Ever wonder how an air conditioner works?

When the household thermostat signals the air conditioning system to lower room air temperature, a whole sequence of events begins.

The air handling unit kicks on, drawing room air in from various parts of the house through return-air ducts. This air is pulled through a filter where airborne particles such as dust and lint are removed-in fact, sophisticated filters may remove microscopic pollutants as well, then it's routed to air supply ductwork that carries it back to rooms. Whenever an air conditioner is running, this cycle repeats continually. But how does that evaporator coil get cold in the first place? That happens through the magic of refrigeration. Every air conditioner has three main parts: a condenser, an evaporator and a compressor. With a typical split system the condenser and compressor are located in an outdoor unit; the evaporator is mounted in the air handling unit (which is often a forced air furnace). (With a package system, all components are located in a single outdoor unit that may be located on the ground or roof. A refrigerant circulates through copper tubing that runs between these components. This refrigerant receives and releases heat as it raises and lowers in temperature, changing from liquid to gas and back to liquid. The refrigerant is especially cold when it begins to circulate through the indoor coil. As the air handler pushes warm room air across this coil, the cold refrigerant absorbs so much heat from the air that it turns into a vapor. As a vapor, it travels to a compressor that pressurizes it and it moves through the outdoor coil, which jettisons the heat. A fan helps to dissipate this heat. The refrigerant then passes through an expansion device which converts it to a low-pressure, low-temperature liquid, which returns to the indoor coil. And so the cycle continues.