Thanks for good info on the certification process.
First, got a 1992 "anything"?, then the AC system is going to leak a little. That's life. So, what should you do about it? Well, I wouldn't spend a lot of money on the system if you can keep it working with minimal investment.
However, info on R12 to R134a was not so good, IMO.
Everyone is right, BUT, R12 to R134a conversions work just fine. The rhetoric about R12 being more effective than R134a is true, it's just that the difference is so small that you really can't tell the difference unless you are testing in a fully instrumented test lab. Want it cooler? Turn up the AC!
The oils are not compatible, that's true. However, know what difference it makes and what kind of catastrophy will occur if you just charge it with R134a? Nothing will change that you will be able to detect as a driver. Yeah, not compatible, but it works just fine. I have done many conversions but I no longer do this for profit, so I am not bound by the "How much money can I make on this guy's car" mentality.
Converting to 134a will seem just as cold to you as if you found some R12 to use.
I have R12 sitting in my garage. I kept it because of all of the original information, which the auto industry is all too glad to promote, that the conversion requires draining the R12 oil, flushing it out, etc., etc.
Now we know that it was not true. I converted my cars to cheap 134a for a couple of reasons, price and the environment. R12 is much less Earth friendly than R134a. So let's stop using R12!!
All you need to do about the old R12 is vacuum it out.
Also, what about the next time you need freon, in a year or two (figuring a 1992 car). You've polluted the air with R12 and now you are ready to do it again. Good reason to change to 134a.
Do you really want to pay ridiculous prices for R12 for the life of your car? Just switch it over now and be done with it.
I agree that normal leak testing should be done with any freon recharge. Also, you could have a worn out compressor, saturated dessicant, bad expansion valve, bad accumulator, etc/ etc. But if it doesn't work, it will not be because you used 134a.
Don't bother flaming, I am a retired factory technical rep for a top world auto manufacturer and I have heard all the "old mechanic" tales too many times.
I have no pride to maintain, no bones to pick. I just tell the truth from the engineers who know the real facts and let the chips lay where they fall.
Change over to 134a if you want to save trouble and money and the environment.
The 'Ole Factory rep