Automobile air conditioning (also called A/C) systems use air conditioning to cool the air in a vehicle.
In the refrigeration cycle, heat is transported from the passenger compartment to the environment. A refrigerator is an example of such a system, as it transports the heat out of the interior and into the ambient environment.
Circulating refrigerant gas vapor (which also carries the compressor lubricant oil across the system along with it) from the evaporator enters the gas compressor in the engine bay, usually an axial piston pump compressor, and is compressed to a higher pressure, resulting in a higher temperature as well. The hot, compressed refrigerant vapor is now at a temperature and pressure at which it can be condensed and is routed through a condenser, usually in front of the car's radiator. Here the refrigerant is cooled by air flowing across the condenser coils (originating from the vehicle's movement or from a fan, often the same fan of the cooling radiator if the condenser is mounted on it, automatically turned on when the vehicle is stationary or moving at low speeds) and condensed into a liquid. Thus, the circulating refrigerant rejects heat from the system and the heat is carried away by the air.
The condensed and pressurized liquid refrigerant is next routed through the receiver-drier, that is, a one way desiccant and filter cartridge that both dehydrates the refrigerant and compressor lubricant oil mixture in order to remove any residual water content (which would become ice inside the expansion valve and therefore clog it) that the vacuum done prior to the charging process didn't manage to remove from the system, and filters it in order to remove any solid particles carried by the mixture, and then through a thermal expansion valve where it undergoes an abrupt reduction in pressure. That pressure reduction results in flash evaporation of a part of the liquid refrigerant, lowering its temperature. The cold refrigerant is then routed through the evaporator coil in the passenger compartment.
The air, often after being filtered by a cabin air filter, is blowed by an adjustable speed electric powered centrifugal fan across the evaporator, causing the liquid part of the cold refrigerant mixture to evaporate as well, further lowering the temperature. The warm air is therefore cooled, and also deprived of any humidity (which condenses on the evaporator coils and is drained outside of the vehicle) in the process. It is then passed through an heater matrix, inside of which the engine's coolant circulates, where it can be reheated to a certain degree or even a certain temperature selected by the user and then delivered inside the vehicle's cabin through a set of adjustable vents. Another way of adjusting the desired air temperature, this time by working on the system's cooling capacity, is precisely regulating the centrifugal fan speed so that only the strictly required volumetric flow rate of air is cooled by the evaporator. The user is also given the option to close the vehicle's external air flaps, in order to achieve even faster and stronger cooling by recirculating the already cooled air inside the cabin to the evaporator.
To complete the refrigeration cycle, the refrigerant vapor is routed back into the compressor.
The warmer is the air that reaches the evaporator, the higher is the pressure of the vapor mixture discharged from it and therefore the higher is the load placed on the compressor and therefore on the engine to keep the refrigerant flowing through the system.
The compressor can be driven by the car's engine (e.g. via a belt, often the serpentine belt, and an electromagnetically actuated clutch; an electronically actuated variable displacement compressor can also be always directly driven by a belt without the need of any clutch and magnet at all) or by an electric motor.