Operation CHARM: Car repair manuals for everyone.

Air Conditioning System



The function of the air conditioning system in the car is to reduce the temperature inside the car to a comfortable level when the outside temperature is high.

In wet weather, the AC system can also keep the windscreen and side windows demisted, with the fan running at low speed, even under the most difficult conditions.

The AC system does not produce cold air but extracts heat from the air inside the car.

Since heat always flows from a hotter body to a cooler one, a medium whose temperature is lower than that of the air inside the car is used to carry the heat away.

The medium used is a liquid (Freon or refrigerant R12) which boils and vaporizes at a low temperature (-30°C at atmospheric pressure).

At a given volume of refrigerant, there is a constant relationship between pressure and temperature, which means, for instance, that if there is a change in pressure there will be a corresponding change in temperature. It is this property that is utilized by the AC system.

The refrigerant is circulated round a closed system and a reduction in the pressure in the system raises the temperature of the refrigerant, causing it to boil (vaporize). At the pressure prevailing in this system, the refrigerant vaporizes at an approximate temperature of 0-4°C (32-39°F).

However, to change its state from a liquid to a gas, the refrigerant must be supplied with heat. This heat is taken from the air surrounding the evaporator in which the stated change takes place. Because this heat is being absorbed by the refrigerant, the surrounding air becomes colder. This same chilled air is then blown into the car by the ventilation fan. The heat absorbed by the refrigerant inside the evaporator is carried to the engine compartment where it is dissipated in the air by a condenser, which is cooled by the ram air and/or the cooling fan.

The AC system is of the compressor type, which means that a compressor forces the refrigerant to circulate through the various system components.

Cars are at present fitted with two different systems which mainly differ in their control function. During the 1980 models, the "VIR" system was replaced by the "Cycling Clutch" system. The Cycling Clutch system was produced in two versions, which differ on the 1980 and 1981 models. These are factory-fitted. A third version - the Clarion Cycling Clutch system - has also been fitted to cars.





Air Conditioning Unit
1 Compressor
2 Condenser
3 VIR assembly (suction throttling valve, expansion valve, filter)
4 Evaporator
5 Service outlet, low pressure
6 Service outlet, high pressure
7 Expansion valve
8 Receiver shell





The Clarion Cycling Clutch system
1 Compressor
2 Condenser
3 Evaporator
4 Expansion valve
5 Filter/dryer receiver