The first widely used refrigerants were chlorofluorocarbons, also known as CFCs.

In the 1970s, however, the scientific community determined that CFCs were building up in the Earth’s upper atmosphere in a way that damaged the ozone layer, lessening the planet’s natural protection from some forms of solar radiation. In 1987, 27 countries therefore signed a global environmental treaty called the Montreal Protocol to Reduce Substances that Deplete the Ozone Layer. Under this treaty, signatories pledged to reduce the use of ozone-depleting compounds (such as halons and CFCs) to below 50% of 1987 levels by the year 2000.

One of the most widely used replacements for CFCs were chemicals known as hydrochlorofluorocarbons (HCFCs), and this substitution largely made the phase-out of CFCs possible. Unfortunately, many HCFCs, including HCFC-22 (a principal component of the trade name product “Freon”) contribute both to global warming and can, to a lesser degree, serve to deplete the ozone layer as well.

For this reason, Montreal Protocol signatories agreed to accelerate the phase-out of these products in 2007. In the United States’ case, this meant that the Environmental Protection Agency (EPA) mandated no new HCFC-22-based air conditioning systems be manufactured or installed after 1 January 2010, and the import or production of HCFC-22 be completely halted a decade later.

The regulation put in place an HFC phase-down from 2015 to 2030 by means of a quota system and sectorial bans on high GWP refrigerants

Newer A/C machines are required to use ozone-friendly refrigerants.