Which oil in AC compressor? - PeachParts Mercedes-Benz Forum

tyl604 · #1 02-06-2019, 09:17 AM

Bought a new R4 compressor for my '81 300SD. How do I know whether my existing lines have Pao oil or mineral oil? Smell, taste? What?

Diseasel300 · #2 02-06-2019, 09:52 AM

If you were running R12, you'll be mineral oil. If R134a it can be PAG, POE, or PAO. When replacing the compressor, you should be flushing the lines and replacing the receiver/drier anyway, so it should be a moot point.

tyl604 · #3 02-06-2019, 11:06 AM

Diseasel300 - thanks for sticking with me. How do I flush the lines? Mineral oil from Walgreens or is it something special?

Diseasel300 · #4 02-06-2019, 11:22 AM

Search the forums or online for a DIY guide. Flushing the lines typically involves a flushing kit, some cleaning solution, and compressed air to flush out any debris and old oil.

The mineral oil for R12 is specific for refrigerant, it is unlikely you can buy it at a local store, you'll probably have to order it. The FSM has specific amounts and places to add oil when rebuilding the system since the R4 doesn't have a normal sump.

If you're not 100% certain what you're doing, it's a very good idea to farm the job out to someone with the equipment and experience to do the job right. Since you'll have the system open to flush it, it's a good time to replace all the O-rings at the same time. Do it right, do it once.

tyl604 · #5 02-06-2019, 12:37 PM

Thanks for the help. I learned about R12 mineral oil; bought a quart at Advance Auto for $10. So now I know what that is.

About 10-15 years ago when I replaced the original compressor, I just got an indy to add the oil and freon. When I looked around several months ago, no one wanted to mess with Freon.

Will have to keep checking.

Was surprised that the mineral oil did not have dye in it; could not find the oil with the dye.

So I am beginning a journey.

tyl604 · #6 02-06-2019, 01:58 PM

Ok. Youtube video says (if you do not flush oil out of system) empty and measure oil from old compressor. Empty new compressor. Add only the amount of oil that came out of old compressor. Otherwise you put too much oil in the system.

Of course if you flush system you should add back (I think) 8oz of mineral oil.

Diseasel300 · #7 02-06-2019, 02:59 PM

If the old compressor grenaded or wore out, the system needs to be flushed. Otherwise you'll ruin your new compressor in very short time. The R4 does not have an oil sump, it should contain very little oil, most of the rest will be stored in the receiver/drier and in the various hoses and coils. You shouldn't even consider opening the system if you're not prepared to flush and replace O-rings and receiver/drier. You're just asking for trouble. Oil without dye is highly preferable to the kind with dye. The dye is useful for finding leaks, but it can interfere with operation of the expansion valve over time.

tyl604 · #8 02-06-2019, 03:42 PM

Got it. The compressor did not grenade; the shaft started screeching. I had to cut the belt.

I have asked Pep Boys if they can pressurize the system to check for leaks without using my four cans of R12. They said can do. However the fellow I talked to could not tell me what they would use. Cannot be R134a or something that would pollute system. Cannot be R12; too expensive and they do not have any (cannot use mine). I am thinking nitrogen but could not find anyone at Pep Boys to confirm. Guess that's a problem for later.

Diseasel300 · #9 02-06-2019, 04:13 PM

Most A/C service places use nitrogen for pressure testing. If they'll do it, have PepBoys do the flush, pressure test, and evacuation, then you can recharge with R12 at home. Most A/C shops will perform a recovery/evacuation for a DIY to do the charging. It also releases them from liability using R12. Worth asking at least. If not, find a local independent shop, they'll probably be more communicative and flexible.

tyl604 · #10 02-06-2019, 04:51 PM

Wow; great info. But confused. If Pep Boys does a flush, pressure test, and evac - how do I get the oil back in? There is no oil in my R12 cans.

Here are the instructions for the R4 compressor:

Zulfiqar · #11 02-06-2019, 05:29 PM

To pressure test, hire a nitrogen tank from a gas supply store, they also rent the regulator. It will connect to your HVAC manifold.

To flush the lines, you will need to get some cleaning solution from NAPA or somewhere and a pressure can which is then used with compressed air. Flush the remaining out with pure methanol and nitrogen purge all lines. To add oil just add to different components as the R4 cannot hold any oil in itself.

On an R4 its best to charge the system completely with compressor off (requires large refrigerant tank) . But as you cannot do it because of small cans do it the regular way.

Zulfiqar · #12 02-06-2019, 05:32 PM

Quote:

Originally Posted by tyl604

Ok. Youtube video says (if you do not flush oil out of system) empty and measure oil from old compressor. Empty new compressor. Add only the amount of oil that came out of old compressor. Otherwise you put too much oil in the system.

Of course if you flush system you should add back (I think) 8oz of mineral oil.

Take that with a pinch of salt, not all compressors are the same, as mentioned the R4 has no oil reserve in itself. Its not just ancient compressors like the R4 either.

on the W210 etc. the variable compressor has a ton of oil in it (its a harrison V5 clone) - but a few drops only come out of the ports. the actual oil is held in its crankcase and has caused lots of grief to DIY people as they dont know they have to drain from the crankcase fill/drain bolt.

ah-kay · #13 02-06-2019, 05:50 PM

AC is very simple if you have the tools. If not then it is cheaper to seek help from professional. I do all my AC and I don't normally flush the system and it always come out OK. The amount of oil to add is difficult to measure unless it is a brand new system. Some oil, more oil is better than no oil.

tyl604 · #14 02-06-2019, 07:59 PM

The compressor did not grenade, the shaft started screeching. To date it has not been open to air but I did have a leak because over a period of about two years I lost all my freon R12.

Have been advised to flush. The manual for the new compressor says to flush.
Then it says to add half the oil to suction side and other half to "accumulator or low side of the system." So with a flush and no oil remaining, I think that would be 8 oz.

What the heck is the accumulator?

If I take the no-flush advice (the easy path), how do I know how much oil to add to the new compressor? Directions say it is " shipped with assembly lube or ICE 32; do not drain it, add the proper amount of oil to it."

Again - assume no-flush option, do I drain the old compressor, measure, and add same amount of new mineral oil to the new compressor - assuming remainder of 8 oz is in the lines? Add zero to the accumulator?

I know this seems like a simple problem but I am not sure what to do if I go with the no-flush advice. And not sure I am going that way yet.

Zulfiqar - thanks, that info helps. Had not thought of that.

tyl604 · #15 02-11-2019, 06:54 PM

Well, I am getting there. I have another thread called "81SD why replace drier" which should probably be combined with this thread. Here is the plan:

Replace compressor and not the drier, have pressure tested with nitrogen by indy to find leaks. If no leak, replace drier, add R12 mineral oil, and have vacuumed down by indy. Add R12. Not replacing the expansion valve under dash which is supposed to be quite hard.