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right now I have a slow leak under vacuum in my AC system
Has any one had any success or tried pressurizing and then leak checking their AC system by either
1) nitrogen bottle with a regulator
2)just plain old air from a compressor
...then using soapy water at the various couplings? Since the system is under pressure when operating , seals and leaks can behave differently than they would under vacuum.
lots various YOUTube DIYs but none 928 specific....but they work
does it matter what port you introduce the pressure ? low or high....or both..
i understand that moisture may be introduce via compressed air but It’s pretty damn dry out here in the desert and the system will be drawn down extensively before recharging anyway.
I would assume you would add pressure similar to what the compressor would make with a proper charge at the associated port.? Or can you just add 50 psi and be done and go look for leaks .
i just rebuilt my compressor after what appeared to be a leaking shaft seal. I’ve added an appropriate amount ester oil with dye and have 4 cans of R12 standing by....so if push comes to shove, and for a waste of 100 bucks I could charge it with the R12 I have and go on a “dye hunt” if I had to.
Two options, spend about $200 to get a small N2 bottle and a N2-specific regulator at your local Airgas store, plus adapters to allow connecting your R12 AC gauges, then you can pressurize to ~100 psi and check for leaks with dishsoap brushed onto each joint. Or, you can spend $150 for a leak detector, and charge the system with a bit of R12 (or r134a if you've converted), and sniff each joint. The sniffer is more way more sensitive. William and I went down the path of trying pressurized N2 to figure out a leak in Minerva, but ended up sacrificing a bit of r12 to find the leak. The sniffer I bought is a Robinair TIFXP-1A Automatic Halogen Leak Detector.
If you want to do the nitrogen testing, here's the setup I put together.
I think you're looking at a working pressure of 250psi in the high pressure side. I imagine the proving pressure is even more. I don't say this lightly - but I'd leave that to the professionals.
Also, if you fill it with soapy water, how are you going to get it out? Moisture is the death of AC systems.
Just been down the same path early this year- unfortunately there is no easy "absolute" solution. What holds at 100 psig can easily leak when it sees 300 psig- simple mechanics tell us that and I found that to be the case. The system has two sections- high pressure from the compressor to the expansion valve and low pressure from the expansion valve back to the compressor suction port. To do a meaningful pressure test you need to hit 300 psig on the high pressure side. I have no idea whether these systems are designed to take full pressure on the low pressure side- I would think they are- but getting the system pressurised to this level is no joke either. Not difficult to see why the professionals use a sniffer with the system operational.
A system vacuum test tells us something but not everything. You should be able to pull a deep vacuum and hold it for forever and a day and if this is not the case then you have a problem that needs addressing- just a question of where the leak emanates from- to do this effectively you need a "micron" gauge.
With a sniffer It would not take much system pressure to detect a significant leak but the real problem lies with very minor leaks wherein it can takes weeks or months to notice the degradation as fugitive molecules take their path to freedom. Using a sniffer at pressures lower than normal operating might conceivably create a "false positive" but those who use such should be able to advise you better. In your case it might be prudent to pull the compressor and take it to an a/c shop- ask them to test it for leaks. If there are signs of compressor oil on or around the body it is a no brainer.
In my case the problem was the compressor seals both static and dynamic. I found a good a/c system shop and after they resealed the compressor my system then held vacuum. I also changed out all the seals to those suitable for R134. The hoses had been changed out earlier and I was under the impression that the static seals had as well but that was not the case or so it seemed but despite what we read it seems they held tight.
Finally folks are often cautioned about using moist air in the system and whereas this is not a good thing I am far from convinced it is an issue. The water vapour will disappear as the system is evacuated and for the few molecules that might be left the deliquescent material in the drier will absorb those remaining molecules- if they did not why would anyone fit them? Dry desert air in your location just not an issue
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I use nitrogen and pressurize it to 150-200 and have a spray bottle of soapy Dawn soap/water. Spray each and everything looking for bubbles. The only spot that is hard to test is the front compressor seal, but if you take the clutch off you can get to it.
I just went through the “rebuilding my compressor thing”. Rebuild went great but it still leaked at the shaft seal as the dye revealed. Got a new Denso from Roger and all was good.
Couple of more pics... The joints at the base of the three copper tubes all "glow".
My guess is that this is totally repair able... Just need to located a good AC repair shop here. Shouldn't be too hard... And now in the fall they shouldn't be too busy.
Anyone else run across a similar failure and course of action.... Thoughts... Thanks...
At this point I am just going to start removing the the interior anyway... Car is due for paint eventually... And I have half Of the crap out Of the back already.. 😂 😂.
I used 50 psi of air...and when I went inside the car to the rear AC, at the glowing joints, I could hear it hissing and escaping from the bottom of the expansion valve.
The expansion valve is a common failure point but it would be somewhat surprising to have several other failures concurrently. Whether or not such can be repaired effectively should be interesting
If it's helpful in deciding whether of not to keep the rear a/c, you can still get all the replacement lines, components, etc.
I just got a bunch of a/c lines from Porsche, backordered from Germany, some even had the original stickers with '85/'86 manufacture date. Good used front and rear evaporators from Mark.
My plan is to install Greg's condenser setup in the front right fender, I've read it helps with the dual a/c system. If I can make it to Shartoberfest, Kyle said he would make up some custom a/c lines since I'm blending +'87 parts to '85 parts.
Personally I'd like to have rear a/c in my S4, especially in the dead of summer here.
In industrial situations, the copper-tube heat exchangers get disassembled, cleaned and repaired regularly. Use silver solder. It's a Good Idea to stress-relieve the whole repaired assembly in an over after the repair is done. Then re-test for leakage before you install again.
The copper work-hardens with vibration in service, and cracks are not uncommon.
That said, it may be cheaper to get a good used unit from 928 International rather than chance on a repair. A good industrial HVAC shop will do you well if you decide to go the repair route. With all those hotels and their 40º water exchangers in the rooms, this is likely a pretty big industry in Las Vegas.
I posted on another thread also but it appears the problem IS the expansion valve Orings, (that is where the hissing was under pressure earlier)..and not the actual core.
not sure what the other material was that was on the copper joints but it glowed and when I Cleaned it with a pick , large chunks and flakes came off. Who knows what may have been spilled down there over 32 years, hardened and has now been covered in residual oil vapor.
inhave the rear core under vacuum now and its holding fine...
At least your core is still good! The o-rings and expansion valves do fail, but they are cheap and available fortunately. Coat your new ones in Nylog, that stuff is amazing.
I personally went with a rebuilt Denso (only get ones rebuilt by Denso) because of the possibility of the shaft having wear and chewing up the new seal.
You can put a few ounces of R134 in the system and use a sniffer to find the leak, pull a vacuum and then charge with R12. It won't hurt anything so long as you don't turn on the system.
The refrigerants aren't miscible with the oils each uses respectively.
10-14-2019, 02:33 AM
Pressure testing AC system for leaks.
