Auto AC, R12 - R134a

A friend has been filling R12 systems on cars with R134a and says there is no need to evacuate out R12, he has done it for years on many cars. Is he lucky to not of had his friends cars damaged or can I just put in R134a in my R12 system without evacuating out R12.
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i was told always remove the R12, evacuate the system then add R134a and AC oil.
When a system loses gas it looses oil too. Not replacing the oil can destroy the compressor and if it disengrates thats basically the end of the AC
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Dont they add oil to the replacement 134a
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No, it is not automatically in there. If you look on the can some have it some don't, and you can buy just the oil as well.
On Sun, 28 May 2006 18:32:04 -0500, snipped-for-privacy@webtv.net (m Ransley) wrote:

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Hopefully someone with more expertise wil post, but certainly the two are not compatible as they act under different pressures.
For my 2 cents I think your friend has been lucky. Lets face it, how does someone determine their air conditioner needs help - when it's not cooling, usually at all. How many people do you know that say "I put a thermometer up to my a/c outlet and the air is 3 degrees warmer than it should be". Usually it's not blowing cold - e.g. out of R12. I have successfuly recharged empty R12 systems with R134 without replacing any parts. It is kind of silly, since I still don't determine what is wrong, but it's not in my daily driver so I don't worry. In addition it is not as efficient as swapping out the appropriate parts (and leaking ones...), but it will work at least decently. It has to be "under charged" as I believe you only use about 80 percent as much R134 pressure as you would R12. Even if you don't have the proper manifolds for measuring all of that the kits come with a small guage that does the trick.
Bottom line is you would not properly recharge a system if you don't create a vacuum in the system first, and if you create a vacuum I believe you would have evaculated all of the R12.
Finally, the oil used in R12 is not compatable with R134 so the system will fail sooner rather than later, if you don't evacuate that R12 oil and put in the proper oil.
On Sun, 28 May 2006 17:12:54 -0500, snipped-for-privacy@webtv.net (m Ransley) wrote:

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The EPA doesn't allow mixing refrigerants. To mix them violates federal law.
134A is not compatible with the old compressor lubricating oil.
Your friend may make AC that blow cold air, but he's also risking fine and prison.
--

Christopher A. Young
You can\'t shout down a troll.
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m Ransley wrote:

This procedure was listed on Interdymanics web site after R12 was discontinued. They make the freon. For conversion to R134A their instructions were:
1.    Vacuum the system removing all R12 and check for leaks. 1a.    Turn A/C on high setting. 2.    Insert one can of R134A oil charge. 3.    Bring system up to normal level using R134A. 3a.    Compressor should start turning. 4.    Check for leaks.
I've used this system for many years with no problems. Actually I still use my R12 gages on the R134A can. At your hardware store in the gas fittings you will find an adapter that fits on the R134A can piercer to the R12 hose. As the pressure on the low side tends to get near the normal level I monitor the temperature. When it gets to the normal cool setting, I quit adding. If you might not be the next person to add more freon make sure you indicate with a label somewhere under the hood that it's now R134a since you can't go backward to R12. If anyone has any problems with this method, look on Interdymanics Web site.
J
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