Heater circuit function

D83.20-1128-79

The heating circuit is connected to the engine's cooling circuit. The following components are integrated in the coolant circuit:

 Coolant expansion reservoir

 Coolant pump

 Coolant thermostat

 Radiator

 Motor

 Heater booster (with CODE HZ9 (Heater booster, diesel))

The heater heat exchanger, circulation pump and water cycle valve are components integrated in the heater circuit.

The cooling circuit is divided into the following sections:

 Heater water return

 Heater water supply

 Vent line

 Coolant feed

 Coolant return flow

 Vent line

In the warm-up phase and in normal operation of the engine, the coolant is delivered by the coolant pump via the coolant feed to the coolant guides of the engine. The coolant is heated in the coolant guides for the engine and heater booster (with CODE HZ9 (Heater booster, diesel)).

The coolant thermostat remains closed as long as a certain coolant temperature has not yet been reached. When the coolant thermostat is closed, a small amount of coolant reaches the heater heat exchanger via the circulation pump. This coolant quantity is also regulated by the water cycle valve, depending on the actuation by the automatic air conditioning control and operating unit (A81).

From the heater heat exchanger, the coolant returns to the coolant feed via the heater water return. The rest of the coolant returns from the closed coolant thermostat via the coolant return to the radiator and from there via the coolant pump back into the coolant feed.

Once the coolant has reached a certain temperature, the coolant thermostat opens and a fixed quantity of coolant is supplied to the heater heat exchanger by means of the circulation pump integrated in the heater water feed. This coolant quantity is also regulated by the water cycle valve, depending on the actuation by the automatic air conditioning control and operating unit. The coolant is delivered back into the coolant feed from the heater heat exchanger via the heater water return. Also, a fixed quantity of coolant is delivered via the coolant return to the radiator and from there via the coolant pump back into the coolant feed.

The coolant expansion reservoir compensates for any coolant fluctuations in the cooling circuit through the coolant feed and keeps the heated coolant at a constant pressure. Excess coolant also returns from the radiator via the vent line into the coolant expansion reservoir.