The most commonly used refrigerant in air conditioners is R-22, or Freon, as of 2015. Freon is being phased out from use due to the harmful effects on the environment it creates and should be phased out completely by 2020, according to the U.S. EPA.
As of 2015, the most common alternative to Freon being used is R-410A. R-410A is environmentally friendly and causes no harm to the ozone layer. Other common alternatives to R-22 include R-407C, R-438A and R-422. Existing systems designed for R-22 use cannot substitute alternative refrigerants without risk of damage to the unit. The manufacture of systems using R-22 is prohibited, as of 2010.