Heating Circuit, Basic Function - GF83.20-P-1002A

Model All (4xWD) 

Model All (CAR) 

Courtesy of MERCEDES-BENZ USA

Example illustration showing heating circuit on vehicles with combustion engine (schematic representation) 

Overview 

This document contains information on:

• General 
• Function requirement 
• Function 

General 

The heating circuit is used to heat the vehicle interior at low outside temperatures. It is coupled to the refrigerant circuit via capacitor and is operated as a heat pump heater.

Function requirements 

• Engine running

Function 

The following component parts are integrated into the heating circuit:

• Coolant circulation pump (5)
• Heater core (6)

The coolant pump (12) pumps coolant through the engine oil heat exchanger (3) and the engine (8). The coolant flows from the engine oil heat exchanger (3) through the coolant thermostat (7) and from there into the radiator (13) or back into the circuit upstream of the coolant pump (12). In the engine (8), the coolant absorbs the engine heat and heats up. Some of the heated coolant then flows through the heater core (6), where the heat is dissipated to the blowby air. The other part of the heated coolant flows through the exhaust gas turbocharger (11) and from there back into the circuit upstream of the coolant pump (12) and is thus cooled directly. Downstream of the heater core (6), the coolant circulation pump (5) delivers the coolant to the stationary heater (2), then the switchover valve (4) divides the coolant. One part flows back into the circuit upstream of the heater core (6), while another part flows back into the circuit upstream of the coolant pump (12). The transmission oil cooler circulation pump (10) pumps the coolant through the transmission oil heat exchanger (9) back into the circuit upstream of the coolant pump (12).

The coolant circulation pump (5) pumps the coolant during engine standstill (e.g. for residual heat utilization) and supports the coolant pump (12) at low engine speeds. It is actuated by the climate control, control system to match the given load.

The coolant quantity is also regulated by a coolant expansion reservoir (1).