The newer units of central air conditioners have a very high efficiency rating (SEER). The air conditioners are appliances which dehumidify and extract heat from the air in an area, thus cooling it, and in the winter they have an electric heating unit to warm the air. Most units have a refrigerating cycle with a compressor in the outside of the building and the air handler with the evaporator and a powerful blower inside the house. This chilled or warm air will be distributed throughout the house by means of ducts and grids. In addition, a filter or filters are used to collect dust and lint from the air returned to the air handler to be recycled again. However, the most important precaution if the unit is not cooling well is to inspect the duct system in the attic for leaks, faulty installation and or lack of insulation of the ducts and if the ceiling insulation is poor or insufficient. If this is faulty, even a high efficiency central unit won't be doing its job and you will be wasting money trying to cool or heat the house.
It is also important to check the thermostat so that it is working properly.
