The compressor is the heart of the cooling cycle. The cycle begins when the compressor draws in cool, low-pressure refrigerant gas from the indoors. The motor-driven compressor’s sole function is to "squeeze" the refrigerant, raising its temperature and pressure so that it exits the compressor as a hot, high-pressure gas.
The compressor pushes the hot gas to the finned condenser coil in the outdoor side of the air conditioner where fans blow cool outside air over the coil and through the fins, extracting the heat from the refrigerant and transferring it to the outside air.
When enough heat has been extracted from the refrigerant, it condenses into a warm liquid that passes under high pressure to an expansion valve that turns the refrigerant into a cool, low-pressure liquid. The refrigerant goes from the expansion valve to the finned evaporator coil located in the indoor or room side of the air conditioner unit.
When the refrigerant enters the evaporator coil where the pressure is much lower, it is chemically compelled to evaporate into a gas. This process requires heat, which comes from the room's warm air being blown over the evaporator coil by another fan. As room heat is transferred to the evaporating refrigerant, the room's air grows cooler. The refrigerant, now back to a cool, low-pressure gas, is drawn back into the compressor to continue the cycle.