83-400 Function description
B. Operating principle with function diagram
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Note If proper combustion is still not achieved
As of approx. 08/86 the control unit (N33) within 120 s during the repeat start, the
control unit (N33) switches off the auxiliary
Webasto no. 439.789 was replaced by the
heater without any after-running and moves
control unit (N33) with Webasto no. 105.499.
into the fault mode. After the cause of the
fault has been eliminated, the automatic
Temperature-switching points and the after-
cutout is deactivated by switching the
running of the new control unit (N33) have
auxiliary heater off and on again.
been modified (refer to function diagrams). Once the coolant in the heater has reached a
To enable the car heater heated by the temperature of approx. 55°C, the heater
auxiliary heater to supply warm air to the blower switches on automatically.
interior, blower switch and heater switch If the coolant temperature in the heater
must be moved into the following positions: reaches approx. 80°C, heating output is
On models 124, 126 with automatic heater reduced to approx. half. If this causes the
control and on model 201, blower switch to coolant temperature to drop to approx. 70°C,
position 1 so that the main air vent opens. the system switches back again to full
On models 124 and 126, the temperature heating capacity. If, however, a coolant
selector(s) do not need to be turned (normal temperature of approx. 85°C is reached in
position approx. 22°C). the heater at half heating capacity, the
On model 201 heater switch to max. heat control unit (N33) switches off the fuel
so that the blending flaps direct the cold air metering pump and 60 s later (after-running)
drawn in over the heat exchanger. also the combustion air blower. This after-
Operating principle with control unit running is performed at an increased speed.
(N33) Webasto no. 439.789 The circulating pump and heater blower
If the auxiliary heater is switched on with the remain running.
timer, the green operating indicator lamp Once the coolant temperature has dropped
comes on and at the same time the to approx. 80°C, the glow plug, fuel metering
circulating pump and glow plugs are pump and combustion air blower again
switched on. Approx. 30 s after switching on operate as during the switch-on phase. The
the heater, the fuel metering pump begins to start phase is performed at full heating
deliver fuel. After a further approx. 5 s, the capacity; after the flame monitor has taken
combustion air blower starts and combustion over the control, the heater is reduced back
commences. A flame monitor monitors to half heating capacity. This alternating
combustion and switches off the glow plug cycle of switching combustion on and off is
after combustion has stabilized. If perfect repeated until the system cuts out
combustion is not achieved, the starting automatically after max. 1 hour or is
operation is automatically repeated after switched off manually with the timer before 1
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approx. 120 s. hour has elapsed.
Function diagram, control unit (N33) up to approx. 07/86 (Webasto no. 439.789)
Switch on
Start of combustion
Full-load operation below 80°C
above 55°C
Part-load operation above approx. 80°C
Start of combustion interval above
approx. 85°C
End of combustion
interval at approx.
80°C
Glow plug
Circulating pump
Fuel metering
pump
Combustion air
blower
Flame monitor
Heater blower
Fuel feed 5 s
After-running 60 s
Preglow 30 s
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End of combustion interval at 80°C
Start of combustion
Full-load operation below 80°C
Part-load operation above approx.
80°C
Full-load operation when dropping to
70°C
Switch-off
End of
operation
Glow plug
Circulating pump
Fuel metering
pump
Combustion air
blower
Flame monitor
Heater blower
Fuel feed 5 s
After-running
60 s
Preglow 30 s
Function diagram, control unit (N33) as of approx. 08/86 (Webasto no. 105.499)
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Switch on
Start of combustion
Full-load operation below
78°C
above 55°C
Part-load operation above approx.
78°C
Start of combustion interval above
approx. 86°C
End of combustion
interval at approx.
78°C
Glow plug
Circulating pump
Fuel metering
pump
Combustion air
blower
Flame monitor
Heater blower
Optically Electronically
Fuel feed 5 s
controlled after- controlled after-
running running 60 s
Preglow 30 s max. 80 s
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End of combustion interval at 78°C
Start of combustion
Full-load operation below
78°C
Part-load operation above approx.
78°C
Full-load operation when dropping to
70°C
Switch-off
End of
operation
Glow plug
Circulating pump
Fuel metering
pump
Combustion air
blower
Flame monitor
Heater blower
Optically controlled
Fuel feed 5 s
after running max. 80 s
Electronically controlled
Preglow 30 s
after running 60 s
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