How Car Air Conditioning Works

Have you ever wondered how car air conditioning works? Well the car air conditioner has pretty much worked the same way for its entire existence in the modern world and that is, it cools and removes humidity from the air. 

When it comes to Car Air Conditioning, there are three main parts to the system.

  1. Compressor
  2. Condenser 
  3. Evaporator

There are also a few other intricate parts to keep the system running smoothly such as the receiver and thermal expansion valve.

In this article, we will explain how each of these specific parts works to give you an understanding how car conditioning works to produce cool air when driving.

The High-pressure Side

All car air conditioning systems are fully closed loops. In one full loop it changes the state of matter 3 times with a  high-pressure side and low-pressure side.

We’ll start with the high-pressure side as it leads from the engine to the passenger compartment.

Car AC Compressor

The compressor is a pump driven by a belt attached to the engine’s crankshaft. The refrigerant is drawn into the compressor as a low-pressure gaseous form.

Once the gas is in the pump it is put under extreme pressure (250psi-400psi) and is forced out to the condenser. Compressors cannot compress liquids, only gasses. 

Car AC Condenser

The condenser is basically a radiator, and it serves a similar purpose to the one in your vehicle, to draw heat out of the system. The refrigerant enters the condenser as a high pressure gas from the compressor. 

The process of pressurizing the gas and moving it to the condenser creates heat, but air flowing through the fins and tubes of the condenser cools the refrigerant down (condenses) changing the state of the gas to a high pressure liquid. 

Imagine steam cooling down and condensing back into water, and you’ve got the idea. The liquid refrigerant is now a high-pressure liquid and nearly ready to cool the car.


The refrigerant needs to be prepped for the evaporator. As it moves out of the condenser, the liquid goes through a little reservoir installed in the line. This receiver-drier  contains desiccants, small granules that attract moisture.

In the receiver-dryer, the desiccants remove any water that has entered the system. If the moisture is allowed to remain in the system this will react with the internal metal surfaces and  mixing with the system lubrication oil creating acids and sludge build up causing premature failure to the air- conditioning system.

How Car Air Conditioning Works Diagram
Car Air Conditioning System Diagram

The Low-pressure Side

Now that we’ve finished with the high-pressure side, let’s now take a look at the low-pressure side of the car air conditioning system.

Thermal Expansion Valve 

Here, the system changes from the high-pressure side to the low-pressure side. If you were to touch this part of the system, you’d feel it change from hot to cold.

The high-pressure liquid refrigerant flows from the receiver-dryer through the expansion valve, where it is allowed to expand. This expansion reduces the pressure on the refrigerant, so it can move into the evaporator.

The valve senses pressure and regulates the flow of refrigerant, which allows the system to operate steadily, but the moving parts of the valve can wear out and sometimes require replacement.

Car AC Evaporator

While all the other parts of the system are located in the engine compartment, the evaporator is in the cabin, usually above the footwell on the passenger side. The evaporator looks similar to a radiator, with its coil of tubes and fins, but its job is to absorb heat rather than dissipate it.

Refrigerant enters the evaporator coil as a cold, low-pressure liquid, ideally at 0 degrees Celsius, which is why you don’t want any water in the system. The refrigerant doesn’t freeze at this temperature, but it does have a very low boiling point. 

The gas moves out of the evaporator and out of the passenger compartment of the car, taking the heat with it. A fan blowing over the outside of the evaporator coil blows cool air into the passenger compartment. The refrigerant in gas form then enters the compressor, where it is pressurized and the whole process starts all over again.

How Car Air Conditioning Works Video

Perhaps you’re more of a visual person so watch the video below on “How car air conditioning works”.

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