Almost everyone has an air conditioning system of some sort in their home and/or business. They all know that the purpose of the system is to cool the air inside the home or business to make it more comfortable during hot weather. However, not everyone knows just how an AC unit works.

The idea for air conditioning is based on the idea that heat must be applied to a liquid in order to convert it to a gas. This scientific principle is sound and holds true with virtually every substance known. Look at water, for example. This is a good example because we see water in all three states as a matter of our normal lives. If we remove enough heat from liquid water, it freezes to form to form ice. If we heat liquid water to 212 degrees Fahrenheit, it boils, changing from liquid to gas.

Air conditioners use a substance that is normally a gas at room temperature. This was once Freon, but another substance is now used because Freon was determined to be harmful to the ozone layer of the atmosphere. However, the principle remains the same.

This refrigerant gas is pumped into a compressor, usually located outside the home, at low pressure. It is compressed to a point where it must become a liquid because there are too many molecules in a confined space to maintain a gaseous state. From here, the liquid enters another part of the unit known as the condenser.

Condensation normally refers to a gas losing enough heat to convert back to a liquid. However, in the case of this refrigerant, the hot liquid enters the condenser, which looks very much like a radiator on a car, although the shape may differ somewhat. The liquid circulates through a long coil of tubing that has air flowing over it. The excess heat in the liquid is bled off to the air flowing over the condenser, cooling the liquid.

This high-pressure liquid is then pumped into an evaporator found inside the area to be cooled. The liquid enters a space where it has plenty of room to expand and form a gas again. This drops the pressure of the liquid, cooling it dramatically even as it evaporates into a gas. The low-pressure, low-temperature gas is circulated through another coil similar to the condenser. However, in this case, the cool gas inside the coil absorbs heat from the inside air flowing across it in order to maintain its gaseous state.

This heated gas is then returned at low pressure to the compressor in order to begin the cycle again. It is compressed to form a hot liquid, sent to a condenser where the excess heat is released to the outside air and brought back to the evaporator where heat is absorbed from the inside air.

Heat pumps are a special type of air conditioner that incorporates a switch that allows one to reverse this flow to create a heater. Therefore, in summer, heat is removed from the inside air and released to the outside. In winter, heat is absorbed from the outside air and released inside. These units are generally more energy efficient than older standard models.