Most air conditioners use one of two types of refrigerant: R-22 and R-410A. If your air conditioner was manufactured before 2010 then there is a good chance it uses R-22 which is starting to increase in price. The US has agreed to phase out R-22 due to the damaging effect it can have on the ozone layer. R-22 is going to become more scarce in the future. Look at the label on your air conditioning unit and if you see R-22 listed, you should hire a qualified heating, ventilation and air-conditioning (HVAC) contractor to do a tune-up on the AC system and verify there are not any leaks. This will prolong your system and help reduce future repair costs.