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#1193815 - 07/14/08 08:27 PM Why are R134a and mineral oil incompatible?
Big O Dave Offline


Registered: 08/10/04
Posts: 1415
Loc: The New State of Central Calif...
Other than "R134a and mineral oil are not supposed to used together in an automotive air conditioning system," what is the science behind this prohibition?

What does R134a do to mineral oil, or vice versa, when they are used together?

Specifically, we're talking about a R12 to R134a conversion, where a new (A6) compressor and dryer are being used. The A6 comes from Alma Products (the manufacturer of the compressor) with 10oz of mineral oil in it.

One of the biggest and most respected A/C shops in Simi Valley, CA says that there are no real problems with combining R134a and mineral oil, and an equally large and respected shop in Santa Clarita, CA says the same thing. Both have many years of actual experience with doing conversions and have seen few, if any, problems combining R134a and mineral oil with A6 compressors .

Then there are other, smaller shops which are philosophically "by the book," and say that PAG or ester oil MUST be used with R134a, and that mineral or ester oil MUST be used with R12.

My shop does not do A/C work and I know little about it, but I have to say that over the years I have seen that "book learning" may not always be the only right way to do things. Of course, I am asking for this information on probably the premier "I read it, so it must be true" forum, so I'll probably get some interesting responses.

Have at it!
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#1193820 - 07/14/08 08:36 PM Re: Why are R134a and mineral oil incompatible? [Re: Big O Dave]
TooManyWheels Offline


Registered: 02/21/03
Posts: 3710
Loc: Houston, Tex
Mineral oil does not mix with 134, so it does not flow through the system and lubricate the compressor. It can be left in the system in minute amounts when doing a conversion, as it will just find a low point in the system and camp there. I suspect this is what the first shop is referring to. For your own education, Google "R134a mineral oil miscibility".

PAG is the best 134 lubricant, but it is not compatible with mineral oil. Ester is the next best lubricant to PAG, and is compatible with mineral oil, so it is used when a system is converted from R12 and may have large amounts of mineral oil still in the system.

If they are talking about deliberately using mineral oil as the only lubricant, the only thing I can think of is that it is due to the ruggedness of the A6 compressor. I can tell you that a GM dealer mechanic did a warranty replacement of the compressor on my R134 97 Chevy pickup, and used mineral oil. That compressor died in short order. Mineral oil has a greater usability in the face of moisture contamination, but I have never heard of that justifying its use with 134.


Edited by TooManyWheels (07/14/08 08:45 PM)

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#1193834 - 07/14/08 08:51 PM Re: Why are R134a and mineral oil incompatible? [Re: Big O Dave]
MolaKule Offline


Registered: 06/05/02
Posts: 17734
Loc: Iowegia - USA
R134a is a 1,1,1,2-Tetrafluoroethane and its fluorene molecules are not compatible with the other hydrocarbon structures in mineral oils.

In a nutshell, PAG ester and polyol ester molecules are more compatible with the fluorene molecules.
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#1193838 - 07/14/08 08:55 PM Re: Why are R134a and mineral oil incompatible? [Re: MolaKule]
Big O Dave Offline


Registered: 08/10/04
Posts: 1415
Loc: The New State of Central Calif...
Wow! Thanks, TMW & Mola! Just the kind of info I was hoping for... I greatly appreciate it.
_________________________
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#1193863 - 07/14/08 09:32 PM Re: Why are R134a and mineral oil incompatible? [Re: TooManyWheels]
Big O Dave Offline


Registered: 08/10/04
Posts: 1415
Loc: The New State of Central Calif...
Here's the scoop on why I'm asking about this:

The A/C in my '76 Chevy wasn't working, because a seal in the compressor (the original one!) recently failed and let the R12 leak out. The A/C tech in the shop next to mine owed me a favor, and if I paid for a new compressor and a dryer, he'd install them and charge my system.

To make a long story short, my system is now charged with R134a and it has mineral oil in it. It was charged last Saturday afternoon, and now has, at most, 2 hours running time on it.

Can I just have the R134a evacuated and charge the system with R12, and call it good? Could I have damaged my new compressor is such a short time?

From what I read in the Google search recommended by TMW (thanks again!) R134a doesn't degrade mineral oil, it just can't mix with it and therefore distribute it around the A/C system.
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#1193882 - 07/14/08 09:45 PM Re: Why are R134a and mineral oil incompatible? [Re: Big O Dave]
TooManyWheels Offline


Registered: 02/21/03
Posts: 3710
Loc: Houston, Tex
The compressor should be fine, A6s are very tough. The only problem with switching back to R12 is that the port fittings have almost certainly been converted to the 134 standard, and I don't think they can be switched back. Since the system must be discharged, ask him to flush the oil and use ester. I am not sure of the appropriate weight, but I can look it up if you would like.

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#1193887 - 07/14/08 09:50 PM Re: Why are R134a and mineral oil incompatible? [Re: TooManyWheels]
Big O Dave Offline


Registered: 08/10/04
Posts: 1415
Loc: The New State of Central Calif...
 Originally Posted By: TooManyWheels
I am not sure of the appropriate weight, but I can look it up if you would like.


Thanks! I would greatly appreciate it if you would!
_________________________
“When you open your heart to patriotism, there is no room for prejudice.”

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#1193907 - 07/14/08 10:11 PM Re: Why are R134a and mineral oil incompatible? [Re: TooManyWheels]
Rock_Hudstone Offline


Registered: 11/13/07
Posts: 1194
Loc: New Jersey
 Originally Posted By: TooManyWheels
The only problem with switching back to R12 is that the port fittings have almost certainly been converted to the 134 standard, and I don't think they can be switched back.

Use adaptors and recharge with R12 if you can get it at a reasonable price.

Your already half way home with the mineral oil in there, and R12 will yield better cooling performance and lower head temperatures.

Moreover, flushing is pain in the a$$. The compressor will have to be removed and drained, probably the drier as well since a portion of mineral oil resides in there also, or perhaps replaced again.



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#1193931 - 07/14/08 10:35 PM Re: Why are R134a and mineral oil incompatible? [Re: Rock_Hudstone]
TooManyWheels Offline


Registered: 02/21/03
Posts: 3710
Loc: Houston, Tex
The ester oil weight for an A6 compressor is 100.

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#1193933 - 07/14/08 10:39 PM Re: Why are R134a and mineral oil incompatible? [Re: TooManyWheels]
Big O Dave Offline


Registered: 08/10/04
Posts: 1415
Loc: The New State of Central Calif...
 Originally Posted By: TooManyWheels
The ester oil weight for an A6 compressor is 100.


Thanks for digging this up.

Regarding going back to R12, aren't the port fittings on the dryer? If so, a dryer is only $27, so that would be pretty reasonable. Or am I missing something... (other than the incredible cost of R12)...
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“When you open your heart to patriotism, there is no room for prejudice.”

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#1193934 - 07/14/08 10:40 PM Re: Why are R134a and mineral oil incompatible? [Re: Big O Dave]
TooManyWheels Offline


Registered: 02/21/03
Posts: 3710
Loc: Houston, Tex
The high side line has a fitting also. As I recall, that is a short, simple hose, so it might not be too expensive either.

You are not missing anything. The only thing we haven't talked about is R12 compatibility of the compressor seal and dryer, but I believe those have all been dual-compatible for some years.


Edited by TooManyWheels (07/14/08 10:43 PM)

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#1193950 - 07/14/08 11:09 PM Re: Why are R134a and mineral oil incompatible? [Re: TooManyWheels]
Big O Dave Offline


Registered: 08/10/04
Posts: 1415
Loc: The New State of Central Calif...
TMW, you are awesome for your timely help!
_________________________
“When you open your heart to patriotism, there is no room for prejudice.”

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#1193964 - 07/14/08 11:37 PM Re: Why are R134a and mineral oil incompatible? [Re: Big O Dave]
TooManyWheels Offline


Registered: 02/21/03
Posts: 3710
Loc: Houston, Tex
Anytime!

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#1194043 - 07/15/08 05:21 AM Re: Why are R134a and mineral oil incompatible? [Re: TooManyWheels]
punisher Offline


Registered: 09/11/04
Posts: 2349
Loc: snowblind in TX
A6s are a special case as they have their own oil sump as well as an internal oil pump. They tend to be more forgiving than compressors that rely solely on a refrigerant/oil slurry for lubrication.

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#1194717 - 07/15/08 09:53 PM Re: Why are R134a and mineral oil incompatible? [Re: punisher]
The Critic Offline


Registered: 08/30/04
Posts: 19023
Loc: Walnut Creek, CA
To answer the original question, I'm not sure. I've always been told that they are not. However Toyota Service Bulletin AC002-98, which covers R134A A/C conversion on R12-equipped models, clearly states to install PAG oil during the conversion but a system flush is not necessary.

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