High side AC leak

[JHZR2]

I don’t know how long ago the AC was run in my auction win 1991 MB 350sd. Likely years. Put gauges on it, and the pressure was about 7-8 psig.

The high side connector is caked with dirt, which tells me there probably was a slow leak at the 134a adapter.

I would likely revert the car back to r-12 once I know it’s leak tight. Until then, I’m inclined to refill with r-134a, though if I have a suspected leak, I usually use HC with great success.

Given that it is likely years and the car still had a bit of charge, in cold weather, and I have no evidence that there was any barrier hose replacement, what path would you take? I’m thinking to carefully add r-134a to an acceptable pressure and running it for a while, sniffing and watching pressures. Assuming that holds, I can then either have it evacuated and refilled by weight, or more likely, evacuated, then I’ll flush it, change the R/D, and instal r-12 which I have, by weight. Obviously installing r-12 without significant confidence in the system (which I do in other cars that still run r-12).

Thoughts on the grime around the high pressure port? Thinking I should change orings and schrader in advance. What about the r-134a plan?

Thanks!

 

[paulo57509]

I would be weary of the condition of the system; is it just a leak or is there additional work to be done to get it running? At a minumum, I would draw a vacuum (how gross are the leaks), if the leaks are "slow", partially fill the system and sniff them out. Once this assessment is complete, you can then make more informed decisions on how to proceed. I wouldn't convert it until I know the system is sound.

IMO, with AC work there are no shortcuts. Even patching it back together can get expensive really quickly; time and money are better spent just repairing the system properly.

I converted the Lumina to R134a back in 2011 when the system succumbed to "black death" compressor failure. This required removing all the components, flushing the system (lacquer thinner) to remove the mineral oil, black debris and replacing the seals, compressor, orifice tube, receiver/dryer and hoses at the compressor. The Lumina is now falling apart and really needs to be junked. The AC however is still performing like new.

 

[JHZR2]

I would be weary of the condition of the system; is it just a leak or is there additional work to be done to get it running? At a minumum, I would draw a vacuum (how gross are the leaks), if the leaks are "slow", partially fill the system and sniff them out. Once this assessment is complete, you can then make more informed decisions on how to proceed. I wouldn't convert it until I know the system is sound.

IMO, with AC work there are no shortcuts. Even patching it back together can get expensive really quickly; time and money are better spent just repairing the system properly.

I converted the Lumina to R134a back in 2011 when the system succumbed to "black death" compressor failure. This required removing all the components, flushing the system (lacquer thinner) to remove the mineral oil, black debris and replacing the seals, compressor, orifice tube, receiver/dryer and hoses at the compressor. The Lumina is now falling apart and really needs to be junked. The AC however is still performing like new.

Im acutely aware of the situation with old ac systems. I maintain R-12 systems on many old cars. I’ve had to rebuild and change systems before.

R-12 is the best bet for cars meant for it by design. I’ve had decent r134 retrofits but there are many variables.

Right now im just baselining this new to me vehicle so I can see how it performs and make decisions for the long term. Frankly, seeing that much pressure, while leaking slowly, tells me that the system isn’t that bad. I can’t vent the remaining r134, and I don’t have bone dry nitrogen. But I do need to do diagnosis, and I have no way to tell how slow or fast any leak is. But I suspect it’s very slow based upon the cars history. So it’s really a matter of $9 in HC or $13 in r134a.

 

[Fitter30]

R 12 system uses mineral oil R134a uses polyolester oil (POE). Using nitrogen would be the best choice after repairs for leaks. It's doesn't change pressure with temperature that much. Before and after a evac with a micron gage just to remove any refrigerant that might have migrated into the oil. Might want to replace the expansion devise and drier also after the leaks are repaired.

 

[JHZR2]

R 12 system uses mineral oil R134a uses polyolester oil (POE). Using nitrogen would be the best choice after repairs for leaks. It's doesn't change pressure with temperature that much. Before and after a evac with a micron gage just to remove any refrigerant that might have migrated into the oil. Might want to replace the expansion devise and drier also after the leaks are repaired.

Yes, I’m aware of the oil differences. Keep in mind I’m not yet doing an R-12 convert-back. That would require a decent disassembly of the system, flushing, etc.

Definitely in the cards.

For now, I’m just baselining the car and making it useful as part of my collection. That means understanding the AC system status, and what is or isn’t good with it. Evaporator is my biggest fear, but it seems that since the system still had marginal pressure, that the evaporator isn’t leaking.

Beyond that, it’s a matter of having a working ac so I can start to use the car a bit.

 

[JHZR2]

I’m investigating this more. I had no idea the amount of time since the system had been charged. Remember that I bought this car at auction.

I undercharged the system a bit purposely since I needed to diagnose, and didnt want to waste r-134a. On other cars that I intend to keep r-12, I’ve done my leak investigations with envirosafe HC refrigerant first since that can be vented.

This car had 134a ports (not that this means a lot), and cooled well on a slight charge. We ran it like that to the Manteno HPL event, and it was doing wel until recently.
OK so it’s not a super slow leak…. It’s slow, but not appropriate. So I got out my sniffer. I can sniff refrigerant at both ports, noplace else. This was surprising to me since I know it’s weeping oil from the receiver dryer.

OK, easy enough to replace the ports. Since I’m replacing the sensor, might as well do receiver drier at the same time then since I don’t want moisture.

I had the remnant r-134a evacuated locally. Then I went to work.

Pulled the existing retrofit ports. The old R-12 schraders were removed. Good.

I cleaned everything and replaced any o-rings up front there just in case. They were pretty flat and black.

Used Nylog blue on everything. Used new service ports with new green o-rings.

Had to use new orings in the sensor holes. The ones that came with the R/D, which was from Taiwan not Germany (Rein brand) weren’t the right size.

The R/D got about 2oz of POE oil with dye and everything got closed up.

Pulled a long hard vacuum on everything and it held fine.

OK, so here’s the odd thing. With that hard vacuum I attached a partial can of 134a that I had. It took the pressure from negative to about 20psi. Obviously there’s no liquid in the system.

I didn’t have to jumper the switch to get the compressor to start. It pulled down the rest of the van easily. And it pulled down to near zero which I’d generally expect. But the weird thing is that the compressor didn’t cut out on this happening. It just kept running. You could see refrigerant flowing in the sightglass. So things were happening.

But shouldn’t the compressor have cut out? Because it didnt, what does that indicate? The high side obviously wasn’t very high, like 50 or 80, and there was sound from the expansion valve, minimal discernible cooling. Again, all expected since it had maybe 8-10 oz in there. But why isn’t the compressor cutting off? That concerns me. I don’t want to go too far with it like this in case I need to replace something else…. Thoughts????

 

[mk378]

The low pressure switch is on the high side. Once there is enough to start the compressor, the high side pressure stays up and it will keep going. Don't keep running severely undercharged. It doesn't need to be running to sniff for leaks.

These systems cycle off on evaporator temperature.

 

[JHZR2]

The low pressure switch is on the high side. Once there is enough to start the compressor, the high side pressure stays up and it will keep going. Don't keep running severely undercharged. It doesn't need to be running to sniff for leaks.

These systems cycle off on evaporator temperature.

I’ve put about 22 ounces in now, it’s blowing cool to cold in the horrendous humidity we have.

The thing that concerns me a bit, maybe since it’s been so long since I’ve run a 134a retrofit, is that the R/D seems to have too much of a foam in the sightglass. I’m used to seeing bubbles but this is more like a million tiny bubbles or foam.

I did put POE oil into the RD. Maybe it’s related? I don’t know. Maybe after the system shuts down and settles a bit it will be more normal.

But it just seems odd…

Everything passes the sniff test. Pressures are ok per the charts for 80s and very humid. This was just a photo I took while charging before it was blowing cold.

This was at idle, bad fan clutch, blowing cool not yet cold. I wasn’t ready to fine tune it and I know I’m around 50% of the r-12 mass. So I’m fine. I’ll fine tune it with a box fan and helper holding RPMs up a bit, and a good fan clutch. I did verify that the aux electric fans worked and cycled, which would take pressures quickly to 25/150ish.

I won’t be upset if I don’t make these high side pressures and the system isn’t as absolute cold as it could be. I recall the R-12 high low pressures are lower though I can’t seem to find a chart like this anymore!!

 

[JHZR2]

I added a few more ounces. The operating pressures didn’t change, so that’s good, means it’s really just filling the receiver dryer with liquid I believe. Installed a new fan clutch and it seems to keep the pressures lower so that’s good. Air is blowing nice and cold.

But I’m still seeing foam in the sight glass. I expect with 134a in an r-12 retrofit to see bubbles, but this is tiny foam.

Any ideas? I don’t want to kill my compressor.

 

[CDX825]

Only thing I could think that would cause foam is non condensables in the system.

 

[JHZR2]

Only thing I could think that would cause foam is non condensables in the system.

You mean air?

Definitely none there. I purged the fill line and filled into a hard vacuum.

I did add POE oil. One thing I read in one place is that while it’s compatible, it isn’t miscible with 134a. So it can transport around but will look foamy in a sight glass. 134a systems can have bubbles regardless so this makes it worse. I don’t know. Just one theory….

Viewing a thread - R/D sight glass for R134A

talk.newagtalk.com

What I got from a couple of AC retrofit sites that were heavily into so many conversions, said this. They said that synthetic ester oil in R134a, never blends with the refrigerant, it moves through the system as globs of clear oil, looking exactly like bubbles, so you will never have a clear sight glass with that oil and refrigerant combo. They said to ignore the sight glass, as you can be seriously overcharged and still have what appears to be bubbles. In reality it is globs of oil that is rushing past the sight glass.

The system is running beautifully for 80 and humid. Have to turn it down actually.

 

[CDX825]

You mean air?

Definitely none there. I purged the fill line and filled into a hard vacuum.

Yes. I see you pulled a vacuum and let the system sit to see if it held. I am not crazy about this method of leak testing but I see it done a lot. Reason being is that without a micron gauge you really don't know if the system is leaking or not. A regular manifold gauge set isn't really sensitive enough on the vacuum side to show it. A small leak can allow air back into the system and it would never show on the manifold gauge set. Not saying that is the issue for sure but that was something that crossed my mind.

 

[Powerglide56]

That’s a lot of green. Looks over oiled to my eyes.

 

[JHZR2]

That’s a lot of green. Looks over oiled to my eyes.

Perhaps. I added a bit under 2oz per the FSM. It blows nice and cold. Wouldn’t over oiling impede performance?

Yes. I see you pulled a vacuum and let the system sit to see if it held. I am not crazy about this method of leak testing but I see it done a lot. Reason being is that without a micron gauge you really don't know if the system is leaking or not. A regular manifold gauge set isn't really sensitive enough on the vacuum side to show it. A small leak can allow air back into the system and it would never show on the manifold gauge set. Not saying that is the issue for sure but that was something that crossed my mind.

That’s fair. That’s why usually I troubleshoot with HC blend so I can sniff for leaks. This time I went straight for 134a since I’ve never sniffed a leak with my detector while under pressure.

If air really came in under a hard vacuum, the quantity of air in there is minuscule. It wouldn’t blow cold if there was any real amount of air, right??

 

[Chris142]

Ignore the sight glass when using r134a. If you fill it till they are gone it will be overcharged

 

[demarpaint]

Perhaps. I added a bit under 2oz per the FSM. It blows nice and cold. Wouldn’t over oiling impede performance?

Yes over oiling can impede performance. The oil takes the place of refrigerant. The wild card in adding oil is you really have no idea how much oil is in the receiver drier, evaporator, compressor, hoses, etc. unless you're starting from scratch. But if it's blowing cold don't sweat it.

 

[Fitter30]

R134 charge is 80% of the R12 charge by weight. Was the expansion devise replaced when the system was converted?

 

[JHZR2]

R134 charge is 80% of the R12 charge by weight. Was the expansion devise replaced when the system was converted?

No idea. This is a car that I won at auction last September and didn’t have details that I’ve found yet on what had been done. The compressor looks original or at least it has been on there a long time.

IIRC the expansion valves that MB sells as replacements are rated for r-12 and 134a, there aren’t unique parts.

I’m not yet at 80% by weight but it is blowing very cold and handling 90+ ambient and high humidity in dc traffic with ease.

 

[JHZR2]

Ignore the sight glass when using r134a. If you fill it till they are gone it will be overcharged

That has been my understanding. In fact, the R/D came with a black sticker over the sight glass!

I’m not opposed to seeing bubbles, I understand it’s expected for 134a. I’m more concerned about the foamy/tiny bubbles versus larger ones that I’m used to seeing.

Yes over oiling can impede performance. The oil takes the place of refrigerant. The wild card in adding oil is you really have no idea how much oil is in the receiver drier, evaporator, compressor, hoses, etc. unless you're starting from scratch. But if it's blowing cold don't sweat it.

Exactly.

Ultimately I’m inclined to take it back to R-12. That’s just not in the cards right away, and it’s hot and in the summer, and I want to use the car. Since I know the system is tight other than those adapters (which now don’t leak and I run gasket caps with a touch of nylog) or should be tight….

It was a wild card how much oil to put in, the FSM says to distribute about half the oil between the evaporator, condenser, and r/d. So that’s what I put in. It can’t be overly oiled by more than a teaspoon or two.

 

[Fitter30]

Don't even look at the sight glass with 134a. Especially with a converted system.

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