Heater circuit function

N83.20-2215-79

16 Front heater heat exchanger

21 Radiator expansion tank

22 Water pump

23 Thermostat

24 Radiator

D Coolant feed

E Coolant return

M Engine

A Heater water return

B Heater water supply

C Vent line

The heating circuit is connected to the engine's cooling circuit.

The following components are connected to the cooling circuit:

 Radiator expansion tank

 Water pump

 Thermostat

 Radiator

 Engine

-----------------------------------------------------------------------------------------

The front heater heat exchanger is connected to the heater circuit.

The cooling circuit is divided into the following sections:

 Heater water return

 Heater water supply

 Vent line

 Coolant feed

 Coolant return

-----------------------------------------------------------------------------------------

During the warm-up phase and normal engine operation, coolant is delivered to the engine coolant pipes by the water pump via the coolant feed line. The coolant is heated up in the engine coolant pipes. The thermostat remains closed until the coolant reaches a certain temperature. When the thermostat is closed, a small quantity of coolant flows over the heater water feed line to the front heater heat exchanger and from there over the heater water return line back to the coolant feed line. The rest of the coolant flows from the closed thermostat over the coolant return line to the radiator and from there over the water pump back to the coolant feed line. If the coolant reaches a specific temperature, the thermostat opens and a specified volume of coolant is pumped over the heater water feed line to the front heater heat exchanger and from there over the heater water return line back to the coolant feed line.

A fixed quantity of coolant is also delivered to the radiator via the coolant return line, from where it is returned to the coolant feed line via the water pump.

The radiator expansion tank compensates for any possible coolant loss in the coolant circuit via the coolant feed line and keeps the heated coolant at a constant pressure.

Similarly excess coolant flows from the radiator over the vent line back into the radiator expansion tank.