Would have been built for R12, can be converted to R134a.
There is only one Freon, and that is R12. R12 Freon came installed in your 1991 Chevy. It may or may not have been changed over to R134 Refrigerant. If not change it over, as the cost of R12 is unbelievably high an is no longer in production.
R134a freon......
It's R-134 and it is not freon any more.
FREON USED IS R-12
134A FREON IS USED.
Freon is not used in automobiles any more. Refrigerant is used.
R134a
R134a
R134a
R134A
134a
R134a