How do you change the R12 to 134 in a 1993 Chevy silverado?

You can't simply change an R12 system to R134a in a 1993 Chevy Silverado by just adding refrigerant. R12 and R134a are chemically different and have different operating pressures and lubricating properties. A direct swap requires a conversion kit and significant work. Attempting a direct swap without conversion is extremely dangerous and can damage your vehicle's AC system.

Here's what a proper conversion entails:

* Oil Change: R12 systems use mineral oil, while R134a systems require ester-based oil. All the old oil must be completely flushed out of the compressor, condenser, evaporator, and lines. This requires specialized equipment to evacuate the system and ensure complete removal.

* O-ring Replacement: R134a requires different O-rings that are compatible with the new refrigerant. All O-rings in the system need replacement. Some seals may require replacement as well. These are made of different materials to prevent leaks and damage from the new refrigerant.

* Expansion Valve/TXV (Thermostatic Expansion Valve) Check/Replacement: The expansion valve in an R12 system may not be compatible with R134a. It might need to be replaced or at least thoroughly checked.

* Compressor Compatibility: While some R12 compressors *might* work with R134a and the correct oil, it's not guaranteed. It's best to ensure the compressor is compatible with R134a and the new oil. Often, a new compressor is the safest bet.

* Refrigerant and PAG Oil: You'll need the proper R134a refrigerant and PAG (polyalkylene glycol) oil.

* Leak Testing: The entire system must be thoroughly leak-tested *before* adding any new refrigerant. Leaks are common, especially after working on the system.

In short: This isn't a DIY job. It requires specialized tools, knowledge, and experience in automotive air conditioning repair. Attempting this conversion without the proper expertise and equipment can lead to costly repairs, system damage, and even injury.

Recommendation: The best course of action is to take your 1993 Chevy Silverado to a qualified automotive air conditioning specialist. They will have the necessary equipment and knowledge to perform the conversion safely and correctly. They may also advise on whether a complete R134a retrofit kit is the most cost-effective option compared to just repair of the existing R12 system. Consider that the cost of a professional conversion might be close to the cost of replacing the entire system.