It is probably R-12, the stuff you can't get anymore. Look at the A/C fittings where you would fill it. If the threads are on the outside of the fitting, it is still R-12. If the outside is fairly smooth and you see the threads in the center of the fitting, it is now R-134a.
What is specified in your owner's manual.
The proper charging kit for a 1994 Chevy s-10 is a 134a - NOT a R-12. You can purchase this charging kit from most automotive stores.
R134aR134a
R134a
R22
R134A
r134a
R134a
R134a
R134a
134a
R134a