R134a and R12 are refrigerants. R134a supplanted R12 in late 1995 due to concerns over R12's effect on the ozone layer.
R12 is dichlorodifluoromethane (CCl₂F₂) and is classified as a chlorofluorocarbon (CFC). R134a is 1,1,1,2-tetrafluoroethane (CH₂FCH₃) and is classified as a hydrogenated fluorocarbon (HFC).
All gases, when allowed to expand rapidly, will decrease in temperature. This is the underlying principle on which most refrigeration and air-conditioning systems operate. Not all gases, however, will experience the same temperature decrease when allowed to rapidly expand. Gases are selected as refrigerants when they experience a greater temperature decrease than most other compounds (in addition to being nontoxic).
R134a and R12 exhibit similar performance characteristics as refrigerants, with R12 showing a slight advantage. R134a, however, is not a direct replacement for R12 due to incompatibilities in the compressor oils used for each refrigerant. R12 systems can be converted to R134a but special modifications to the system are necessary.
In the 1980s, environmental scientists discovered that R12 (among other CFCs) catalysed the destruction of ozone in the atmosphere. Most automobile manufacturers had, by the early 1990s, already transitioned to R134a. The production of R12 in the U.S. ceased in 1995. All R12 currently sold in the U.S. was either manufactured prior to the ban or has been captured and recycled.
R12 was originally discovered by General Motors' industrial chemist Thomas Midgley, Jr. in 1930.
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