Oil Fill Confusion, and a Mystery Item

[ACQ_112]

Greetings. First post, and glad to be here ;o)

I have a couple of questions as one who is new to the automotive A/C world...

To begin, I am trying to work out/verify the correct total oil fill volume for a system with Diesel Kiki/Zexel DKS-15BH compressor (mfr label: #509640-0164) which is currently installed in a 1990 Volvo 740.

According to a couple of sources (including Four Seasons), the complete system oil capacity is reportedly 6.7 - 6.8 ounces. Looking around, I also see that the compressor alone seems to require 150cc (approx 5.3 ounces) of oil in the mechanism itself.

Now the trouble begins: If the compressor actually and in fact does require 5.3 ounces of oil, all will be well overfilled; as the accumulator (reportedly) requires 3 ounces -- and the rest of the plumbing will (anecdotally) require another 3 ounces -- for a total system fill of 11.3 ounces (165+% overfill).

Can someone help "clear the air" on this? Is there a spec resource and/or a reliable standard for these things??? I don't mind a bit less in the way of cooling efficiency with an inadvertent system overfill; but I would hate to damage the compressor by slugging way too much oil around in the long term...

Finally, I have a mysterious item which seems to be a vestigial coupler of some sort, and has been weeping oil:

Coupler.jpg (131.82 KiB) Viewed 1313 times

Coupler2.jpg (13.9 KiB) Viewed 1313 times

For reference, this item is teed into the line which feeds the accumulator; and is positioned at the end of a u-bent section of tubing that is filled with system oil. What exactly is this coupler, and can it be removed along with the u-bent section (and the contained oil) without ill effects?

Thanks for all your help, and have a great day --

[JohnHere]

Has the system in this vehicle been converted from R-12 to R-134a? The reason I ask is that the oils for these refrigerants are different and can't be mixed. R-12 uses mineral oil, whereas R-134a uses PAG oil.

According to a couple of sources (including Four Seasons), the complete system oil capacity is reportedly 6.7 - 6.8 ounces. Looking around, I also see that the compressor alone seems to require 150cc (approx 5.3 ounces) of oil in the mechanism itself.

The total oil specification that I have for your vehicle—6.75 fluid ounces—essentially matches what you already found.

Now the trouble begins: If the compressor actually and in fact does require 5.3 ounces of oil, all will be well overfilled; as the accumulator (reportedly) requires 3 ounces -- and the rest of the plumbing will (anecdotally) require another 3 ounces -- for a total system fill of 11.3 ounces (165+% overfill).

Can someone help "clear the air" on this? Is there a spec resource and/or a reliable standard for these things??? I don't mind a bit less in the way of cooling efficiency with an inadvertent system overfill; but I would hate to damage the compressor by slugging way too much oil around in the long term...

If the entire system calls for 6.75 ounces of oil in total, then you certainly don't want to add more than that. If you're starting with a completely "dry" system, you could put all the oil in the compressor if it will fit. Alternatively, you can use the oil-balancing method—that is, add 1 ounce each into the condenser and evaporator, 1.75 ounces into the accumulator, and the balance of 3 ounces into the compressor. With either method, the refrigerant will carry the oil with it to ensure the compressor is properly lubricated.

The component in your photograph looks to be a low-side coupler and/or test port, but it's one that I'm not familiar with. Perhaps it's a European-spec-only testing and charging port for R-12. By its appearance, it looks like a metal dust cover would screw onto the threads. Did the car come with a dust cover in place? In any case, I would remove it and the metal line and just add a standard R-12 or R-134a test fitting (whichever refrigerant applies) directly into the tee.

[ACQ_112]

Thank you, JohnHere, for your thoughtful reply.

I'll likely have a few more brief questions, but one thing comes to mind right off: It seems as though the total system capacity for a given lubricant is based on the behavior of the lubricating oil in context with a particular liquid refrigerant.

Specifically, and if I understand this correctly, the lubricating oil is chosen for a given refrigerant based upon the miscibility of the two substances. Separation only occurs when the refrigerant fraction is in a gaseous state.

Using this reasoning, there really isn't any particular, set amount of lubricating oil for any particular component of the assembled system; just maximum fluid/oil amounts which may be permitted to accumulate in any given component at one particular time. In operation, oil/refrigerant accumulation may vary at any point in the system within calculated limits.

Am I understanding this correctly?

Thanks again.

[bohica2xo]

Oil in the system is mostly transported along the surfaces of the components on the suction side.

Refrigeration compressors are gas compressors. What leaves the compressor is hot gas and oil mist. The condenser eventually reduces the refrigerant to liquid, and yes the oil needs to be miscible.

Once the refrigerant passes the expansion device the oil is on the surface of the evaporator. The velocity of the gas drags it along to the suction line and back to the compressor.

So there is a calculated amount of oil trapped in every component at shutdown. Dessicant beads are coated. there is a film of oil on the inside of everything. Most compressors maintain a quantity of oil in the area of the swash plate or crankshaft. Older compressors like the A6 or the Tecumseh have a large quantity of oil in the crankcase sump. The oil circulating in those systems was just what made it past the piston rings.

Newer compressors circulate more oil, and as it is drawn in on the suction side some is separated and ends up in the case sump. More like a 2 stroke engine migrates oil.

Oil circulation rates vary by vehicle, compressor model, and operating parameters. A lot of work went in to deciding the OCR for a specific vehicle.

[ACQ_112]

Thank you, bohica2xo, for this clarification. I think I have an idea of what's going on now.

The quoted 150cc "oil capacity" spec for this compressor is a nominal figure; the maximum installation volume from dry for the unit. And, those capacity figures which are often quoted for items such as accumulators are also nominal maximum installation volumes from dry.

Overarching in all cases, the nominal system fill specification should be considered optimal for the installation -- and should not be exceeded in total by much at all.

A little confusing to the uninitiated, but understandable enough in context...

***

Now here's another part of the puzzle which I am working through.

The vehicle in question has, for all intent and purposes, been in continuous storage for 15+ years. It's one of those rare specimens with very low mileage which was kept by an elderly man until his passing many years ago.

Based upon what is known, the A/C system on this car has never been serviced; and is thought to have stopped running over 15 years ago due to slow refrigerant leakage. Not uncommon, I presume, for older stored vehicles of this kind.

Along with the R12 went all of the compressor's sump oil over a generation or so; evidently seeping out until essentially gone. A small amount of R12 was found to be remaining in the system until just over 2 months ago -- which was cleared out in preparation for the servicing that I am doing now. I will not be converting the system to R134a.

Recent endoscope evaluation of the compressor internals during gentle manual rotation reveals no signs of evident wear; and the trace of lubricant (less 10cc) vacuumed from the bottom of the compressor shell was clean, light-amber mineral oil. The unit was never run without oil -- it all seems to have just seeped away over the decades.

Should I consider the condenser and evaporator to have a knowable amount of oil present? After all, barring an actual puncture, these items are configured to trap any system oil in solder-sealed containment.

In consideration of this particular situation, would it therefore be good practice to simply deduct the approximate oil volume which should be retained in the condenser and evaporator from the total system volume specification -- and add that difference to the evidently dry compressor (up to 150cc total in the unit) and into a new (or emptied) accumulator?

Thank you so much again --

[JohnHere]

Oh, I didn't know about this vehicle's history of sitting for more than 15 years. In this case, I would solvent-flush the entire system—including the hoses, lines, condenser, and evaporator—and proceed from there. Note that hoses and lines with inline mufflers (can-like devices) can't be flushed and must be replaced. The TXV, which you'll have to remove anyway to flush the evaporator, should be closely examined for any corrosion and/or defects and replaced if necessary. I would also replace the compressor since the front seal is probably shot, along with all the o-rings and seals. Then, add the correct amount of mineral oil to the system, evacuate well, and proceed to recharge it with R-12.

[ACQ_112]

Oh, I didn't know about this vehicle's history of sitting for more than 15 years. In this case, I would solvent-flush the entire system—including the hoses, lines, condenser, and evaporator—and proceed from there. Note that hoses and lines with inline mufflers (can-like devices) can't be flushed and must be replaced. The TXV, which you'll have to remove anyway to flush the evaporator, should be closely examined for any corrosion and/or defects and replaced if necessary. I would also replace the compressor since the front seal is probably shot, along with all the o-rings and seals. Then, add the correct amount of mineral oil to the system, evacuate well, and proceed to recharge it with R-12.

Despite the clean physical condition of the entire system with a decade + long leakout curve, a clear extracted mineral oil sample, and a compressor which resembles a new unit inside, everything must be either discarded or overhauled?

I don't understand what would compel this approach(?)

Please advise, and thank you again.

[tbirdtbird]

The comp shaft seal is dried up, along with the o-rings.
The reason you should turn your AC on occasionally in the winter is to maintain some oil on the shaft seal so that it doesn't dry up.
The other consultants on here are true masters of what they do and you will not find better advice anywhere else. Suggest you take that into account.

[Tim]

The other consultants on here are true masters of what they do and you will not find better advice anywhere else. Suggest you take that into account.

I found the option to assign a member status.

[ACQ_112]

The other consultants on here are true masters of what they do and you will not find better advice anywhere else. Suggest you take that into account.

Good to know where I am, and what my place is.

Moderators: Please close my account.

Thank you.