if u have not done any work on the a\c before and u need to "add coolant" then u more than likely have leak somewhere wich needs to addressed first.
R134a
It takes r134a refrigerant.
Chevy switched from R12 to R134a for the model year 1994. Your truck should be R134a.
Probably r134a.
R134a
r134a
R134a
R134a refrigerant.
R134a
R134a Refrigerant
R134a.
r134a