The thermal expansion valve realizes the throttling from the condensing pressure to the evaporating pressure, and at the same time controls the flow of the refrigerant; although its volume is small, it has a huge effect. Its working quality directly determines the working quality of the entire system and gives it in the best way. The evaporator provides liquid to ensure the stable superheat of the refrigerant vapor at the outlet of the evaporator. The temperature sensing bulb must be in good contact with the suction pipe of the compressor to accurately sense the suction temperature of the compressor. It is usually filled with the inside of the refrigeration system The same refrigerant, so that the pressure feedback through the temperature sensor is the saturation pressure of the type of refrigerant corresponding to the compressor suction temperature, and the expansion valve ensures that when the operating environment changes (such as thermal load changes) , To achieve the best and best liquid supply mode of the evaporator.