Main Air Conditioning

1 Desiccant container
2 Evaporator
3 Condenser
4 Compressor

The function of air conditioning in a car is to lower air temperature in the cabin to a comfortable level when outside temperatures are high.

In humid weather, the system can also keep windscreen and windows free from mist at low fan speeds, even in difficult conditions.

The air conditioning does not produce cold, but removes heat from the car cabin.

In order to conduct heat away from the cabin, a refrigerant is used which has a lower temperature than the air as heat always moves from a warmer object to a colder one.

The refrigerant used is a fluid, R134a (R12 in older year models), which boils and evaporates at low temperature (about -30° C (-22° F) at normal atmospheric pressure).

The refrigerant has a constant ratio between pressure and temperature meaning that if, for example, pressure is changed, temperature also changes. This applies as long as volume is constant.

This relationship is used in the air conditioning by allowing the refrigerant to circulate in a closed system and changing its pressure so that temperature changes and it boils (evaporates). At system pressure, the refrigerant boils at about 0° - 4° C (32 - 39° F).

In order for the medium to boil, heat must be available. This heat is taken from the air around the evaporator in which boiling takes place. When heat is absorbed by the refrigerant, the surrounding air becomes colder. It is this cold air which is blown into the cabin by the heating and ventilation unit fan. The heat which is absorbed by the refrigerant in the evaporator is. transported to the engine compartment where it is transferred to the air by a condenser which is cooled by the air blowing through it and/or the electric radiator fan.