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How Air Conditioning Works

Learn the ins-and-outs of how air conditioning works - from who invented it (Willis Carrier) to basic principles and how A/C works.

Outdoor AC Unit

Summer heat can be brutal, and during the dog days of the season, air conditioning is a saving grace. We can thank an electrical engineer named Willis Haviland Carrier for this relief. He invented air conditioning in 1902 to remove humidity from the air at the Sackett-Wilhelms Lithographing and Publishing Company in Brooklyn.

Carrier’s first air conditioning system worked by moving air over chilled pipes. Cold air has less humidity, so as part of this process, moisture was removed from the air in the office building. As the humidity decreased, so did the temperature.

For many, air conditioning is a modern convenience we take for granted. How does an air conditioner work and how does it keep you comfortable when the temperatures rise? Read on to learn the ins and outs.

Basic principles – refrigerants

At the most basic level, air conditioners operate on the principle that liquids absorb heat as they convert to gases. Residential air conditioners use two common refrigerants to achieve this process on demand: R-22 and R-410A, both hydrochlorofluorocarbons.

R-22, also known as Freon, was the most common air conditioning refrigerant for decades. However, the Environmental Protection Agency (EPA) has identified it as a substance that depletes the ozone layer and has enacted a plan to completely phase out its use by 2020. It is being replaced by R-410A, a more environmentally friendly alternative.

Regardless of which refrigerant your unit currently uses, they both serve the same basic purpose: to absorb heat from the air within your home and convert from a liquid to a vapor, cooling the air.

Of course, that’s not the end of the story. Besides refrigerants, your AC unit has four key parts that each play an important role in maintaining a comfortable temperature inside your house.


This is where the refrigerant evaporates into a gas. Fans blow air from your home across evaporator coils containing the refrigerant. As this happens, the refrigerant absorbs the heat and makes the air from your home cooler. This process also removes moisture and humidity from the air. In a central AC unit, the evaporator is found inside your house.


Next, after the refrigerant has vaporized, it moves to the compressor. In central AC units, this is located outside of your home. The refrigerant needs to be returned to a liquid state for your unit to keep functioning properly. The first step in this process happens inside the compressor, where the pressure and temperature of the refrigerant gas are increased.


Following the compressor, the hot, pressurized gas moves on to the condenser for the third step in the process. From here, the refrigerant is cooled and becomes a liquid again and is returned to the home. This process produces additional heat, which the AC unit filters outside through condenser coils and a fan.

Expansion Device

The expansion device plays a basic, but important, role. It controls the flow of refrigerant into the evaporator.

While there are some variations depending on the type of unit in question (wall or central AC, for example), all air conditioners have the same basic parts and operate on the same basic system.

Regular maintenance matters

While the principles on which an air conditioner operates are relatively simple, an AC unit is still a piece of machinery that requires routine care and maintenance to avoid malfunctions. There are basic checks you can perform yourself, such as replacing your unit’s filter and making sure that your outdoor unit is sitting level, is free of debris, has at least two feet of space around it and has proper insulation around the refrigerant lines.

Still, there are times when it pays to have the professionals take a look at things. Of course, if you turn on your unit and hear a strange noise or you notice that your rooms are not cooling properly, it’s definitely time to call in an expert. You can elect to have air conditioning professionals check your unit annually, typically once in the spring and once in the fall, to ensure proper function and refrigerant levels.

Despite your best efforts to avoid it, there may be a time when your air conditioning acts up. Of course, this always seems to happen when temperatures soar. An American Home Shield® home warranty can help provide protection for unexpected issues and covered components of your air conditioner. Be sure you're prepared for the worst of the summer heat. Learn more about air conditioner coverage.

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