What is the freon capacity for air conditioning system on a 1991 Chevy Blazer S-10 v6?

There's no single freon capacity for all 1991 Chevy Blazer S-10 V6s. The amount of refrigerant needed depends on several factors, including the specific model (there were variations within the S-10 Blazer lineup), the type of AC system (some might have had slightly different designs), and even the condition of the system (leaks can reduce the necessary amount).

To find the correct amount, you must consult your vehicle's owner's manual. This manual will specify the exact refrigerant type and the correct charge amount for your specific Blazer. Alternatively, you can often find this information on a sticker located under the hood, often near the radiator or AC components. The sticker may list the refrigerant type (likely R-12 originally, but possibly R-134a if it's been converted) and the charge amount in ounces.

Warning: Improperly charging an AC system can damage the compressor and other components. If you are not experienced with AC work, it's best to have a qualified technician service your system. They will have the necessary tools and knowledge to properly evacuate, recharge, and test the system for leaks.