You’re stopped in traffic on an August afternoon. Sweat drips down your neck all the way down your back until your shirt absorbs it making a damp spot between you and the seat. Your legs are either stuck to the vinyl or prickled by its cheap velvet. Your hands feel like they’re about to slip off the steering wheel, and your thankful your eyebrows are keeping the sweat from running into your eyes. Well mostly.

What’s missing from this picture? A functioning automotive air conditioner. It has become almost standard with 99% of all new cars as of the summer of 2010 coming equipped with AC. When it’s missing we notice.

Auto Air Conditioning Isn’t Something New

Air conditioning has worked pretty much the same way for its entire existence, it cools and removes humidity from the air. But Auto air conditioning has been with us longer than you might think. Packard invented automotive AC back in 1939, and in 1940 was the first car company to offer factory installed air conditioning. Of course this early system didn’t have a thermostat but it was better than not having AC at all. The idea caught on and by 1969 more than half of all new cars sold had factory installed AC.

Eventually, it was determined that the refrigerant used for decades in automotive AC , known as R12 was damaging the ozone and it was banned from manufacture in the United States and an alternative, R-134a took its place in all cars after 1996.

There are three main parts to the system- the compressor, condenser and the evaporator. Let’s take a look at each.

The Compressor

The compressor is a pump driven by a belt attached to the engine’s crank shaft. When the refrigerant is drawn into the compressor it is in a low pressure gaseous state. Once the gas is inside the pump, the compressor lives up to its name. The belt drives the pump, which puts the gas under pressure and forces it out to the condenser. Compressors cannot compress liquids, only gases.

The Condenser

The condenser is basically a radiator and serves the same purpose as the one that cools your engine, to radiate heat out of the system. The refrigerant enters the condenser as a pressurized gas from the compressor. The process of pressurizing the gas and moving it to the condenser creates heat, but air flowing around the twisting tubes of the condenser cool the refrigerant down until it forms a liquid again. Imagine steam cooling down and condensing back into water and you have the idea. The liquid refrigerant is now high pressure liquid and nearly ready to cool the car.

The Evaporator

The evaporator, this is where the magic happens. While all the other parts of the system are located under the hood, this one is in the cabin under the dash. It also looks like a radiator with tubes and fins but its job is to absorb heat rather than t o dissipate it. Refrigerant enters the evaporator as a cold, low pressure liquid. At this point it has a very low boiling point and the heat in the cabin makes the refrigerant boil and become a gas again. In its gaseous form refrigerant can absorb a lot of heat. The gas moves out of the evaporator and out of the cabin taking the heat with it.