Refrigerant is in the A/C system to remove heat. During operation the refrigerant cycles through the system changing from a liquid to a vapor (absorbs heat) and then a vapor to a liquid (dissipates heat). The most common automotive refrigerants are R-12 and R-134a. R-12 was used extensively in automobiles until the early 1990s. R-134a, a more environmentally friendly refrigerant, was phased in to replace R-12. R-134a is still a contributing agent to global warming when released into the atmosphere. New refrigerants, such as R-1234yf and R-744, are being introduced to replace R-134a. You should not perform air conditioning work unless you have a special machine to recover and recycle the refrigerant and you have been trained and certified to perform this type of procedure. Service technicians are required by law to recover and recycle refrigerants in an effort to protect the environment.