0400 - Function description: electrical function of control unit Auxiliary heater Models 124, 126, 201 up to approx. 07/86

83-400

Function description

C. Electrical function, control unit up to approx. 07/86 (Webasto no.
439.789)

Note

A continuous voltage from terminal 30 is

The circulation pump (A6m1 or A31m1) of

supplied through the fuses of the auxiliary
fuse box (F12) to the following terminals of

the auxiliary heater operates even when the

the auxiliary heater:

ignition is switched on if, on model 201, the

Control unit (N33) terminals 1, 3 and 4 of

left-hand heater switch is turned to "heat", or

connector A and also at the timer (N34)

on models 124 and 126.02, if the car heater

terminal 2.

is in the heating mode (mono or duo valve

open).

Wiring diagram, auxiliary heater, model 201

Auxiliary heater unit

N34

Auxiliary heater timer

A6b1

Temperature sensor

R14

Blower motor preresistor group

A6f1

Temperature cutout

Air volume switch

A6m1

Circulating pump

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A6m1

Circulating pump

S46/1

Auxiliary heater microswitch

A6m2

Combustion air blower

Main ground (behind instrument cluster)

A6r1

Combustion air blower preresistor

W10

Battery ground

A6r2

Glow plug

X5/1

Interior terminal block

A6v1

Flame monitor, photoelectric cell

X76

Air volume switch/auxiliary heater

Electrical center

connection

F12

Auxiliary heater auxiliary fuse box

Y16

Auxiliary heater switchover valve

Blower motor

Y23

Auxiliary heater fuel metering pump

N33

Auxiliary heater control unit

To terminal block X6 terminal 58d

Blower control relay

To ignition starter switch terminal 15X

Circulating pump relay

To ignition starter switch terminal 30

Combustion air blower/full-load relay

To ignition starter switch terminal 15

Combustion air blower/part-load relay

* *

Ground cable only on cars with diesel

Glow plug relay

engine

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Starting by switching on with timer (N34)

Part-load switching (approx. half heating

and subsequent full-load operation (full

capacity)

heating capacity)

When a coolant temperature of approx. 80°C

If the contact in the timer (N34) is closed,

is reached in the auxiliary heater heating

terminal 5 of connector A of the control unit

unit (A6), the temperature sensor (A6b1)

(N33) and the switchover valve (Y16) are

signals this to the control unit (N33) as a

energized. The electronics in the control unit

result of its altered resistance, the

(N33) allow a safety switching time of 120 s

electronics of which open the relay (N33c)

to commence. Simultaneously, electronics in

and in turn close the relay (N33d). The

the control unit (N33) close the relay (N33e)

combustion air blower (A6m2) on the

for the glow plug (A6r2) and relay (N33b) for

auxiliary heater heating unit (A6) is now

the circulation pump (A6m1 or A31m1 or

energized via the resistor (A6r1) on the

M13/2); both are operating. The fuel

auxiliary heater heating unit (A6). As a

metering pump (Y23) is also energized

result, the combustion air blower (A6m2)

approx. 30 s later by the electronics in the

only runs at approx. half-speed.

control unit (N33). The voltage is clocked by

At the same time the electronics in the

the electronics in the control unit (N33).

control unit (N33) halve the number of

35 s after switching on, the electronics in the

cycles of the fuel metering pump (Y23) and

control unit (N33) close the relay (N33c),

thus adapt the fuel supply to the lower

which energizes the combustion air blower

demand.

(A6m2) on the auxiliary heater heating unit

Start of combustion interval

(A6).

Once a coolant temperature of approx. 85°C

has been reached in the auxiliary heater

Combustion now commences. The flame

heating unit (A6) the temperature sensor

monitor (A6v1) in the auxiliary heater
heating unit (A6) signals the stabilization of

(A6b1) signals this to the control unit (N33)

combustion to the control unit (N33). The

as a result of its altered resistance.

electronics in the control unit (N33) open the
relay (N33e) and switch off the glow plug

The electronics in the control unit (N33)

(A6r2). The auxiliary heater is now

switch off the fuel metering pump (Y23) and

operating.

switch over from relay (N33d) to relay

Switching on the heater blower

(N33c) so that the combustion air blower

Once the coolant temperature in the

(A6m2) runs at a higher speed.

auxiliary heater heating unit (A6) has risen

After 60 s (after-running) the relay (N33c)

to approx. 55°C, the temperature sensor

opens and thus switches off the combustion

(A6b1) signals this to the control unit (N33)

air blower (A6m2). Circulation pump (A6m1

as a result of its altered resistance. The

or A31m1 or M13/2) and heater blower (M2)

electronics in the control unit (N33) close the

continue running.

relay (N33a) and thus energize the blower

motor (M2).

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End of combustion interval

Switching off with timer in controlled

Once the coolant temperature in the

mode with after-running completed

auxiliary heater heating unit (A6) has

The circulation pump (A6m1 or A31m1 or

dropped to approx. 80°C, the temperature

M13/2) and the blower motor (M2) are

sensor (A6b1) signals this to the control unit

operating.

(N33) as result of its altered resistance, the

By switching off with the timer (N34), the

electronics of which close the relay (N33e)

power to terminal 5 of connector A at the

for the glow plug (A6r2) and start up the fuel

control unit (N33) and to the switchover

metering pump (Y23) 30 s later. The relay

valve (Y16) is interrupted. The electronics in
the control unit (N33) open the relay (N33b)

(N33c) for the combustion air blower (A6m2)

for the circulation pump (A6m2 or A31m1 or

is also closed 35 s after the relay (N33e) by

M13/2) and the relay (N33a) for the blower
motor (M2) and in this way switch them off.

the electronics in the control unit (N33).

At the same time, the operating indicator

Combustion is started. Once combustion has

lamp goes out.

stabilized, this is signalled by the flame

monitor (A6v1) to the control unit (N33). The

electronics in the control unit (N33) open the

relay (N33e) and thus switch off the glow

plug (A6r2). Once a coolant temperature of

approx. 80°C has been reached, the

temperature sensor (A6b1) signals this to

the control unit (N33) and the system

switches to part-load.

Full-load switching (full heating capacity)

Switching is performed automatically when,

because of low outside temperatures, part-

load (approx. half heating capacity) is not

sufficient to maintain the coolant

temperature above 70°C. Once the coolant

temperature has dropped to approx. 70°C in

the auxiliary heater heating unit (A6), the

temperature sensor (A6b1) signals this to

the control unit (N33) by its altered

resistance. The electronics in the control unit

(N33) open the relay (N33d) and in turn

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Switching off at full-load or part-load with

Automatic cutout in the event of a fault in

the timer

controlled mode

When switching off from full or part-load with

If a fault occurs during the controlled mode,

the timer (N34), the power to terminal 5 of

e.g. the temperature cutout (A6f1) is

connector A of the control unit (N33) and to

activated, combustion is interrupted. If the

the switchover valve (Y16) is interrupted.

coolant temperature in the auxiliary heater

The electronics in the control unit (N33)

heating unit (A6) then drops to approx. 80°C,

switch off the fuel metering pump (Y23) and

two start attempts are made, followed by a

combustion ceases. At the same time, the

fault cutout because no combustion has

relay (N33a) opens and the blower motor

taken place. The operating indicator lamp

(M2) is switched off. 60 s later (after-

(green) goes out.

running), the electronics in the control unit

Automatic cutout in the event of a fault in

(N33) open the relay (N33b) for the

part-load or full-load operation

circulation pump (A6m1 or A31m1 or M13/2)

If the temperature cutout (A6f1) is activated

and the relay (N33c) for the combustion air

during part-load or full-load operation, the

blower (A6m2). Circulation pump (A6m1 or

power for the metering pump (Y23) is

A31m1 or M13/2) and combustion air blower

interrupted and the flame goes out. The

(A6m2) are switched off. The operating

flame monitor (A6v1) signals to the control

indicator lamp (green) goes out. During

unit (N33) that the flame has been

after-running at part-load, the electronics in

extinguished. The electronics in the control

the control unit (N33) switch from relay

unit (N33) open the relay (N33a) and the

(N33d) to relay (N33c) so that the

blower motor (M2) is switched off.

combustion air blower (A6m2) runs at high

60 s later (after-running), the electronics

speed.

(N33) open the relay (N33b) for the

Automatic cutout in the event of

circulation pump (A6m1 or A31m1 or M13/2)

unsuccessful combustion

and the relay (N33c) for the combustion air

If no combustion occurs during the safety

blower (A6m2), and both are switched off.

switching period of 120 s after switching on

The operating indicator lamp goes out. For

the heater, the electronics in the control unit

after-running at part-load, a switchover is

(N33) immediately perform an automatic

made from relay (N33d) to relay (N33c) so

repeat start.

that the combustion air blower (A6m2) is

If during the new safety switching time of

running at high speed.

120 s combustion still does not occur, the

electronics in the control unit (N33) switch

off the fuel metering pump (Y23) and 60 s

later (after-running) open the relay (N33b)

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