* Leak Detection: Before adding any refrigerant, you *must* find and fix any leaks. Adding refrigerant to a leaking system is wasteful and environmentally damaging. Leak detection requires specialized equipment like UV dye and a UV light.
* Vacuuming: The system needs to be thoroughly evacuated (a deep vacuum) to remove air and moisture. Moisture in the system can cause serious damage and corrosion. This requires a vacuum pump capable of reaching a deep vacuum.
* Refrigerant Type and Amount: You need to know the *exact* type and amount of refrigerant your system uses (R-12 or R-134a – likely R-134a in a converted system, but possibly still R-12 if it hasn't been converted). Adding the wrong type or amount can damage the compressor.
* Specialized Tools: You'll need gauges to monitor pressure and temperature during charging, along with the correct fittings and hoses for connecting to the AC system. Improper connections can cause leaks and injury.
* Safety Precautions: Refrigerant is under high pressure and can cause serious injury if handled improperly. You'll need safety glasses and gloves.
In short: While it might seem like a simple task, improper AC service can lead to expensive repairs, environmental damage, and personal injury. It's far safer and often more cost-effective to take your 1991 Chevy Caprice Wagon to a qualified mechanic specializing in automotive AC repair. They have the proper equipment, expertise, and safety training to diagnose and fix the problem correctly.
