Air Conditioning System

A/C System Outline Diagram





Air Conditioning System Components
1 - Compressor
2 - Condenser
3 - Receiver
4 - Expansion valve (fitted in the climate control unit on certain variants)
5 - Evaporator
6 - Service connection, low-pressure side
7 - Service connection, high-pressure side

Technical Description
The task of the air conditioning system is to lower the temperature of the cabin to a comfortable level when the outside temperature is high. When the weather is damp, it can also keep the windows free from misting with a low fan speed.

The A/C unit does not produce cold air but leads off heat from the interior. To do this we use a substance or an agent which is cooler than the air, as air always flows from a hot object to a cooler one.

The refrigerant we use for the air conditioning system is a liquid (R134a), which boils and evaporates at a low temperature (-30 °C at normal air pressure). The refrigerant has a constant pressure temperature relationship, which means that if the pressure is changed, the temperature changes as well and vice versa. A condition for this is that the volume remains constant.

This relationship is utilized in the A/C system. By allowing the refrigerant to circulate in a closed system and by changing its pressure, it can be made to change its temperature. If the pressure, and thus the temperature, is changed sufficiently, the refrigerant will start to evaporate (boil). At the pressure prevailing in the low-pressure side of the system, the refrigerant evaporates at about 0 to +4 °C. The process is carried out in the A/C system's evaporator.

One condition for evaporation of the refrigerant is that there is heat available. This heat is taken from the air around the evaporator. When the heat is absorbed by the refrigerant in the evaporator, it cools the ambient air. This is the cool air that flows into the cabin.

The heat that is absorbed by the refrigerant in the evaporator is transported to the engine bay, where it is passed to the atmosphere by an air-cooled condenser.

A/C System Power Supply
When the A/C button is ON, the + 54 power supply goes via fuse 3 to the ventilation fan switch. If the switch is in any position from 1 to 4, power is also supplied to the Integrated Central Electronics (ICE).

The ICE checks the engine temperature and if it is below +126 °C, power is supplied to the anti-frost thermostat. If the temperature in the evaporator is about +5 °C or higher, power is supplied to the engine management system.

The engine control system increases the idling speed and grounds the cable to the three-stage pressure switch. If the pressure in the A/C system is higher than 2 bar but lower than 30 bar, the pressure switch grounds the cable to the A/C relay. Power is supplied from fuse 5 in fuse holder 342A via the A/C relay to the thermo-fuse in the compressor's overheating cut-out. If the temperature in the compressor is lower than +140 °C, power is supplied to the compressor's magnetic coupling.