after a fault.
The green LED serves as the On indicator (LED permanently
lit up) and as a fault signal (LED flashes).
NOTE
ADR operation:
After an operating voltage has been applied by switching
the battery isolation switch and control element to “ON”,
the control unit will be set to the “Fault lock-out” position.
Before it can be restarted, the control element must be set
to “OFF”.
3.2
Switching on
Set the control element to the required temperature.
If the hot air temperature is lower than the nominal
temperature the heater will start
NOTE
If the temperature of the hot air intake is above the set
nominal temperature, only the motor for the hot and
combustion air blower will start (control pause). Special
feature: The control pause speed is 0 rpm if boat heaters are
used.
The function of the flame monitor is checked. If the flame
monitor now reports “light”, the system will attempt to cool
the flame monitor for 60 seconds. If the flame monitor still
reports “light” the control unit will suffer a fault lock-out. If
another monitored component has suffered a fault, the
fault lock-out will take effect without any slow down time.
Start
When the heater is switched on the ON signal light will be
lit and the glow plug will be switched on (cycled). The motor
for the hot and combustion air blower will be set to approx.
50% of its maximum speed.
After approx. 40 seconds the fuel metering pump will start
and the flame formation will begin. To improve the starting
quality, the metering pump and combustion air blower are
started with different frequencies and speeds.
After a further 95 seconds (petrol) or 110 seconds (diesel)
the glow plug will be switched off and the existence of the
flame established.
Automatic restart
If no flame is detected, the starting procedure will be
repeated. The glow plug will be switched on again (cycled).
The motor for the hot and combustion air blower will be set
to approx. 25% of its maximum speed.
After approx. 30 seconds (petrol) or 50 seconds (diesel) the
fuel metering pump will start, and the flame formation will
begin. After a further 65 seconds (petrol) or 90 seconds
(diesel) the glow plug will be switched off and the existence
of the flame established.
If the heater has again failed to ignite properly, the it will be
shut down using a fault slow down procedure at maximum
speed after 180 seconds and will suffer a fault lock-out.
NOTE
After a restart the heater will suffer a fault lock-out. To reset
the fault switch the heater off briefly (at least 2 seconds) and
then on again.
3.3
Heating mode
Whilst the heater is operating the combustion gases pass
through the heat exchanger. During this process the
combustion heat is given off to the walls of the heat
exchanger, absorbed by the hot air transported by the hot
air fan and fed into the interior of the vehicle.
The temperature of the hot air intake is measured by a
temperature sensor on the intake side of the heater or an
external temperature sensor. If the measured temperature is
lower than the value set on the control element, the output
of the heater is increased to maximum heat output.
To increase the burner service life when it is used
continuously the transport capacity of the metering pump is
reduced for 10 seconds every 10 minutes.
In addition, heating mode is interrupted every 8 hours in the
same way as for a control pause.
3.4
Control mode
In the control mode the fan speed and the metering-pump
pumping quantity are dependent on the heating capacity.
The glow plug is off.
3.5
Control pause
After the temperature set on the control element has been
reached the heat output is reduced. The speed of the
heating and combustion air blower and the delivery rate of
the metering pump are reduced.