A/C System Overview

Function And Operation Of Air Conditioning.
- The air conditioning system is part of the climate system. It enables the interior temperature to be lowered in relation to the outside (ambient) temperature and also dries the interior air so that the windows are demisted more quickly.

- The system does not create cold air but extracts heat from the passenger compartment. This requires the use of a medium at a lower temperature than the air since heat always flows from a hotter to a colder body.

- The medium used is a liquid refrigerant:
- in earlier models chlorofluorocarbon R12
- in models from 1993 on fluorine R134a.

- The ability of the medium to absorb and emit so much heat is due to the fact that it boils (evaporates) at low temperature -30 °C (-22 °F) at normal atmospheric pressure. The medium is then returned to liquid form (condensed) as it flows around the circuit.

- The relationship between the refrigerant pressure and temperature is constant; in other words, if the pressure changes, so does the temperature, provided that the volume is constant. Operation of the system is based on this condition. The temperature of the refrigerant can be varied and the medium made to boil (evaporate) by allowing it to circulate in a closed system and varying its pressure and volume. At the normal system pressure of approx. 1.7 - 3.2 bar (24.7 - 46.4 psi), the medium boils at about 0 to +4 °C (32 - 39.2 °F).

- The availability of sufficient heat is essential to boiling. This heat is drawn from the air around the evaporator in which boiling occurs and the surrounding air is cooled as the refrigerant absorbs the heat. It is this cooled air which is blown into the passenger compartment by the blower. The heat absorbed by the refrigerant in the evaporator is discharged to the air in the engine compartment by the condenser, which is cooled by the natural air flow and/or by the engine cooling fan (FC).

- The air conditioning system is of the compressor type; in other words, a compressor is used to "pump" the refrigerant through the various components in the circuit.