General description of the heater and air conditioner (BMW 5 Series E28)

The heating system consists of a fan and a heat exchanger located inside the heater housing, with hoses connecting the heat exchanger to the engine cooling system and a heater/air conditioning control handle on the instrument panel. Hot engine coolant circulates through the galleries of the heat exchanger while the engine is running. When the heater is turned on, a flap opens, directing air through the heat exchanger, and then the warm air enters the car's interior. The fan switch on the control handle turns on the blower motor, which increases the air flow through the heat exchanger, thus providing an additional heat output, for example, to reduce humidity in the interior, etc.

The air conditioning system consists of a condenser installed in front of the radiator, an evaporator located next to the heater heat exchanger, a compressor mounted on the engine block, a dehydrator accumulator, which includes a high-pressure relief valve, and fittings that connect all of these components together.

The heater fan pushes warm air from the car's interior through the evaporator heat exchanger (operating on the principle opposite to that of a radiator), where the heat of the air is transferred to the system's refrigerant. The liquid refrigerant boils, turning into low-pressure steam, and takes the heat with it as it leaves the evaporator.

Please read the safety precautions at the beginning of the Section Removal and installation the control unit for the heater and air conditioner operating modes, concerning the potential hazards associated with the operation of the air conditioning system.