P83.70-2686-04
Schematic diagram
Coolant
A6 STH and heater booster unit
G2 Water-cooled generator
N33/2 Heater booster control module
As of approx. 06/99 all model 210 and 220 vehicles with diesel engines and Common-Rail injection have 3 new heater booster systems connected in series (see figure).
The generator (G2) is water-cooled. It is incorporated directly in the engine coolant circuit. The engine coolant is used to cool the generator and at the same time the generator coolant is also heated up by up to 1.5 kW by the generator.
The familiar combustion heater booster produces approx.
5.2 kW heat output at full load. It is switched on when the outside temperature is approx. < 3°C and the coolant temperature is below approx. 76°C. It is switched off when the coolant temperature rises above this value or the outside temperature rises above approx. 8°C. With regard to the outside temperature it is switched on and off by a bimetal switch which monitors the coolant temperature inside the heater unit.
The electric heater booster is switched on and off by the engine control module. If the coolant temperature is the same as the outside temperature it is switched on at approx. 8°C. The engine control module obtains this information via the CAN. So that the heater booster does not overload the battery, it receives a generator load signal from the generator and controls the output so that the generator is fully utilized but no current is drawn from the battery.
Automatic switching on of the combustion heater booster and electric heater booster can be prevented by a switch under the ashtray flap. The LED in the switch comes on when the heater boosters are deactivated.