Heater circuit function

P20.00-0368-06

1 Screw cap (one-stage)

2 Coolant expansion reservoir

3 Radiator

4 Coolant thermostat (in engine at operating temperature position)

5 Coolant pump

6 Bypass

8 Heating system heat exchanger

A Coolant return flow

B Coolant infeed

C Filling ventilation (functional only when screw cap is removed)

D Short-circuit mode temperature

< 87 °C
coolant flow via engine and passenger compartment heating only

E Mixed-mode temperature

> 87 °C < 102 °C
thermostat opens. Commencement of flow through radiator

F Cooling mode temperature > 102 °C
thermostat opened, full flow through radiator

Function

The coolant pump (5) pumps cold coolant through the engine. The coolant absorbs the engine's heat and becomes heated. The heated coolant is then conducted through the heat exchanger (8). The air passing by at the heat exchanger is heated and conducted into the vehicle interior.

Via the coolant return (A), the coolant returns back to the coolant pump (5).

By far the greater percentage of the coolant does not flow through the heater, but from the engine (M) to the coolant thermostat (4). Depending on the water temperature, this conducts the water through the radiator (3) or directly to the coolant pump (5).