All classic car original air conditioning systems were filled with dichlorodifluoromethane or R-12/CFC-12 Freon. Even newer cars used the standard R-12 until the EPA, under section 609, in an attempt to reduce atmospheric ozone depletion, mandated that manufacturers phase out its use by the end of the 1994 model year. An environmentally friendlier substitute, tetrafluoroethane or R134A, was selected as the new industry standard, and plans were to phase out R-12 manufacture entirely by 1996. At the same time, new regulations regarding recharging of the older air conditioning systems on classic cars were also mandated. Original R-12 systems were to be retrofitted to accept the R134A refrigerant. The changeover kit depended on the original manufacturers' components, but basically consisted of adapters for connecting the older R-12 charging ports to the new R134A charging hoses and manifolds. A filter drier changeover was also done and once the old R-12 was purged from the system (hopefully through an MVAC refrigerant recycler), a new R134A-compatible PAG oil was added to the system for lubrication before the system was refilled.

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