How they work - AC components

Condenser 

A condenser is a heat exchanger belonging to the vehicle air conditioning system. Its function is to condense the refrigerant in the air conditioning cycle into a liquid, by exchanging the heat from the high temperature and high pressure gaseous refrigerant to the cooler outside air. When the refrigerant is liquified, it flows to the receiver dryer.
Similar in structure to the radiator, the condenser has to withstand the high internal pressures (up to 34 bar) typical of air conditioning systems.

Evaporator 

The evaporator vaporises the low pressure and low temperature refrigerant. When vaporising the refrigerant a large amount of heat is required which the evaporator absorbs from the warm air passing over the evaporator fins, thus cooling the passenger compartment. All liquid changes into a gas and flows to the compressor. The process is then repeated again.

Pressure Switches 

The pressure switch (or pressure sensor) is a safety device which protects the refrigerant cycle components from a too high pressure or a too low pressure. Secondly the pressure sensor sends the signal to a control unit, which uses the signal to calculate the correct variable displacement of the electronic controlled variable type compressor.

Receiver Driers 

The receiver drier will store the refrigerant until the evaporator requires it, ensuring that only liquefied refrigerant flows to the evaporator. Secondly the refrigerant is filtered and dried. After separation of gas and liquid, liquid refrigerant flows to the expansion valve.

Expansion Valves 

The expansion valve injects the refrigerant into the evaporator, changing the refrigerant from a high pressure and high temperature liquid, into a low pressure and low temperature liquid and gas mixture.

The expansion valve adjusts the refrigerant quantity according to the temperature of the superheated gas at the evaporator outlet. As a result, conditions are maintained under which the change of the refrigerant state (evaporation) is completed and only gas will flow to the compressor.

If the A/C system is not emitting cooled air, or only a little cool air, the expansion valve could be clogged or defective. This type of symptom or fault should always be investigated by an A/C Service Repair professional, because in some conditions it can cause liquid lock in the compressor and end up becoming very costly for the car owner. 

Accompressor Scematic UK