Automotive air conditioning is the same as our familiar home air conditioning refrigeration principle. They are all cooled by the principle that R12 and R134a is compressed and released, and the volume is rapidly expanded to absorb a large amount of heat. (Because of the destruction of the atmospheric ozone layer by R12, developed countries have switched to R134a as a refrigerant since 1996.) The structure of automotive air conditioners is similar to that of household split air conditioners. Its compressors are often installed on engines. It is driven by a belt (also directly driven). The condenser is installed in front of the radiator of the car, and the evaporator is inside the car. The low-pressure gaseous refrigerant from the evaporator flows through the compressor to become high-temperature and high-pressure gas. The condenser heat pipe is cooled and cooled to become a high-pressure and low-temperature liquid, and then dehumidified and buffered by a liquid storage dryer, and then flows to the expansion valve at a relatively stable pressure and flow rate, and then flows to the evaporator through throttling and pressure reduction. When the refrigerant is in a low pressure environment, it evaporates and absorbs a large amount of heat. The air in the cabin continues to flow through the evaporator, and the temperature inside the cabin is thus reduced. The liquid refrigerant flows through the evaporator and becomes a low-pressure gas again, and is again sucked into the compressor for the next cycle. In the whole system, the expansion valve is the mechanism for controlling the refrigerant to enter the evaporator. When the refrigerant enters the evaporator too much, it is not easy to evaporate and too little cold air is insufficient, so the expansion valve is the adjustment center. The compressor is the heart of the system, the source of power for the system cycle.