Air Conditioning System

A/C system

The function of air-conditioning in a car is to lower the cabin temperature to a comfortable level when outside temperatures are high and to supply the ACC system with a stable temperature on which to regulate the set cabin temperature. The system also reduces humidity in the cabin during damp weather without increasing the cabin temperature and can therefore keep windows free from mist at low fan speeds.

The A/C system does not produce cold air, but removes heat from the incoming or recirculated air. This is accomplished by using a substance, or agent, which has a lower temperature than the air, because heat is always transferred from a warmer object to a colder one.

The agent, refrigerant, that is used boils and evaporates at a low temperature. The ratio pressure/temperature of the refrigerant is constant, which means that if the pressure is changed, the temperature changes and vice versa. This is true as long as the volume is held constant.

By allowing the refrigerant to circulate in a closed system and changing the pressure, its temperature can be changed. If the pressure, and therefore the temperature, is changed to a sufficient degree the refrigerant will start to evaporate (boil). At the pressure which is present on the system's low pressure side, the refrigerant evaporates at approx. 0 - +4 °C. This process takes place in the A/C system evaporator.

In order for the refrigerant to evaporate, there must be heat. This heat is taken from the air surrounding the evaporator, making the surrounding air colder. It is this cold air that is led into the cabin.

The heat that is absorbed by the evaporator is conveyed to the engine bay, where it is transferred to the surrounding air via an air-cooled condenser.

Refrigerant
The refrigerant is a fluid called R134a. R134a boils and evaporates at a temperature of approx. -30°C at normal atmospheric pressure. When the refrigerant evaporates in the evaporator, it absorbs heat from the surrounding air. The cooled air is then led into the cabin.

R134a is chlorine-free refrigerant. It does not affect the ozone layer in the atmosphere.

For information on Draining and Filling of Refrigerant, see "Service and Repair."
Service and Repair

Cooled glove box
On all cars with A/C, there is a hose leading from the climate housing to the glove box. With a control at the back of the glove box, it is possible to open/close this hose and select whether or not the glove box and its contents are to be cooled.