You are too kind.

 

snootsnout,
There's an old saying:
You attract more flies with honey than you do with vinegar.

You probably know your stuff pretty well. I'm not in a position to second guess that. But, to simply say that a conversion kit is all about folks trying to take money from unsuspecting / uninformed folks, might be undermining your own credibility.
As an engineering graduate, I understand some of what you say: being book smart does not necessarily make you practical smart, but it also doesn't necessarily mean you aren't!
To address a point you made. I can think of one reason to pull a vacuum for longer than 10 minutes even if the system hasn't reached atmospheric pressure. If the individual happens to be doing a conversion, then pulling a vacuum will help insure the elimination of the previous refrigerant by speeding boil off. Lower vapor pressure means lower boilg point, so the refirgerant gets completely eliminated by pulling the vacuum for a longer period of time. I'm betting you already know this, but others might not.
I think Dan was simply trying to exercise a little cautious discretion. Sort of a "caveat emptor" for those considering the repairs being discussed.
Thanks for your time. See you 'round!

 

How many people who are doing their own repairs to their vehicles are actually looking to do a permanent long term repair. Many of these folks are only trying to limp thier systems another year then they will get rid of the vehicle. Unfortunately they then complain that the system doesnt cool well. What do you want for a few cents on the dollar to what you should spend to fix it right the first time?

I can tell you that many vehicles that get a quickie Walmart kit to refill thier systems are only piling on the trouble, especially when thier systems are native R12 systems. The majority of the ones I see are well into the advanced stages of deteriation internally. Orifices clogged wth metal, fiber, and dessicant. Compressors that hammer when running due to bearing and internal component wear. Much of that wear occurs when a leak is present, and the oil leaks out with the refrigerant. The compressor with begin cycling off more often, but will continue to engage untill the system is nearly empty. All that time it is still engaging while low on freon, and more importantly while low on oil, it begins to come apart internally. All that metal and fibrous material, plastic, etc begins clogging the orifice and starts trapping in the condenser and clogging up resonance mufflers in the lines.

No amount of freon, whether you use R12 or R134 will compensate for an adequate repair of this problem. Failing to flush the system during the repair almost guaranteeing a reed valve seizure of a new compressor. I usually run a filter flush for one hour after repair, to get as much of the trapped metal from the condenser that may be residual after liquid flush or when light contamination is present. If the hoses have a muffler and the system had heavy contamination I replace that line, as well as any swelled up or oily leak evidence on the lines.

As for conversion a factory conversion is excellent. It usually includes a new condenser, high pressure cut off switch and wiring, and any adaptors necessary to install the appropriate switch and an R134 cycling switch. Some include a new fan shroud for added air flow performance. When adapted in conjunction with new compressor, accumulator, orifice and any other needed components this system will provide a long and effective repair and cool like an R134 system is designed to. Its not cheap, but if you are keeping your vehicle a long time its well worth the extra expense in the long haul, and improves the resale attractiveness to the future buyer.

When I repair a vehicle I have to look out for two people.. the vehicle owner, who deserves a proper and long term repair that he pays for, and for the company I work for, to give them a solid effective repair job that they wont have to worry about doing warranty work on shortly after repair. I work for both, and do my job with thier interests in mind, my future employment in mind, and pride of my work. In the long run it makes me far more than a quick buck.

Ive only been doing automotive AC work since 1979 so you can take this for what it's worth. I believe in fixing a vehicle right the first time. Anything less it tossing your money out the window.

Many repairs can be done far less expensively for temporary repairs, but in due time you will pay your due.