Mazda B2200: Convert from R12 to R134?

The factory R12 A/C system on my 1988 Mazda B2200 has had a slow leak for the last 10 years. Normally adding one small can of R12 in the
Spring would get me through until the next year. Last year the small leak apparently became a major one: the sight glass looks like all the freon is gone and the A/C doesn't cool at all. The compressor kicks in normally.
Given the high cost and scarcity of R12 (I'm down to my last 3 small cans) I'm wondering if I'd be better off having a professional A/C shop convert the system over to R134 after they locate and fix the source of the leak. An article which came out in Family Handyman or some such do-it-yourself magazine back in the 90s listed the B2200 as one of the more expensive models to convert, because major components have to be replaced along with the O-rings. However, people lately have told me it's not as big a deal as it was once made out to be, at least for most makes/models, and on most cars the R12 components will work with R134.
Can any of you refrig techs or fellow B2200 owners give me the straight story, and tell me approximately how much the conversion job would cost assuming the leak is just a bad O-ring or seal?
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On Fri, 21 Sep 2007 14:03:32 -0700, snipped-for-privacy@fastmail.fm wrote:

Fix the leak and leave it charged with R12. It will cool better and be less prone to future leakage. Total cost will probably be considerably less than converting it. R12 is still available. I have it and could easily buy more if I wanted.
Don www.donsautomotive.com
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Don wrote:

"Easily"? Must be nice to be able to conjure up a wheelbarrow full of Euros any time you want. :)
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It's available in large and small quantities on Ebay for not all that much money. People are still finding stashes of cans in their garage.
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considerably less than converting it.
Don, would any major components have to be replaced to convert it to R134, or just O-rings, valves etc.?
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snipped-for-privacy@fastmail.fm wrote in news:1190427871.690771.156520@ 19g2000hsx.googlegroups.com:

Besides the cost, there's something like a 20% reduction in cooling efficiency with the conversion to R134a. I'd leave it R12 if I were you.
--
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The issue is that it's usually _cheaper_ to replace major components. For example, you can take the compressor apart, replace the various rubber seals in it, clean the oil out, and put it back together, and it'll only cost you a few dollars in parts and a whole lot of labour. If your labour is free, by all means do this. But if you're paying for labour it might just be cheaper to drop in a new compressor.
R12 was frightfully expensive for a few years after it got taken off the market, but prices stabilized and then have dropped considerably. It's still more expensive than R134A, but it's not anywhere near as expensive as it used to be. So there isn't as big a reason to change things over as there once was. --scott
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On Fri, 21 Sep 2007 19:24:31 -0700, snipped-for-privacy@fastmail.fm wrote:

My shop does not do conversions. I bought plenty of R12 when I saw the handwriting on the wall. I am not that impressed with the cooling performance of most conversions I see, nor their ability to contain refrigerant. Drier is probably not compatible. "O" rings, hoses, expansion valve will all get by but they are NOT optimal for HC134. Hence less cooling, more chance of leaks. Wholesale suppliers still offer to sell me R12.
Don www.donsautomotive.com
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