A lot of folks say 134 ain't as cold as R-12. This is to be expected if you convert a 12 system to use 134. In a system intended for 134, 134 works well. The two types of refrigerant have different pressure ranges at which they function properly, and I believe it's 134 that runs at a higher pressure, so if you convert a 12 system to 134 you should be really sure it doesn't have any leaks. Evacuate the old R-12, pull a good vacuum and make sure it holds. Then you can go ahead & do the conversion with the different fittings, oil, dryer, etc. But don't be shocked if you find it necessary to recharge more often. Check out the forum at
www.ackits.com - those guys are AC nerds. Of course I mean that in a good way.
I took the $15 exam to get my 609 certification. The web site is
www.macsw.org, and a 10 year old could pass the open-book test. This certification will allow you to *legally* purchase genuine R-12 (from places like Ebay) for about $15/can. Compare this to my local mechanic who wanted $50/can <img src="/forums/images/graemlins/shocked.gif" alt="" /> You make up the cost of the test on your first can. My '85 has a small leak somewhere, small enough that it couldn't be pinpointed using the UV tracer dye or the little sniffer device. It needs a can about every 3-4 years, so with my 609 certification it's not that expensive at all. I opted for this route rather than a 134 conversion, and I'm way ahead (dollar-wise) so far. If my leak gets much worse I may have to think about converting; there's a certain point at which it does become too hard on the wallet, and on the ozone layer. <img src="/forums/images/graemlins/cheers.gif" alt="" />