TheSamba.com :: View topic - Flushing PAG from new AC compressor to use mineral oil

Tue Jul 27, 2021 4:02 pm

Hi,

I rebuilt my AC system (87 Syncro) last fall with the intent of using red tek and my original compressor. I assembled my new system with mineral oil as that was in my compressor and it's fine with red tec.

I later decided to also replace the compressor, so now I have a compressor filled with PAG.
I can't seem to find any real consensus about how to flush the PAG. Some people say just drain the PAG and fill with mineral, spin the compressor a bit, drain and repeat a couple of times. Others have suggested flushing with ester first as it is compatible with both PAG and mineral.

Anyone done this? I suspect that flushing a few times with mineral before the final fill would probably be fine, but I'd hate to gum up a new system if that is the consequence of doing it wrong.

Thanks.

Tue Jul 27, 2021 4:23 pm

I'd pull the plug and let it drain over night.

Flushing with the oil you want to use makes sense to me.

I found it surprising how much oil this system requires!

Dave

Tue Jul 27, 2021 4:46 pm

Thanks - Thats a good call. I just pulled the plug and left it for the night.

I did the initial drain a little earlier and I mixed some PAG with some mineral in a small container. It didn't explode or turn to concrete, so flushing a few times with mineral seems ok. When I put the system together, the smallest quantity of mineral oil I could get was a gallon, so I've got plenty to flush with :)

Tue Jul 27, 2021 5:19 pm

I would drain the case through the drain plug first. Then take the refrigerant line plugs off, place them downwards and turn the compressor shaft. There is always more oil but that should get most of it. Discretion is probably the better part of valor here.

Tue Jul 27, 2021 5:46 pm

Another good call - Thanks!

Wed Jul 28, 2021 2:32 pm

pag and mineral are NOT compatible AT ALL

it will make jello

i would drain the PAG and use ester as it's compatible

or make dam sure you have all the PAG out of the compressor using a flush agent

Wed Jul 28, 2021 11:15 pm

I've used rubbing alcohol and compressed air to flush compressors of residual PAG.

Thu Jul 29, 2021 1:34 pm

I went into this fully expecting to find some appropriate flush agent - but all I could come up with is statements like "under no circumstances should you put any kind of solvent into a compressor". I understand blanket statements like that are to protect people from mishaps do to the variables involved. Certainly there is some solvent that can make brief contact with seals and not damage them, but I'm surprised that I can find no discussion.

So far I have drained the PAG, filled and flushed with mineral oil (spinning the compressor) about six times. The mineral oil now drains out nice and clear. I would still flush it with a solvent to be safe.

Zeitgeist - I'm glad to hear about the alcohol. Did you do this on a new compressor? (VAG alcohol?) :)

Skills - do you know of an appropriate solvent?

Thanks

Thu Jul 29, 2021 1:43 pm

Do no harm.

Step away from flushing. I think you are just entertaining trouble.
You drained it, you flushed it multiple times, you are good.
Go run it!

Dave

Thu Jul 29, 2021 2:28 pm

A while ago there was a thread about cleaning the whole system out (except the dryer) by an old timer here. He recommended going to a truck/travel place and getting a jug of Air Brakes System cleaner. I don't know what it is, but you might search for a thread about it, and look for a post by Terry Kay

Thu Jul 29, 2021 3:01 pm

Thanks - I have read TK's threads and did use air brake cleaner to flush my evaporator.

Most flushing discussions are about flushing/cleaning the system excluding the compressor.

I guess what I really need to know is what turns what to goo. When going from mineral to PAG, which is what all the discussions are about, it seems to be accepted that you can have up to 5% residual mineral oil in your PAG and not have a gelling problem. So in that case the flushing method that I used would be ok.

The reverse could be a different story if it is the mineral oil that turns the PAG to goo. If I have any residual PAG there will certainly be much more than 5% ratio of mineral oil present. Does that mean that even a trace amount of PAG will eventually turn to something that will clog my system?

My big mistake was not deciding to replace the compressor in the first place. I could have just coverted to PAG when I assembled everything - but that ship has sailed.

Thu Jul 29, 2021 3:01 pm

The old Terry Kay method, which I have used before, is to use truck air brake antifreeze solution to clean out your AC lines. It does work well for this purpose. I have run it through all components except the compressor.

It works like this: you pour the solution in to a container that can be pressurized. Put the cap on the container and pressurize it with an air compressor. Open your AC system and make sure the solution has a place to go--usually placing an open hose in a bucket. Place the nozzle of the pressurized, loaded container on the open hose and open the nozzle jet. The solution will blast out of the container and through the hose and into your bucket. Use additional compressed air directly in the AC hose to blast out any remaining solution.

There are specialty products from Intermatics that do the same thing. I find that the air brake antifreeze is more available over the counter at my local auto parts store (O'Reilly).

kourt

Thu Jul 29, 2021 3:08 pm

Terry Kay recommended air brake antifreeze. I have used it to flush AC lines. It works. Most FLAPS will sell it. The question, as DJKeev has identified above, is whether it will be needed.

There are so many crevices in the compressor where PAG oil could hide that I do think flushing with such a fluid is a good idea to get the PAG out. The air brake anti-freeze typically is mostly methanol. It will remove most of the old oil and if you hit the compressor with compressed air, it will mostly evaporate. The remainder of evaporation (if any) of this liquid will occur when you vacuum the system.

The key thing, if you go this route, is to get the compressed air into the compressor ASAP, repeat the fluid flush again if you choose, compressed air again, and then add your final oil, drain, and add again.

The air brake line antifreeze typically is 60 to 100% methanol. Methanol corrodes aluminum, which is what the pistons and compressor case are made of. This is why you need to blow compressed air through the compressor and then fill with your final oil ASAP if you use air brake antifreeze. Do any such flush outdoors. Wear gloves and a respirator. Methanol is not to be trifled with. If it lights up, you won't see the flame. Keep a garden hose or fire extinguisher close by.

I would never mix these two kinds of oil, PAG and mineral. For what it is worth, PAG is actually a great lubricant and works well with RedTek or R134A.

Thu Jul 29, 2021 3:23 pm

Dave - I'm kind of with you on the just run it, there cannot be much PAG left in there. I'm just trying to dig up as much actual experience as I can before pulling the trigger. I like that Casey has successfully used alcohol. As of now that's my back up plan if I chicken out on the just run it plan.

Thu Jul 29, 2021 3:29 pm

Is the Methanol ok for the seals and is it just aluminum corrosion that is the concern?

Thu Jul 29, 2021 3:56 pm

Don't overthink this.

Thu Jul 29, 2021 3:59 pm

djkeev wrote: Don't overthink this.

Ha - Impossible. :)

Thu Jul 29, 2021 4:14 pm

Yes, I flushed the new AC compressor for my TDI Vanagon with rubbing alcohol. I didn't invent this process. It's been used for decades.

Thu Jul 29, 2021 6:39 pm

rubbing alcohol contains water.

Methanol does not.

Methanol is fine to flush lines and compressors.
Make sure you drain ALL of it out,
then run compressed air to evaporate any traces.

Don't overthink it.
A couple hours of methanol exposure will not
dissolve your seals or compromise aluminum.

You'll be surprised how much 'snot' comes out of
the compressor and the lines, old yellow flourescent dye, etc.

Thu Jul 29, 2021 6:47 pm

Rubbing alcohol also evaporates quite quickly, especially when exposed to compressed air rushing by. Any solvent that lifts the oil and doesn't leave a residue or affect the seals should work. It ain't brain rocketry.