When replacing R12 freon with another, you will need to dispose of any R12 remaining in your AC system. This will require an R12 recovery machine, which is available in mechanic shops specializing in AC because it is illegal to release R12 directly into the air. Many freon substitutes will require new parts or oil before they can be used with the system. This should be done by a professional. Once the R12 is removed from the system, you can fill the AC system with new freon.
Replace R12 freon with Hot Shot R-414B. This product is one of the EPA's recommended substitutes for R12 and can be incorporated into an R12 system with a retrofit kit. All the R12 will need to be removed from the system by a professional. Hot Shot guarantees that it will get your vehicle 10 degrees colder than R12. You will need to replace your gauges.
Replace an R12 freon with Freeze-12. Freeze-12 is allowed by the EPA and is more environmentally friendly. Freeze-12 claims to outperform R-134a and R12. This freon also works with existing R12 lubricant, and you can refill your current system with standard R12 gauges.
Replace R12 freon with HFC-134A. The HFC-134A freon is not compatible with the compressor oil required for R12. Your AC system will need to be completely drained, and a vacuum pump will need to be connected to evacuate the system. A new filter and adapter fittings will also need to be installed. You will also need the correct type and amount of oil, which is dependent on the size of your AC compressor.
