Heater circuit function - GF83.20-P-2003MCU

MODEL 451.3/4 

Fig 1: Heater Circuit Function Diagram

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Function 

The coolant pump pumps cold coolant through the engine. There, the coolant absorbs the engine heat and then flows over the thermostat to the coolant pump (small coolant circuit).

If the engine has reached its operating temperature, the thermostat opens the large coolant circuit. This subdivides immediately after the thermostat into the cooling circuit and the heating circuit.

In the heating circuit, the coolant flows to the heater heat exchanger via the heating circuit coolant feed pipe. The air flowing through the heater heat exchanger is warmed up in the process and routed into the vehicle interior.

Next, the coolant flows from the heater heat exchanger to the expansion reservoir and from there to the cooler or back to the coolant pump via the coolant return line.

In the cooling circuit, the coolant flows from the thermostat via the coolant feed pipe for the cooling circuit to the cooler and from there onward to the coolant pump via the coolant return line.