Whew! It's easy to tell when summer is upon us. The mercury in the thermometer heads upward as the Sun beats down, and sweat breaks out on our foreheads as we enjoy the warmer weather.

While many of us look forward to summer, we don't like to sweat all day long. After some time in the sunshine, most of us look forward to a tall glass of icy lemonade as we relax in those machine-generated drafts of cold air. What are we talking about? Air conditioning, of course!

Modern life wouldn't be as comfortable as it is without air conditioning technology. The Energy Information Administration estimates that approximately 87 percent of all homes in the United States use some form of air conditioning. But exactly how does air conditioning work?

Do fans inside air-conditioning units blow air across magic polar ice crystals to create the cool breezes we enjoy? Not quite! The secret of the air conditioner is putting what we know about science to work for us.

Air conditioners come in many shapes and sizes, but they all work in much the same way. Rather than putting cold air into the house, air conditioners take heat out of a house. They use chemicals, called refrigerants, which can switch back and forth from a liquid to a gas quickly and easily.

Refrigerants soak up heat inside the house and carry it outside, cooling the house in a repeating cycle. The two most common refrigerants used today are R-22 and R-410A. Chemically, these refrigerants are known as hydrochlorofluorocarbons or HCFCs.

The three basic parts of an air conditioner are the evaporator, the compressor, and the condenser. The evaporator can be found on the part of the air conditioner inside the house, while the compressor and condenser are located in the outside unit.

Inside the house, fans move air across the evaporator. Usually, an air intake near the ceiling sucks in warm air and pushes it past the evaporator coils. Cold, liquid refrigerant in the coils absorbs heat from the air. The cooled air is then blown by fans through air ducts to the rest of the house.

As this happens, the liquid refrigerant heats up and changes to a gas. The vaporized refrigerant moves outside to the compressor, which compresses the gas to an even higher temperature and pressure.

The pressurized vapor then passes over the condenser. As the heat radiates away, the vaporized refrigerant condenses back into a liquid. Most air conditioner condensers feature thin metal fins packed tightly together. These fins help to dissipate the heat quickly and efficiently.

The cooled liquid refrigerant is then cycled back inside the house to the evaporator. The process starts all over again. This cycle repeats until the air temperature inside the house reaches the desired temperature, which is usually set by the homeowner by selecting a particular temperature on the thermostat connected to the air conditioner.