How Does a Car’s Air Conditioning Work?

As you sit in traffic, your car idling in the summer heat, the air conditioning keeps you cool and comfortable. Though you are sitting in a car going nowhere, your car’s air conditioning is working hard – and here’s how.

It’s Simple! Thermodynamics!

Air conditioning is simple, really. It operates on four principles of thermodynamics: evaporation, condensation, compression, and expansion.

Button for car's air conditioning.

A lot happens with the push of a button.

  1. Evaporation
    When liquid on a surface, such as your skin, comes into contact with air, it seeks an equilibrium, so it begins to evaporate. As it evaporates, it removes heat from your skin, which causes your skin to feel cool. The process of evaporation in the air conditioning of your car is what makes it possible to create cool air that is pumped into the passenger compartment at the push of a button, push of a lever, or turn of dial – or all three, depending on the make, model, and age of your car.
  2. Condensation
    If you wear glasses, or sunglasses, you’ve noticed that when you walk into a warm room from the cold, your glasses steam up. That’s condensation. The air of the warm room can hold more moisture than the cold air around your glasses, so as the air around your glasses cools – as the warm air makes contact with the cold surface of your glasses – it condenses. The air has less capacity to hold moisture, so it condenses into water on your glasses.
  3. Compression
    At some point all gases eventually become liquid. An example of that would be a can of air freshener – it’s liquid inside the can, but is a gas when you spray it. The pressure inside the can is higher than outside the can (hence, strong, steel cans), so the propellant inside is liquid. The pressure “presses” the gas into a liquid state. When it is released, it seeks equilibrium with the air and turns to vapor.
  4. Expansion
    When you spray the air freshener, you’ll notice how cold it feels. That is because the propellant, or gas, has expanded in volume very quickly. As the gas moves, it loses energy, or heat, and cools rapidly. You’ll also notice that if you spray for a few seconds, the can becomes cold, too.

How Your Car’s A/C System Applies those Principles

Enough with the science lessons. The air conditioning system in your car has a few important parts and processes that operate on the aforementioned principles. It’s a very busy system, indeed.

  1. Compressor
    The compressor is the work horse of the air conditioning system, powered by a drive belt connected to the crankshaft of the engine. When the A/C is on, the compressor pumps refrigerant vapor under high pressure to the condenser.
  2. Condenser
    The condenser changes the high-pressure refrigerant vapor to a liquid. It is mounted in front of the engine’s radiator. The vapor is condensed to a liquid because of the high pressure that is pushing it in. This generates a lot of heat. The heat is then removed from the condenser by air flowing rapidly through the condenser on the outside.
  3. Receiver
    The receiver-dryer removes moisture from the refrigerant. The refrigerant, which is now liquid, moves to the receiver-dryer. This is a container for the liquid refrigerant and removes any moisture that may have leaked into the refrigerant. Moisture in the system can cause ice crystals, which in turn cause blockages and mechanical damage.
  4. Expansion Valve
    The pressurized refrigerant flows from the receiver-drier to the expansion valve. The valve removes pressure from the liquid refrigerant so it can expand and become refrigerant vapor in the evaporator.
  5. Evaporator
    As the cold low-pressure refrigerant is passed into the evaporator, it vaporizes and absorbs heat from the air in the passenger compartment. The evaporator has fins and tubes that turn cool in this process, and as the blower fan inside the passenger compartment pushes air over the outside of the evaporator, cold air is circulated inside the car.

In a nutshell:

  1. Compressor pumps refrigerant vapor.
  2. Condenser changes refrigerant vapor to liquid.
  3. Receiver-dryer removes moisture from the refrigerant.
  4. Expansion valve removes pressure from the refrigerant so it can become vapor.
  5. Evaporator vaporizes & absorbs heat from the air in the passenger compartment.
  6. Blower fan pushes air over the outside of the evaporator.
  7. Cold air is circulated inside the passenger compartment!

Another benefit of air conditioning can be gotten in wintertime. It not only cools, but it can be run in conjunction with the heating system to dehumidify, or defog, your car and the insides of the windows.

All air conditioners work the same way whether they are installed in a building, or in a car. They are systems that work on basic scientific principles, but are run constantly to keep our environments comfortable. That is why it’s important to have your car’s air conditioning system checked regularly to make sure it’s running efficiently.

For normal, everyday car maintenance and repairs, such as air conditioning, oil changes, brake inspection and service, shocks and struts, mufflers, and tune ups, AAMCO can help. Schedule an appointment today at your local AAMCO Colorado shop.