Air conditioners employ the same operating principles and basic components as refrigerators. Refrigerators use energy (usually electricity) to transfer heat from the cool interior of the refrigerator to the relatively warm surroundings; likewise, an air conditioner uses energy to transfer heat from the interior space to the relatively warm outside environment.

An air conditioner uses a cold indoor coil called the evaporator. The condenser, a hot outdoor coil, releases the collected heat outside. The evaporator and condenser coils are serpentine tubing surrounded by aluminum fins. This tubing is usually made of copper.

A pump, called the compressor, moves a heat transfer fluid (or refrigerant) between the evaporator and the condenser. The pump forces the refrigerant through the circuit of tubing and fins in the coils.

The liquid refrigerant evaporates in the indoor evaporator coil, pulling heat out of indoor air and thereby cooling your home. The hot refrigerant gas is pumped outdoors into the condenser where it reverts back to a liquid, giving up its heat to the outside air flowing over the condenser's metal tubing and fins.


The two most common types of air conditioners are room air conditioners and central air conditioners. A compromise between the two types of systems is provided by ductless, mini-split air conditioners.

Room air conditioners cool just one room or small space, rather than an entire building.

Central air conditioners circulate cool air through a system of supply and return ducts that carry cool air from the air conditioner to the building. This cooled air becomes warmer as it circulates through the building; then it flows back to the central air conditioner through return ducts and registers.

Ductless, mini-split systems are similar to central air conditioners in that they have an outdoor compressor or condenser and an indoor air-handling unit. However, because they are "ductless," they are often used in buildings with non-ducted systems. Instead, a conduit with the power cable, refrigerant tubing, suction tubing, and condensate drain links the outdoor and indoor units.