In the diagram above, the compressor (1) compresses the refrigerant vapor and moves it towards the condenser. The heat of compression raises the temperature of the refrigerant vapor causing it to be a high pressure superheated vapor. As this refrigerant moves into the condenser (2), the condenser rejects the heat in the refrigerant, causing it to change state and condense into a high pressure, high temp liquid.
As the refrigerant passes through the metering device (3), its temperature, pressure and state change once again. Some of the low pressure liquid refrigerant instantly boils off forming “flash gas”. As this mixture of liquid and gas pass through the evaporator (4) heat is absorbed and the remaining liquid refrigerant changes it state back into a vapor. At the outlet of the evaporator 100% of the low pressure vapor flows back through the suction line to the compressor.
Specially colored coils on the window air conditioner below aid the student in visualizing and understanding the flow of the refrigerant, and the different changes in the state of the refrigerant as it traverses through the system.