The refrigerant compressor sucks the low pressure (low temperature) refrigerant in the evaporator into the compressor cylinder. Refrigerant of high temperature high pressure steam pressure to the condenser, the condenser, higher temperature of the refrigerant vapor heat exchange with a relatively low temperature of the cooling water or air, the quantity of heat of refrigerant was taken away by water or air cooling down, refrigerant vapor into liquid. This part of liquid is then transported to the expansion valve, which is throttled by the expansion valve into a low-temperature and low-pressure liquid and enters the evaporator. In the evaporator, the cold and low pressure refrigerant liquid absorbs the heat of compressed air and vaporizes (commonly known as "evaporation"). After the compressed air is cooled, a large amount of liquid water is condensed out. The refrigerant vapor in the evaporator is sucked away by the compressor, so that the refrigerant is compressed, condensed, throttled and evaporated in the system, thus completing a cycle.