Air conditioners: How do they work?

An air conditioner cleans, circulates, cools and dehumidifies (removes undesirable moisture from) indoor air. A filter cleans the air by trapping dust and other small particles. An air handler (blower built into the system) circulates it, while the cooling and dehumidifying are accomplished by a process called refrigeration.

Refrigeration. Refrigeration cools a home by transferring heat inside a home to the outdoors. All central air conditioners employ two main units in this process – the indoor unit and the condensing unit.

The indoor unit. This unit removes undesirable indoor warmth and humidity. It includes the filter, the air handler and the evaporator coil. The air handler blows filtered air through the evaporator coil.

The evaporator coil is kept cold by the circulation of a substance called a refrigerant. Air that travels across the evaporator coil gives up heat (the colder coil absorbs it) and humidity (moisture condenses upon contact with the cold surface of the coil).

The cooler, drier air that continues through the air ducts is vented throughout your home to maintain your desired comfort level. Depending on the structure of your home, the ductwork may be above the ceiling or below the floor.

The condensing unit. Outdoors, at the condensing unit, an air conditioner releases the heat that was captured indoors. The same refrigerant that absorbed the heat indoors at low pressure is now pressurized – by the compressor – and is circulated through another coil, the condensing coil.

In the condensing coil, under high pressure, the refrigerant releases its heat very quickly, making the coil itself hot. A fan blows across the coil, cooling its temperature down and transferring the heat to the outside air.