How do car air conditioners cool and warm?

Automobile air conditioning and refrigeration system includes air conditioning compressor, condenser, liquid storage tank (now cars are basically integrated with condenser), evaporator, air conditioning pipeline, expansion valve, etc. With the development of automotive air conditioning technology, now the evaporator and expansion valve are basically integrated in the air conditioning HVAC. In addition to these two, HVAC also integrates blowers, heating devices and various sensors and actuators of the air conditioning system.
The work of the modulation cooling system is the process of continuous gasification and liquefaction of refrigerant. Taking the center of the compressor and expansion valve as the boundary, the whole refrigeration cycle can be divided into high and low pressure parts. The details can be understood from the above figure. The circulation process of refrigerant in the system can be divided into four working processes, as follows:
1. Compression. The low-temperature and low-pressure refrigerant gas treated by the evaporator is sucked into the compressor and compressed into high-temperature and high-pressure gas, and then input to the condenser.
2. Condensation and heat release. The refrigerant gas with high temperature and high pressure enters the condenser. Due to the decrease of pressure and temperature, the refrigerant gas condenses into liquid and releases a lot of heat to the outside atmosphere.
3. Throttle. After the refrigerant liquid with high temperature and pressure passes through the expansion device, the volume becomes larger, the pressure and temperature drop sharply, and it is discharged from the expansion valve in the form of mist (small droplets). This is the boundary between high and low pressure of refrigerant. The expansion valve has the function of throttling.
4. Evaporation. The mist refrigerant liquid enters the evaporator. Because the boiling point of the refrigerant is much lower than the temperature in the evaporator, the refrigerant liquid evaporates into gas. In the evaporation process, a large amount of surrounding heat is absorbed, and then the refrigerant vapor with low temperature and low pressure enters the compressor again.
If the above process is carried out repeatedly, the purpose of reducing the air temperature around the evaporator can be achieved. At the same time, the blower draws the cold air into the vehicle and exhausts the hot air in the vehicle, so as to reduce the temperature in the vehicle and achieve the refrigeration effect.

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