How Vehicle Air Conditioning Works.


High Pressure Side There are two "sides" to the air conditioning system, a low pressure side and a high pressure side. On the high pressure side, low pressure R134a vapour entering the compressor is compressed to become high pressure/temperature R134a vapour. This is then circulated along with lubricant oil to the condenser. As the high pressure/temperature vapour travels through the condenser, heat is released to the cooler ambient air passing over the condenser tubes condensing the vapour into a liquid. This high pressure/temperature liquid then travels through the filter drier onto the expansion valve where a small variable orifice provides a restriction against which the compressor pushes.

Low Pressure Side On the low pressure side, suction from the compressor pulls the high pressure/temperature liquid R134a through the small variable orifice of the TX valve and into the low-pressure side of the A/C system. The R134a is now a low pressure/temperature vapour where heat from the cabin being blown over the evaporator coil surface is absorbed into the colder low pressure refrigerant The R134a is then pulled through the evaporator and into the compressor. The A/C cycle begins again as the R134a vapour is compressed and discharged under pressure.

AC System SummaryTo summarise, R134a in the LOW-PRESSURE side is COLD and can absorb large quantities of heat from the air moving over the evaporator. R134a in the HIGH-PRESSURE side is HOT and the cooler ambient air moving over the condenser can absorb the heat from it.