Automotive air conditioning refrigerating system consists of compressor, condenser, liquid dryer, expansion valve, evaporator and blower, etc.Between each components USES the copper or aluminum tube and high pressure rubber hose connection into a closed system.Refrigeration system, refrigerant in different state in circulating in the closed system, each cycle has four basic process: 1, the compression process: the exit of the low temperature low pressure refrigerant gas compressor suction evaporator, put it into high temperature and high pressure gas discharge of the compressor.2, the cooling process, superheated refrigerant of high temperature and high pressure gas entering the condenser, due to the pressure and temperature is reduced, condensed into liquid refrigerant gases, side by side a lot of heat.3, throttling process: high temperature and pressure of refrigerant liquid after expansion device volume become bigger, and the pressure and the temperature fell sharply, with mist exhaust expansion device (tiny droplets).4, endothermic process: fog refrigerant liquid into the evaporator, therefore when the refrigerant boiling point is far lower than the temperature in evaporator, thus evaporation refrigerant liquid to gas.Around a lot in the process of evaporation absorbs heat, then low temperature low pressure refrigerant vapor into the compressor.The cycle of the process, to achieve the purpose of reduce the ambient air temperature of the evaporator.