Central Air Conditioner
Air conditioners are powered by electricity, and a lot of energy is needed to run them. They also use a refrigerant to transfer heat from indoors to outdoors. This refrigerant circulates through a closed-circuit loop of copper tubing that runs between an outdoor coil, called a condenser, and an indoor coil, called an evaporator. The refrigerant raises and drops in temperature as it absorbs and gives off heat, and it changes from liquid to gas and back to liquid again as its temperature and pressure change.
When cold refrigerant circulates through the indoor evaporator, it absorbs the heat from the room air blown across it. As the refrigerant absorbs the heat, it vaporizes and travels through the tubing to the condenser coil and compressor unit that are outdoors. As it moves through the unit, it emits heat that dissipates into the outdoor air; an electric fan that blows across the coil assists the process. As a result, the refrigerant cools and becomes a high-pressure liquid. An expansion valve further reduces the temperature and pressure, then returns the refrigerant to the evaporator, completing the cycle.
A central air conditioner usually is combined with a forced-air furnace, using the furnace's blower to draw room air into the unit through the return-air ductwork that runs throughout the house.
A room air conditioner, mounted in a window or built into an exterior wall, contains a condenser coil, a compressor, an evaporator coil, and a blower, just like its larger cousin, the central air conditioner.
Hybrids split ductless systems cool different zones of a house, each controlled separately. A split-system's main components are separated: an evaporator coil is indoors with the furnace, and a condenser coil and compressor unit are outdoors.
-- Tips courtesy of HomeAdvisor.com