While it is true that air-conditioning makes your home cooler, it really makes your house less warm by transferring the heat out of doors. It has coils with fins similar to those in an automobile radiator. A compressor sends refrigerant through the coils, and the air is cooled as it is forced over the coils. Many people buy air conditioners that are too large, in the false belief that an oversized unit will cool better. Those units are less effective and waste energy at the same time.
Air conditioners remove both heat and moisture from the air.
Moisture is removed when the warm air passes over the coils. If the unit is too large, it will cool the room quickly, but remove less of the moisture, leaving the room with a damp, clammy feeling. To determine what size you need, the U.S. Department of Energy suggests multiplying the square footage of the space to be cooled by 20. If the room is heavily shaded, reduce capacity by 10 percent. If the room is very sunny, increase capacity by 10 percent.