The automotive air conditioning refrigeration system consists of a compressor, condenser, receiver drier, expansion valve, evaporator, blower motor and other components. All parts are connected by copper (or aluminum) tubes and high-pressure rubber hoses to form a closed system. When the refrigeration system operates, refrigerant circulates in this closed system in different states, with four basic processes in each cycle:    
1. Compression process: The compressor draws in low-temperature, low-pressure refrigerant vapor from the evaporator outlet, compresses it into high-temperature, high-pressure gas, and discharges it.    
2. Heat rejection process: The high-temperature, high-pressure superheated refrigerant gas enters the condenser. As pressure and temperature drop, the refrigerant gas condenses into liquid and releases a large amount of heat.  
3. Throttling process: The relatively high-temperature and high-pressure liquid refrigerant passes through the expansion device, where its volume expands and pressure and temperature drop sharply, exiting as a fine mist (tiny liquid droplets).
4. Heat absorption process: The misted liquid refrigerant enters the evaporator. Since the boiling point of the refrigerant is much lower than the temperature inside the evaporator, the liquid vaporizes into gas. During vaporization, it absorbs a large amount of surrounding heat, and the low-temperature, low-pressure refrigerant vapor then re-enters the compressor.
The above processes repeat continuously to lower the air temperature around the evaporator.

Functions of automatic air conditioning include automatic adjustment of in-car temperature and humidity, automatic control of air return and supply modes, as well as regulation of operating modes and ventilation volume. The electronic control unit (ECU) operates the AC system automatically based on settings entered by the driver or passengers via buttons on the AC control panel. It also adjusts supply air temperature and fan speed in real time according to input signals from various sensors, maintaining an optimal in-car air environment.