You cAnt sorry
You do not want to buy Freon as it is very, very, expensive. Have the leak repaired, the system purged of all Freon R12 and the oil. Have it converted over to R134 refrigerant. You cannot just add R134 as the oil used in R12 is not compatible with R134. You will be money ahead by converting it.
no
They should never be mixed.
Freon R12 refrigerant is so very expensive that I recommend you have the A/C converted to R134a. But first you must have the leak repaired. The shop will then remove any R12 left in the system, flush the system to remove the old oil, install fresh oil that is compatible with R134a, and charge the system. If there is any R12 left they may pay you to recover it.
1993-95 for most.
Freon R12
r12
R12
Contains no (R12) Freon. Freon was banned in 1996.
R134a Freon is an oxymoron, Freon is R12 but the answer is yes, a subtle 'sweetish' odor
There were some R134a units in 1992, but they were not the norm. Most likely, you have an R12 unit, which requires retrofitting in order to be compatible with R134a.