0400 - Function description: auxiliary heater A. General Models 124, 126, 201

83-400

Function description

A. General

The auxiliary heater is connected to the

The auxiliary heater must not be operated in

coolant circuit of the engine. It can be

enclosed areas with no exhaust extraction

switched on when the car is parked or when

facility, even with the programmed heating

driving if a higher heating capacity is

mode. The auxiliary heater should be

required.

switched off at filling stations.

The auxiliary heater is designed to heat the

If the power for the timer is interrupted for

passenger compartment and to defrost the

more than 3 s, the time display flashes when

car windows. The cold engine is also

one of the buttons 1 - 3 has been pressed.

preheated by means of the coolant which

The time should then be reset.

assures more reliable starting of the engine

even at low outside temperatures.

Timer (1st version, model 201.02 up to
approx. 03/85)
The auxiliary heater is switched on and off

with the timer. This is installed in the center

console. The heater starting point can be

preselected up to 24 hours in advance.

Pushbutton for calling up current time display

Pushbutton for programmed heating

Pushbutton for instant heating

Pushbutton for slow setting of clock time

Pushbutton for rapid setting of clock time

Programmed heating indicator lamp (yellow)

Operating indicator lamp (green)

Clock time display

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Instant heating operation
Press pushbutton (3). The auxiliary heater

switches on and the green operating indicator

lamp (7) comes on. In the instant heating

mode, the automatic operating time of max.

59 minutes is indicated in the display (8). The

automatic operating time can be reduced by

pressing pushbuttons 4 and 5.

The auxiliary heater can be switched off with

pushbutton (3) before the expiry of the

automatic operating time.

When the instant heating mode is switched
off/on (pushbutton 3) during the maximum
operating time of 59 minutes, the remaining
operating time is indicated in the display (8)
each time the heater is switched on, always
rounded up or down to 9 minutes, i.e. the
display shows 9, 19, 29 minutes, etc. If the
full operating time (59 minutes) is desired
instead of the remaining time displayed, e.g.
29 minutes, the time in the display (8) must
be set to 00. This switches off the auxiliary
heater. It is then necessary to press
pushbutton (3) (on). The operating time is
now 59 minutes.

Operation with programmed heating
Press pushbutton (2), the yellow programmed

heating indicator lamp (6) comes on. The

heater is switched on automatically at the

selected time and the green operating

indicator lamp (7) also comes on. Automatic

operating time 1 hour.

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Pushbutton for calling up current time display

Pushbutton for switching on/off programmed

heating

Pushbutton for switching on/off instant heating

Pushbutton for slow setting of clock time

Pushbutton for rapid setting of clock time

Programmed heating indicator lamp (yellow)

Operating indicator lamp (green)

Clock time display

Timer (2nd version, model 201.02 as of
approx. 04/85)
Revised functions

a) Forward and reverse (buttons 5 and 7)

for setting time of day and cut-in time.

b) The automatic operating time for instant

heating (button 4) is not displayed. It is 1

hour.

c) One cut-in time can be stored for

programmed heating with each of buttons (1)

and (2). If the programmed heating mode is

switched on with button 1 or 2, the yellow

programmed heating indicator lamp (8)

comes on. The number of the button pressed

appears in the display (8) and the cut-in time

for 20 seconds. Once the auxiliary heater is

operating, only the green operating indicator

lamp (9) is illuminated.

1/2 Pushbutton for programmed heating
3

Pushbutton for displaying current time

Pushbutton for instant heating

Pushbutton for reverse setting of time of day and

cut-in time

Time display

Pushbutton for forward setting of time of day and

cut-in time

Yellow programmed heating indicator lamp

Green operating indicator lamp

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Control unit
The control unit (N33) houses relays and

time switches which automatically control the

operating sequence in combination with the

temperature sensor of the auxiliary heater

heating unit (A6).

Heater
The fuel-air mixture is burnt in the heater and

thus heats the coolant in the water jacket.

The components listed in the illustration are

part of the heater assembly and perform the

functions described below.

Auxiliary heater unit

A6b1

Temperature sensor

A6f1

Temperature cutout

A6m1

Circulating pump

A6r1

Combustion air blower preresistor

A6m2

Combustion air blower

A6r2

Glow plug

A6v1

Flame monitor

Flame monitor (in heater)
The flame monitor is a light-sensitive

component which monitors combustion. If

combustion stops, the flame monitor signals

this to the control unit and the control unit

switches off the heater (malfunction).

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Glow plug (in heater)
The glow plug produces the heat necessary

for starting and is switched off by the flame

monitor via the control unit (N33) after

combustion has stabilized.

Temperature sensor (in heater)
The temperature sensor is a resistor (PTC)

which alters its value in response to

temperature. Its resistance increases as

temperature increases. Switching on the

heater blower and operation of the heater

(full or half heating capacity or combustion

interval) is controlled by the temperature

sensor via the control unit (N33).

Temperature cutout (in heater)
1st version
The temperature cutout is an overheating

protection. At a temperature > 140°C, the

fuse in the temperature cutout blows,

interrupting the power for the fuel metering

pump. This results in full shutdown of the

heater.

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Resettable temperature cutout (in heater)
2nd version

The temperature cutout is an overheating

protection. At a coolant temperature > 117°C,

the resettable temperature cutout is

activated, interrupting the power for the fuel

metering pump. This results in fault shutdown

of the heater.

Combustion air blower (on heater)
The combustion air blower delivers the
quantity of air required for mixture
preparation. Control is by means of the
temperature sensor via the control unit (N33).

Circulation pump (on heater)
The circulation pump ensures coolant
circulation. It operates when the auxiliary
heater is switched on, and on models
124.061, 124.0 up to approx. 09/92, (except
model 124.034), models
124.120/128/133/188/193/3 up to approx.
01/93, models
124.125/127/130/180/185/190/2, models
126.02 and 201 even when the ignition is
switched on if the vehicle heating is in
heating mode.

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Circulation pump - models 124.034/036
The circulation pump ensures coolant
circulation. It operates when the auxiliary
heater is switched on.

Model 124.034

Model 124.036

Heating system supply unit (A31)
Model 124.0 as of approx. 10/92 (excluding
models 124.034/036/061),
models 124.120/128/133/188/193/3 as of
approx. 02/93, models 124.126/131/186/191
No circulation pump is fitted to the auxiliary
heater heating unit (A6). The coolant is
circulated by actuating the production
circulation pump (A31m1) which is integrated
in the heating system supply unit (A31).

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Resistor on the heater
At partial load operation, the resistor of the

control unit (N33) is connected upstream of

the combustion air blower so that the

combustion air blower operates only at

approx. half speed.

Fuel metering pump (1st version for
model 124 up to approx. 08/89, on model
201 up to approx. 08/88)
The fuel metering pump delivers the quantity
of fuel necessary for combustion from the
fuel tank to the heater. The pump is
controlled by the control unit (N33).

Fuel metering pump (2nd version on
model 124 as of approx. 09/89, on model
201 as of approx. 09/88)
The function of the fuel metering pump is

identical to the 1st version. The operating

range for fuel induction has been increased,

enabling the pressure reducer on diesel

models to be deleted.

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Pressure reducer
The pressure reducer (arrow) on diesel

models is connected upstream of the fuel

metering pump (1st version), as the pressure

at the fuel extraction point is too high.

Exhaust silencer (1st version)
The exhaust silencer (arrow) muffles the

combustion noise and vents the exhaust gas

into the atmosphere.

Exhaust silencer (2nd version)

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Electrical fuses
The auxiliary heater is protected against

overload and short-circuit with two fuses.

Glow plug

Auxiliary heater control

Fuse

16 amps

8 amps

Thermostat
Models 124.034/036
The thermostat has three functions in

conjunction with the auxiliary heater coolant

circuit.

Up to approx. 55°C coolant temperature, the
coolant supply from the engine to the
auxiliary heater heating unit (A6) is shut off
and the coolant in the engine does not heat
up.

Between 55°C and 65°C coolant
temperature, the thermostat starts to open
and regulates the coolant supply from the
engine to the auxiliary heater heating unit
(A6). Thus the coolant in the engine is also
heated up.

Above 65°C coolant temperature in the
engine, the thermostat is fully open and the
coolant is still only supplied to the auxiliary
heater heating unit (A6) from the engine.
The engine is therefore fully incorporated into
the coolant circuit.

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