Compressor

The compressor is the heart of the AC system. It compresses and circulates the refrigerant around the system. Low pressure refrigerant is drawn into one side of the pump, and expelled as a high pressure vapour. During this process, the temperature of the vapour rises significantly. The compressor is usually driven by a belt attached to either the engine directly, or the alternator.

Condensor

Once compressed, the refrigerant vapour is at a high temperature, and therefore not too useful for cooling the car. The condensor changes the vapour into a liquid, a reaction which causes a large drop in temperature. The condensor is like the radiator on the engine, and is normally located at the front of the engine bay.

Evaporator

The evaporator receives the cold refrigerant, and uses it to cool the air in the cabin of the car. It is usually located in the heater air intake. Some vehicles have more than one evaporator to serve different areas inside the cabin.

Expansion Device

The expansion device comes in many forms. It can be a brass internally or externally equalised valve, a block type valve or an orifice tube (the latter being part of an accumulator type air conditioning system). Expansion Devices have an inlet and an outlet which separates the high side of the system from the low side. A small restriction in the valve allows only a small amount of refrigerant to pass through it into the Evaporator. The amount of refrigerant passing through the valve depends on the Evaporator temperature. The most common reasons for failure are contamination, moisture and lack of regular servicing.

Drier

This is where some AC systems differ. In an expansion valve system, the drier is known as a receiver, and in a fixed-orifice tube system, it is an accumulator. A receiver removes impurities from the system, absorbs moisture, and ensures that only liquid refrigerant reaches the expansion valve. In contrast, an accumulator prevents liquid refrigerant from entering the compressor.