What kind of Freon goes into a 1994 Chevy S-10 pickup?

A 1994 Chevy S-10 pickup truck likely used R-134a. While R-12 was common in earlier vehicles, R-134a largely replaced it by the mid-1990s. However, it's always best to check the sticker on the underside of the hood near the radiator. This sticker will definitively state the refrigerant used in that specific vehicle.