The air conditioner in your car works in almost the same way that the one in your home does. The difference is only in the controls—only very new or luxury vehicles have a thermostat with a temperature-like home system. Even if your car does have this feature, the system works the same way to make the car cool. The control panel is just a little fancier.
An air conditioner works by compressing a chemical refrigerant to force it to go from a gas to a liquid. When the refrigerant changes state, from a liquid into gas, heat is transferred. Air that is bound for the cabin will pass over the evaporator. In effect, the heat is taken out of the air and put into the refrigerant. You can’t actually “create” cold air, so instead, you move the heat from your cabin air into the refrigerant. The now-hot refrigerant is trapped in a closed circuit, and it gets taken outside to where the compressor again compresses the gas back into a liquid, and the cycle starts again. At this point, the refrigerant creates heat, but it’s outside the cabin of the car.
It’s the temperature of the evaporator that makes the air cold, not the compressor itself. As long as the evaporator gets cold and has air flowing over it, the cabin will cool down.
There are three other important parts of your car’s air conditioning system you should understand. The first is the fan, which blows air over the evaporator and through the ducts. It’s not connected to the compressor, so the fan can blow outside air, the air warmed by the heater, or air-cooled by the evaporator.
The second control to understand is the recirculate button. This pulls air only from the inside of the car. It’s an important part of the system because the air conditioner can only cool down a given volume of air so much. If the air it’s trying to cool is continuously coming from the outside, it will never get very far. The recirculate button allows it to use the air it’s already started to cool down from inside the car’s cabin. It will get cooler and cooler the more times it’s recirculated.
And finally, there is the mixture control, which mixes hot or cold air. You can use it to adjust the airflow between the heater and the air conditioner. If the air conditioner air is too cold, you can mellow it out a bit.
So, to get maximum air conditioning in your car, you need the fan on full, the recirculate button on, the mixture control to cold, and the air conditioner compressor on.
The air conditioner compressor, which usually has its button on the panel, will cycle on and off as necessary to produce the maximum amount of hot air. Like any other piece of equipment in your car, it has a duty cycle and temperature limits that it is designed to not exceed.
The system cannot allow the cooling coils to freeze up, and it cannot allow the compressor to overheat. To accomplish this, the compressor will cycle on and off at regular intervals. So long as cold air is blowing out of the vents, there is nothing to worry about. If it’s cycling rapidly or doesn’t blow any cold air at all, it’s time to see your mechanic for a check-up.