0400 - Function description: B. Operating principle with function diagram Auxiliary heater Models 124, 126, 201

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

approx. 120 s.

hour has elapsed.

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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-

running

running 60 s

max. 80 s

Preglow 30 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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aktualizacji.

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