You should NOT attempt to add refrigerant yourself unless you have the proper equipment and knowledge. Adding refrigerant incorrectly can damage the system and lead to expensive repairs. The system needs to be properly diagnosed to determine if it simply needs a recharge, or if there's a leak requiring repair before recharging. Low refrigerant is usually a symptom, not the problem itself.
Improperly adding refrigerant can be dangerous due to high pressure and the potential for eye injury.
Instead of trying to add refrigerant yourself, take your S10 to a qualified mechanic or an automotive air conditioning specialist. They have the tools and expertise to properly diagnose and repair your AC system. They'll use gauges to check pressure and determine if the system is holding charge, and what may need to be repaired.
