Air Conditioning: Refrigerant

In order to remove heat from the passenger compartment a medium that has a lower evaporating temperature than air is used, because heat will always move from a hotter body to a cooler body. The medium that is used is refrigerant R134a.

R134a is a gaseous fluorocarbon. It is chlorine free and does not damage the ozone layer. However, R134a is still environmentally hazardous as it contributes to the greenhouse effect. It is therefore important that all service work is performed by trained personnel.

R134a retains its gaseous form at normal atmospheric pressure, and only condenses if it is cooled down to below -26 °C.

R134a has the following properties:

• can only be mixed with synthetic PAG oils (polyalkyline glycol) and not with mineral oils
• does not affect metals
• affects some types of plastic, so only special seals that are intended for R134a should be used
• is not explosive
• is odorless
• is not toxic in low doses
• effectively absorbs moisture
• is not flammable
• is heavier than air in gaseous form.

By allowing the refrigerant to circulate in a closed system and changing its pressure and volume, you can change its temperature to make it boil (vaporize). At the working pressure prevailing in the system's low-pressure side, approximately 170 - 320 kPa (1.7 - 3.2 bar), the refrigerant boils at about 0 to +4 °C.

A prerequisite in order for the refrigerant to boil is that heat is available. The heat is taken from the air around the evaporator in which the boiling occurs. When the heat is taken up by the refrigerant the surrounding air becomes colder. It is this cold air that is blown out into the passenger compartment by the climate system's fan. The heat taken up by the refrigerant in the evaporator is transported to the engine compartment where it is discharged to air by the condenser. The condenser is cooled by the speed wind and the engine cooling fan.