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A/C system

A/C system

The function of the air conditioning is to lower the cabin temperature to a comfortable level at high exterior temperatures as well as to provide a stable temperature for the ACC system to adjust against. The A/C unit also decreases the humidity of the cabin air during damp weather, without increasing the cabin temperature and thus contributes to de-misting the windows at low fan speed.

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 constant.

By having the refrigerant circulate in a closed system and changing its pressure, temperature change can be achieved. If the pressure changes sufficiently, and accordingly the temperature as well, the refrigerant begins to evaporate (boil). For the pressure that exists on the low pressure side, the refrigerant evaporates at approximately 0 to +4°C. The process occurs in the A/C 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 handling refrigerant, see Draining and filling of refrigerant .

Cooled glove box

All cars with A/C have a hose that runs from the heating and ventilation unit to the glove box. With a control at the back at the glove box, it is possible to open/close off the hose and select whether or not the glove box and its contents are to be cooled.