The production of R12 was banned in 1993 and most manufactures started using the new R134a from 1994. The use of exsting stock of R12 was banned from 2001. R12 and R134a do not mix and the only correct way to recharge a R12 system is to have it converted to R134a, there are some so called drop in replacements about but you need to be careful as some are inflammable.