Air conditioner leak detection

[Tbob]

A few years ago, I moved from Indiana, where A/C was helpful but not really necessary, to Florida, where A/C is much more important for comfort! Almost mandatory! So last year I replace all the hoses with barrier hose, the condenser with a parallel flow condenser, and a new compressor, receiver dryer, etc.. The system will hold vacuum overnight with no change, but when I fill it with R134a, it will leak down in a few days. I've not been able to find the leak, even with dye in the oil and a uv light, now my next step is to pressurize the system with some gas other than R134a. For diagnosis purposes the recommendation is nitrogen, and I could buy a nitrogen tank and set that up, but I was wondering if there would be any problem with using Oxygen. I have an oxygen tank on my welding rig, so I wonder if I could use that oxygen as a pressurized gas. I could check with the gas supply house to find out if welding oxygen has any moisture in it, and if not could it be used instead of Nitrogen? I know this is not the normal type of Vanagon question we normally see, but I know that a lot of you guys work with A/C quite a bit, so I thought I would ask.
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1969 Deluxe, owned since 1973
1973 Westfalia, owned since 1983
1980 Westfalia, watercooled conversion
1985 Westfalia, stock!
1986 Westfakia, Audi I-4 conversion
A couple of trucks and a couple of Jeeps

[MarkWard]

I see a lot of warnings regarding oxygen and sparks. I don’t think it’s flammable, but oxygen rich environments must catch fire more easily.

A leak that wouldn’t show up under a vacuum test but leak out in a couple days is a pretty good leak. What is the age of the compressor specifically the shaft seal. It’s pretty easy to remove the clutch cover plate and view the shaft area without discharging. The evaporator core is difficult to check for leaks visually. It’s sort of a process of elimination.

Years ago, we’d search for Freon leaks with a rig on a propane torch bottle. Certainly that was more dangerous introducing a flame into an engine compartment or interior. Electric sniffers came available and the propane testing went away. Too many false positives on the snifflers to be accurate. The UV die was a game changer. Good luck getting it sorted. It is a necessity in the SE this time of year.

[67rustavenger]

Oxygen is not a good idea for a detection gas.
If you could find a helium leak detector, that would be the ideal tool to pin point a leak in the system. Unfortunately Helium leak detectors are very expensive for a once in a while tool to find a coolant leak.

This might be a better solution for finding a leak in your system,
https://www.amazon.com/Refrigerant-Detector-Adjust...2c1df98776
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[jlrftype7]

Once refilled with Freon for testing, don't discount plain soapy water for finding leaks. Messier than the Leak Detectors while in Interior spaces , but it does work and can be applied in tight spots with a spray bottle.

Agree with Mark about the frustration of False Positives, or not finding the leak in the first place when using Electronic Leak Dectectors.
Some common Automotive fluids will set off many of the Leak Dectectors, like Washer Fluid, Brake Clean. I've even had carpet that was probably outgassing give a reading to a tester at times.

Good that you gave up using a Flame as a testing method, Mark ,,,,,years ago, Phosgene Gas is nothing to mess around with...

WW1 Vets would have told you some stories about being gassed with Phosgene Gas. Starting out as a Tech in the mid 80s, our Shop teachers stressed why not to use a Propane Flame as a testing method. Electric Testers were just coming into wider spread use back then. We regularly used a Corded Version that was fairly accurate, but having an extension cord to lug around the interior of a vehicle was a pain too....
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'69 Semi-Auto Stick Shift Beetle-gone
2017 MINI Coopers, our current DDs
‘84 Tin Top - Hilga....Auto

[fxr]

I had a similar situation, with everything changed out except the evaporator. Work fine for a few days, just about after two weeks, useless after three weeks.

I was using Envirosafe 134a substitute with a dye. Could I see any hint of dye? No.

I went to buy some more Envirosafe, and they now had cans with leak-stop in them. I know, I know, never use that in an A/C system, but as the next step would be a complete evaporator and expansion valve change-out, I thought - Why Not.

Just one can of this added to whatever was left in there without any bother with vacuum or flushing air out of hoses - pressure went up, it got cold, wait and see...

No leak discerned after four weeks. Win! For the moment at least.
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Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300

[skills@eurocarsplus]

I've never not had dye work, but in a system as big as a vanagon I'd expect 1) to use a lot of it and 2) it taking a few days to show up.

That said, vacuum testing is a poor metric seeing the system operated under pressure.

soapy water would work, but there is very low pressure in the evaporator, about 30-40 psi. just keep that in mind.

I've also had a rash of shitty Schrader valves too.
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[Tbob]

Thanks, guys, for the answers. I have an electronic leak detector, I bought some of that special soap that the hvac guys swear by, every leak detection method I could buy except the nitrogen. Dye in the system, uv light, everything I could think of. No leaks detectable, and filling it with R134a just to have it leak out is not good for the environment nor is it inexpensive. I think I'll go get a nitrogen bottle next week after the holiday.
_________________
1969 Deluxe, owned since 1973
1973 Westfalia, owned since 1983
1980 Westfalia, watercooled conversion
1985 Westfalia, stock!
1986 Westfakia, Audi I-4 conversion
A couple of trucks and a couple of Jeeps

[MarkWard]

You can use the leftover nitrogen for filling your tires are your fleet.