Air conditioners and refrigerators work the same way. Instead of cooling just the small, insulated space inside of a refrigerator, an air conditioner cools a whole car.



Air conditioners use chemicals that easily convert from a gas to a liquid and back again. This chemical is used to transfer heat from the air inside of a car to the outside air.



The machine has three main parts. They are a compressor, a condenser and an evaporator. The compressor is located on the engine, because it is typically belt driven. The condenser is located at the front of the car to take advantage of air coming in from the moving vehicle. The evaporator is located closer to the cabin of the car, usually under the dash or near the firewall.



The working fluid arrives at the compressor as a cool, low-pressure gas. The compressor squeezes the fluid. This packs the molecule of the fluid closer together. The closer the molecules are together, the high its energy and its temperature. The working fluid leaves the compressor as a hot, high pressure gas and flows into the condenser. If you look at the condenser, look for the part that has metal fins all around. The fins act just like the radiator in the car and helps the heat go away, or dissipate, more quickly.



When the working fluid leaves the condenser, its temperature is much cooler and it has changed from a gas to a liquid under high pressure. The liquid goes into the evaporator through a very tiny, narrow hole. On the other side, the liquid's pressure drops. When it does it begins to evaporate into a gas. As the liquid changes to gas and evaporates, it extracts heat from the air around it. The heat in the air is needed to separate the molecules of the fluid from a liquid to a gas.



The evaporator also has metal fins to help in exchange the thermal energy with the surrounding air. By the time the working fluid leaves the evaporator, it is a cool, low pressure gas. It then returns to the compressor to begin its trip all over again. Connected to the evaporator is a fan that circulates the air inside the car to blow across the evaporator fins.



Hot air is lighter than cold air, so the hot air in the car rises to the top of the interior just like it rises to the top of a room. There is a vent there where air is sucked into the air conditioner and goes down ducts. The hot air is used to cool the gas in the evaporator. As the heat is removed from the air, the air is cooled. It is then blown into the car through other ducts usually at the floor level.



This continues over and over and over until the interior of the car reaches the temperature you want the car cooled to. The thermostat senses that the temperature has reached the right setting and turns off the air conditioner. As the room warms up, the thermostat turns the air conditioner back on until the car reaches the temperature