GF83.70-D-0003H Auxiliary Heater (ZHE) - Function

GF83.70-D-0003H Auxiliary Heater (ZHE) - Function

- with CODE (H11) Warm air auxiliary heater

The auxiliary heater heating unit is the main component of the auxiliary heater (ZHE) system and exists in the following 2 versions:
- AIRTRONIC D2S, for model 906.2 with engine OM642 or engine OM646
- AIRTRONIC D4S, for model 906.6/7 with engine OM642 or engine OM646

One function requirement is that there is no undervoltage or overvoltage.

Undervoltage is present when voltage < 10.5 V. Overvoltage is present when voltage > 16 V.

The auxiliary heater heating unit is located in the seat frame of the front passenger seat or double front passenger bench seat with code (S23) Two-seater front passenger seat for model 906.2, and on the left-hand side on the vehicle underfloor at C-pillar level for model 906.6/7. The auxiliary heater heating unit is used to heat the rear area when the vehicle is at a standstill and during driving. The voltage is supplied by the battery (G1) or additional battery (G1/2), with code (E28) Additional battery 12 V 88 Ah.
The heater is operated using the heater timer (N34) which is located in a "DIN slot" in the headliner of the driver compartment above the DBE control unit (N70), with code (LD0) Dome lamp with reading lamp on the driver/front passenger side, or in the front dome lamp with switch (E15/1).

The warm air is dispensed via a warm air nozzle behind the seat frame of the front passenger seat or double front passenger bench seat with code (S23) Two-seater front passenger seat for model 906.2, and via a warm air nozzle in the left-hand side paneling behind the driver seat for model 906.6/7. The temperature of the interior is controlled via the interior temperature sensor (S98b1) with code (HH9) Regulated air conditioning, (Tempmatic), via the rear interior air temperature sensor ventilation blower (M9/1) with code (HH7) Additional air conditioning in rear or with code (H08) High-performance air conditioning, or by means of an external temperature sensor.
The auxiliary heater heating unit consists of the following components:
- Heat exchanger
- Burner insert with burner tube
- Hot air auxiliary heating control unit (N33/6)
- Overheating sensor (N33/6b1)
- Flame sensor (N33/6b2)
- Blower motor (N33/6m1) of auxiliary heater combustion air blower
- Glow plug (N33/6r1)

The auxiliary heater system also requires the metering pump (Y23/4) to start heater operation.

Function sequence of auxiliary heater heating unit
The auxiliary heater heating unit is switched on directly via the heater timer or by preselecting a time. The warm air auxiliary heater control unit integrated into the auxiliary heater heating unit then starts heater operation. The rotational speed of the blower motor of the auxiliary heater combustion air blower and the metering pump are regulated accordingly during the starting procedure. The metering pump takes fuel from the vehicle fuel tank and feeds it through the burner insert into the burner tube. There, together with the combustion air fed in by the blower motor of the auxiliary heater combustion air blower, it forms an ignitable mixture which is then combusted in the burner tube.

The combustion heat is now available for heating purposes. Air then flows through the jacket of the heat exchanger with the aid of the blower motor of the auxiliary heater combustion air blower. The air that is heated at the heat exchanger is then sent back into the interior. The desired interior temperature is set on the heater timer.

The thermostatic control of the interior temperature is performed by the warm air auxiliary heater control unit integrated into the auxiliary heater heating unit in combination with the interior temperature sensor with code (HH9) Regulated air conditioning (Tempmatic), the rear interior air temperature sensor ventilation blower with code (HH7) Additional air conditioning in rear or with code (H08) High-performance air conditioning, or by means of an external temperature sensor.