What kind of freon is used in a 1994 Chevy 2500 pickup?

94 is the year most vehicles were in the change-over stage from the factory from r-12 to r134, look for a yellow tag/stick under the hood as to which is in your system. It came from the factory with R12 Freon installed. Unless it has been converted to R134, then it still has R12. Due to the extremely high cost of R12, I suggest you convert it over to R134a.