The purpose of the evaporator is to expand liquid freon in the A/C system to a gas. Once liquid freon leaves the expansion valve, it travels to the evaporator where, once inside the coils, it is allowed to expand further and "evaporate" into a gas. This "evaporating" process requires heat to occur, and this heat is taken from the air that is pulled around the evaporator coils by the blower motor. As the evaporating freon absorbs the heat from the air as it passes by, the air is cooled and is blown through the A/C vents as cold air. After the freon leaves the evaporator, it is returned to the compressor, where the process is started over again.