Automotive Air Conditioning Information Forum

Hello!

Im doing a big service on the ac system, and thinking about filling it with PAO 68 oil from manufacturer Hella. Originally the system is filled with ND8 oil, witch according to denso is equivalent to double capped PAG 46. The PAO 68 oil is, according to Hella, said to have the benefits of being non-hydroscopic. So if the system in the future would ever to be opened to atmosphere for a longer time, the oil wouldn't be affected and no need to change it with a system flush. The oil is also non agressive to the rubber seals in the system, witch would eventually keep the system closed and working for a longer period of time. AC systems often stoppes working because the seals gone bad so the refrigerant (R134a) leaked out. It seems that the PAO 68 is a much better oil and will work flawlessly in my system. BUT when asking a mechaic the answer is nono, it is a universal oil and I'm better of using the original ND8 oil.

Anyone with a good explanation to witch oil is the better choice?

I have never seen a PAO that was miscible with 134a. PAO is ok with R12 & HC's

134a should use PAG, or if you want a substitute POE. DEC PAG oils are not hygroscopic, so there is no reason to fear them.

bohica2xo wrote:I have never seen a PAO that was miscible with 134a. PAO is ok with R12 & HC's

134a should use PAG, or if you want a substitute POE. DEC PAG oils are not hygroscopic, so there is no reason to fear them.

My understanding is that the POE oil has no benefits over the PAG more than it is not conductive for electricity. And the DEC PAG oils are hydroscopic, the hydroscopic process is just dramatically slowed. See:

http://docs.lib.purdue.edu/cgi/viewcont ... ntext=icec

According to manufacturer Hella, the PAO oil will only slightly mix with the refrigerant. They states that this is wanted because it will keep the oil where it is needed ( in the compressor ) and make the ac system more efficient not having to circulate unnecessary amounts of oil.

However an logical statment was put by YouTube user John Doe in the comments to this video about PAO oil:

https://youtu.be/YKWA_XAKdtw

Part of John Doe's comments:
"My car compressor is mounted horizontally and NOT at the lowest level in the A/C circuit.
As far as I know, the compressor does NOT prevent it's lubricating oil be pumped out together with the refrigerant (mix & travel).
Question: What will keep this 'non mixing PAO oil' inside the compressor if not gravity ? (and not be pushed out of it and accumulte instead at the lowest point in the circuit.. = no lubrication)."

"I searched whether this mixability (in the automotive A/C) is good or bad, and I WAS RIGHT - The mixability of the oil with the refrigerant IS CRUCIAL for the lubrication of the pistons. These AC car pumps don't have an isolated carter (low pressure refrigerant goes even behind the pistons) and they are not installed at the lowest point in the circuit (= no help from gravity either) so the 'mix & travel' is the only solution that guarantees some lubrication. However, I'm sure that in a kitchen vertical fridge this 'less mixable oil' will do miracles."

With this I see my question as answered by John Doe.

Thank you

These posts are beginning to look like spam for some snake oil...

Here is the test for water in PAG oils:
http://www.autoacforum.com/messageview. ... adid=17571

That .edu paper is not particularly applicable to the real word, like much of ,edu

POE oils are miscible with both R12 & 134a, and THAT is the applicable part for MVAC.

bohica2xo wrote:These posts are beginning to look like spam for some snake oil...

Here is the test for water in PAG oils:
http://www.autoacforum.com/messageview. ... adid=17571

That .edu paper is not particularly applicable to the real word, like much of ,edu

POE oils are miscible with both R12 & 134a, and THAT is the applicable part for MVAC.

In my post the PAO oil was said to be not usable in vehicle ac, atleast when using refrigerant R134a, how is that in anyway spam for snake oil?

Thank you for your test.

That .edu paper Is based on observations in this world, with specified temperature and humidity. It proves that DEC PAG oil is very much tolerant to moisture and is the preferred oil to use. That the paper is not particularly applicable is only an opinion of yours. With your way of thinking I can state that neither of the tests, both yours and the one made by Purdue university, are not particularly applicable to MVAC systems. This because none of the tests is made with the temperatures, pressures and other chemicals in a "real world" MVAC system.

Yes POE oil also does mix with both R12 and R134a? Thank you for the information, it is however not relevant in this case because I was asking if the PAO 68 oil is an better alternative to the ND8 oil. My ac system use R134a and does not use an electric compressor. The POE oil is therefore not an better alternative in my system. POE oil also does not (according to manufacturer Denso) mix well with the ND8 left in my system, I would then require an complete system flush to avoid compressor failure.