Compressors

• A typical air conditioning (AC) system includes an outdoor unit that contains a refrigerant compressor and condensing coil. The compressor motor functions as a pump to compress a refrigerant gas into a high pressure at a higher temperature, which is cooled to a liquid state, cooling the interior of a home.
  
  

SEER Rating

• Air conditioning systems are rated by their seasonal energy efficiency ratio (SEER), which indicates the amount of energy needed to produce cooling. According to the U.S. Department of Energy, older AC units typically have a SEER rating of 6 or less. The minimum SEER rating allowed, as of 2010, was 13. According to the California Energy Commission, the highest SEER rating available is 23.
  
  

Considerations

• The Department of Energy advises homeowners looking to upgrade their outside compressor unit to a higher efficiency model to first verify that the new compressor matches the efficiency specifications of the indoor unit, which could be either a furnace or an indoor evaporator, depending on the homeowner's setup.