Auxiliary Heater, Function - GF83.70-D-0004TSA

Model 907 

with code H12 (Auxiliary hot-water heater) 

Model 907 

with code HZ9 (Heater booster) 

Function of hot-water auxiliary heater 

The hot-water auxiliary heater augments the vehicle's air conditioning system, and it has a heat boosting, stationary heater and stationary ventilation function. The auxiliary heating also heats the engine coolant thereby conserving the engine and enabling it to save fuel during the warm-up phase. The stationary heater heats the air in the vehicle interior to the set temperature. It is not dependent on the heat output by the engine while it is running.

The auxiliary heating is directly operated with the vehicle's fuel. This is why the fuel tank has to be filled over the reserve level so that the auxiliary heating functions. The auxiliary heating automatically adapts its operating mode to changes in the outside temperature and the weather conditions. Therefore, it can happen that the auxiliary heating switches over from the ventilation into heating mode or from the heating mode to the ventilation mode.

When the engine is running, the stationary ventilation is inactive. The auxiliary heating is automatically switched off after a maximum period of 50 minutes. In the "stationary ventilation" operating mode, the air in the vehicle interior cannot drop below the outside temperature. The heater booster function supports the vehicle heating system when the engine is running and at low outside temperatures. Operation of the hot-water auxiliary heater burdens the starter battery.

Depending on the equipment installed, the hot-water auxiliary heater is triggered or ended using the following components:

• Push button switch on the control and operating unit for the automatic climate control (N22/2)
• Radio remote control (with code HY1 (Radio remote control for hot-water auxiliary heater))

Activation of the auxiliary heating and therefore the heating mode, requires the fill level of the fuel tank to be > 16 l.