Central air conditioner is a system that cools one or more rooms in a house or building. 

An air-conditioning system blows cooled air through duct to deliver it throughout the interior rooms. This differs from a portable room or window air conditioner, which is meant to cool only a single room.

Air conditioners use refrigeration principles to cool the air. To do this job, a condenser, compressor and evaporator work together.

Air conditioners may look alike, but check the SEER ratings (Seasonal Energy Efficiency Ratio).

A 13 SEER rated air conditioner uses 20-23% less energy then a 10 SEER unit. 13 SEER will be the minimum efficiency standard by 2006.
R-22 is the most common refrigerant used in air conditioning systems.

Starting in January of 2010 manufactures will no longer be able to use R-22 in any newly manufactured Air Conditioning units. The new refrigerant, ozone friendly R-410, will replace the R-22.