You can receive up to a $1,500 instant rebate for trading in your old  air conditioner.  So if your AC unit is more than 10 years old it might be time to have it replaced with a new energy efficient unit.  Today’s air conditioners use 30% to 50% less energy to produce the same amount of cooling as air conditioners made 20 years ago.  In fact, air conditioners that were manufactured after January 26, 2006 have to have a SEER rating of 13 or higher.  SEER stands for seasonal-energy-efficiency-rating.  SEER 13 is 30% more efficient than the previous minimum SEER of 10 that earlier models have.