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How a Central Air Conditioner Works
central air conditioner unitWhen the household thermostat signals the air conditioning system to lower 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 the rooms. Whenever an air conditioner is running, this cycle repeats continually.

But how does the 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 the 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 of the components are located in a single outdoor unit that may be located on the ground or on the roof of the house.)

A refrigerant such as freon 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 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 moves it through the outdoor coil, which jettisons the heat.

A fan also helps to dissipate this heat. The refrigerant then passes through an expansion device that converts it to a low-pressure, low-temperature liquid, which returns to the indoor coil. And so the cycle continues.
how central air conditioner conditioning works diagram
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Lennox.
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