How Does a Car Air Conditioning System Work?

An automotive air conditioning system works a lot like the AC system that you have at home or the office....

An automotive air conditioning system works a lot like the AC system that you have at home or the office. It serves one very fundamental purpose, as well, and that is to cool you down. As a matter of fact, it would be quite difficult to imagine a modern vehicle without some means of providing a cooler and more comfortable ride especially when the scorching sun of summer unleashes its wrath. There are some folks who think that an air conditioning system in a car creates cold air. This is not true. Like other types of air conditioning systems, the AC in your car cools the air that is already in the car. It doesn’t produce it. How does it do this? Well, read on.

Woman turns on air conditioning

Components of a Car Air Conditioning System

It is best to get familiarized with the different components of the vehicle passenger cooling system to better understand the process of air conditioning. This will also pave the way for providing you with the answer to the question, how does a car AC work?

  • Compressor

Many consider the compressor as the heart of the air conditioning system of the car. As the name suggests, it “compresses” the refrigerant so that it turns from a gaseous state into a liquid state. The compressor connects to the crankshaft via a drive belt. As such, it draws its power from the engine. Whenever you turn on the car AC system, the compressor pumps gaseous or vaporized refrigerant to the condenser.

  • Condenser

In elementary science, we learned that condensation results from the rapid cooling of hot or warm air. The water vapor or moisture in hot air condenses to form a liquid state. This is what the condenser does. It is one of the most recognizable parts of the modern automotive AC system because it is very easy to check. This looks a lot like the radiator. It is also positioned right in front of the radiator. As such, if you are wondering why you have two “radiators”, the one in front is the condenser. This device turns or “condenses” the high-pressure, high-temperature, vaporized refrigerant coming from the compressor. The air that flows through the condenser removes the heat in the high-pressure refrigerant, cooling it down.

  • Evaporator

Among all the components of the modern vehicle AC system, the evaporator is the only one that’s located inside the passenger compartment. The rest of the components are in the engine bay. The evaporator looks like a very small radiator with fins and tubes. Cold air from the receiver-drier moves through the evaporator core. As air from the cabin circulates through the ducts, it is blown past the evaporator core and the heat is released. What comes out of the AC vents is cold and dry air.

  • Receiver

This component prepares the refrigerant for entry into the evaporator. It serves as a reservoir for the refrigerant while also removing any moisture that may be present in the refrigerant. It is important that built-in desiccants remove moisture from the refrigerant. If not, ice crystals can form and lead to blockage and mechanical damage.

  • Expansion Valve

The thermal expansion valve is the boundary between the high-pressure side of the system (including the compressor, condenser, and receiver) and the low-pressure side of the system. As the name implies, the expansion valve allows the expansion of the high-pressure liquid refrigerant coming from the receiver-drier. Because of the expansion, there is a reduction in pressure.

  • Refrigerant

While not a “component” of an automotive air conditioning system, the refrigerant is the lifeline of the system. Without it, heat will not be able to move out from the system and bring cooling comfort to everyone in the passenger compartment. At low pressures and temperatures, the refrigerant takes on a gaseous form. At high temperatures and pressures, the refrigerant is liquid.

AC vent

The Process of Cooling the Air in an AC System

Looking at the different parts of an automotive AC system, it should already be obvious how such technologies cool the air inside the cabin. We shall try to illustrate here the sequential steps on how such a system works.

  • The compressor compresses or pressurizes the refrigerant, turning it into a liquid form from its gaseous state.
  • The pressurized liquid refrigerant circulates through the series of tubes located in the condenser. This allows fresh air coming from the outside of the vehicle to come in contact with the liquid refrigerant. Because the condenser contains a higher-temperature liquid, there is a temperature gradient between the liquid and the fresh air. What happens is that heat moves from the liquid and into the air.
  • The refrigerant moves into the accumulator or receiver drier. A desiccant removes moisture that may be present in the refrigerant. This leads to the creation of a cooler refrigerant while also maintaining the integrity of the system
  • The cool refrigerant liquid flows into the orifice tube or expansion valve. It reduces fluid pressure, allowing it to move to the evaporator a lot easier.
  • The low-pressure liquid refrigerant moves through the evaporator. The air coming from the passenger compartment gets drawn into the evaporator and blasted through the evaporator core. Because the refrigerant is cooler, heat moves from the air and into the refrigerant. What happens now is that the air exiting the evaporator is cold air. Fans help blow the cold air through the vents and allow the cooling of the cabin. The process also reduces moisture in the evaporator’s air-side. This allows for the creation of drier air in the passenger cabin. At the same time, the system collects and drains the condensate. Because the liquid refrigerant in the system is now “hotter”, it turns into its gaseous state again.
  • The now-hot, low-pressure gaseous refrigerant circulates back to the compressor, ready to begin a new cycle.

Car air conditioners work to make our rides more comfortable and our journeys a lot more worthwhile. So, if someone asks, ‘how does a car AC work?’, you already know how to explain it.      


  1. How Does a Car Air Conditioning System Work? – Your Mechanic
  2. How Automotive Air Conditioning Works – HowStuffWorks