Can You Mix Freon Types?by Rebekah Richards
Freon refers to a brand name of several chlorofluorocarbons (CFCs) used as refrigerants in the air conditioning systems of most cars and trucks built before 1994. Freon should not be mixed with different types of Freon, other CFCs or alternative refrigerants.
After scientists discovered that Freon and other CFCs deplete the ozone layer, the 1989 Montreal Protocol sharply limited the use of CFCs. Automobile owners must use an alternative refrigerant to repair systems that relied on Freon.
Some refrigerants are marketed as "drop-in" refrigerants that are similar enough to Freon and other CFCs that you can mix the refrigerants or use the new refrigerant without modifying the air conditioning system. According to the Environmental Protection Agency, mixing refrigerants may damage your system. In addition, it is illegal to insert a new refrigerant before extracting the old refrigerant.
Scientists have developed alternative refrigerants that do not damage the environment, but you must replace all or part of the air conditioning system before using an alternative refrigerant. Replacing part of the system is called a "retrofit" and costs less than purchasing a new system.