The condenser on a refrigerator removes heat from a gas coolant and condenses it into high-pressure liquid. Coolant evaporates at low temperatures and low pressure but condenses at high temperature and high pressure; because of this, heat can be transferred from inside the refrigerator to the room. The coolant is contained in a closed system, so the process can be repeated.
The principles of refrigeration are as follows: liquids absorb heat when they are changed to a gas, and gas gives off heat when it is changed to liquid. The refrigerant enters the compressor as a low-pressure gas, where it is compressed and exits as a high-pressure gas. This gas flows to the condenser, where it is condensed to a liquid, and its heat escapes into the surrounding air.
The pressurized liquid then moves to an expansion valve, which limits the flow of the fluid and reduces the pressure of the gas as it exits the expansion valve. The low-pressure gas is then piped into the evaporator and absorbs heat, which changes it from a liquid to a gas.
As a hot gas, the refrigerant then moves to the compressor, where the cycle is repeated. The low-pressure gas is turned into a high-pressure gas and then condensed to a liquid, and so on.