The refrigerant must be cycled repeatedly. All HVAC systems use the same cycle of compression, condensation, expansion, and evaporation in a closed loop. The same refrigerant is used to absorb the heat from one area, thus cooling this area, and transferring this heat and expelling it outside.

• The refrigerant comes into the compressor as a low-pressure gas, it is compressed and then moves out of the compressor as a high-pressure gas.
• The gas then flows to the condenser. Here the gas condenses to a liquid, and gives off its heat to the outside air.
• The liquid then moves to the expansion valve under high pressure. This valve restricts the flow of the fluid, and lowers its pressure as it leaves the expansion valve.
• The low-pressure liquid then moves to the evaporator, where heat from the inside air is absorbed and changes it from a liquid to a gas.
• As a hot low-pressure gas, the refrigerant moves to the compressor where the entire cycle is repeated.