The air conditioning in almost all cars follow the same relatively simple system. Since the design is almost universal, a basic familiarity with how it works can greatly facilitate a car owner’s ability to diagnose problems with their air conditioning system, or assess one when considering buying a used car.
A car’s air conditioning system contains a refrigerant that’s normally gaseous under room temperature conditions, but is held under pressure in the system. The changeability of the refrigerant is what makes it useful in climate control. When a car’s A/C is turned on it’s compressed, causing it to transition from a gas to a liquid as the molecules are forced together. Compression, activated by pressure switches brings its temperature down, just as lowering a substances temperature directly would compress it. A condenser in front of a car’s radiator compresses it when the pressure switches are tripped by a signal from the car’s dashboard, and then it’s released from the condenser through an expansion valve, which acts as a very small opening.
The sudden pressure change that results inside the evaporator makes it cold, and then air is passed through it by a blower and into the car interior. The gas is then recovered inside the evaporator and returned to where it’s stored in the system. This all occurs in a closed system the refrigerant is continuously recycled through. A filter drier filters it and removes moisture, and it moves between components via hoses. The actions of the filter drier keep the A/C mechanism from being damaged by rust or the hoses no longer allowing airflow.
The compressor is powered by the engine, using the system of the serpentine belt. It basically runs on energy that’s already moving through the car as a result of it running. The compressor is connected to the evaporator. Inside the car, the status of the A/C is represented on a pair of manifold gauges. Manifold gauges display the pressure in parts of the system, allowing maintenance and diagnosis. Some systems have orifice tubes instead of an expansion valve, the difference being that the tube is a fixed size, but an expansion valve can vary as a result of differences in temperature.
The setting available to the driver control things like blower fan speed, and how much cold air is mixed in with the rest of the air passed through the system. Commands from the computer controlled by the driver cause the compressor to start pressurization.