Freon R-12 Replacement

Q: Freon R-12 Replacement

I know that there were some in the group very knowledgible about A/C from some previous discussions and I know very little about A/C systems.

I heard from a mechanic that requiring R-12 to be purged from a system before installing R-134A is a hoax. He said that R-134A could be put into an existing R-12 system that is low.

Do these refrigerants mix? What would happen to the system if they were mixed? Regardless of the freon. What are the recommended pressures on the low and high sides. I have a 89 chevy that is low on freon and do not want to fill it with the incorrect freon or fill it too high. This will also come in handy when I replace the A/C unit on my bird.

A: The two freons are compatable. Some of the blends out there called R-12 substitutes actually contain both R-12 and R134A as well as other gasses such as butane(not safe). The problem is the oil. R134A is not compatible with the oils used in R-12 systems. The oil must be soluable in the refirgerant so it can flow with it and therefore lubricate the system. The correct way to change the system to R134A is to remove the compressor and drain it. Then flush all the lines with solvent. Removing about 80 to 90 percent of the old oil is acceptable. Refill the compressor with the correct oil, PAG or Ester oil, and reassemble. Evacuate and recharge with R134A.

I have seen conversion kits at some of the discount auto parts (Auto Zone, etc.) that have an oil that you meerly add to the system and it suppossedly changes the oil so it works, but none the seminars I have attended could recommend such an additive or even understand how it could work.

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