What is required to change a 1991 Geo Tracker to r-134a?

To convert a 1991 Geo Tracker to R-134a refrigerant, you need to replace the existing R-12 refrigerant with R-134a, which requires retrofitting the A/C system. This includes replacing the receiver/dryer, expansion valve, and O-rings with R-134a compatible components. Additionally, you will need to drain the old refrigerant, flush the system to remove any contaminants, and then charge the system with the appropriate amount of R-134a. Finally, ensure that the A/C system is leak-free and functioning correctly before use.