Webasto Air Top 2000 ST D Service And Repair Manual - page 12
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9
Webasto Product N.A., Inc.
AIR TOP 2000 ST
FUNCTIONAL DESCRIPTION
3.
FUNCTIONAL DESCRIPTION
3.1
C
ONTROL
E
LEMENT
(R
HEOSTAT
)
The control element is designed to switch the heater on
and off, adjust the required room temperature (intake
temperature between 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).
3.2
S
WITCH
O
N
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 sensor is checked. If
the flame sensor now reports “light”, the
system will attempt to cool the flame sensor for
60 seconds. If the flame sensor 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 (gasoline) or 110 seconds
(diesel) the glow pin 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
heater 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 (min. 2 seconds) and switch
back on.
3.3
H
EATING
M
ODE
While 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 blower 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
C
ONTROL
M
ODE
In control mode the blower speed and the metering
pump delivery rate are dependent on the heat output.
The glow pin is switched off.