A/C leak...HEAD SCRATCHER...HELP!!!

[SyberTiger]

UPDATE on 11-08-2018: Scroll down for the solution

I've had a leak in several places on the compressor manifold hose assembly. This is the assembly that has the high pressure line running from the compressor to the condenser and the suction line running from the accumulator/dryer to the compressor. This was evidence by the appearance of PAG oil on and around the hose assembly. Since I needed to replace the hose assembly I decided I'd replace the compressor, accumulator and orifice tube too.

The compressor removal/install was a real PITA but got it back in and all the other new components in. But before I reconnected the wiring harnesses, the belt and buttoning everything else up I decide to put the vacuum on the system. Sadly, I have a leak somewhere in the system and don't have a clue as to where it's leaking vacuum. It takes about 10 minutes for the vacuum to draw down.

I didn't want to put dye into the system just yet or attempt to recharge it by running the engine. I picked up an electronic leak sniffer from Harbor Freight in hope of it helping me find the leak. Without running the compressor I was able to put 1/2 can of R134a into the system. I wasn't able to find a leak with the sniffer. The instructions say that you need 50+ PSI to detect a leak. I noted that the 1/2 can got the pressure up to 72 degrees which I assume is also the ambient air temperature. Oddly, with the system is holding the R134a steady without leaking out after an hour. Does this mean that R134a molecules are larger than air/atmosphere and the leak is small enough where it will not escape?

No obvious signs of leaks or PAG oil anywhere else in the system including the condenser....obviously, can't see the evaporator and I should say I've never smelled R134a/PAG in the cab.

Any suggestions? I seems weird to charge up (with dye) the system with the compressor running knowing I have such a large leak. Clearly I'd be sucking in air or certainly there'd be air in the system since it cannot hold vacumm. I never was big fan of using dye mostly because that chit seems to get everywhere.

 

[shucker1]

In theory when you have vacuum applied your pulling all of the connections inward toward each other.

With pressure applied you forcing them apart and jamming the leak source shut?

When you did your test did you recall outside air temp? I think you said 72 Degrees?

Tomorrow if the outside temp is the same recheck your pressure. It should be close to the same. + or - a PSI or two.

If you can get past that stage I would feel good putting Freon in.

You may have had a weak connection between you vacuum pump and gauge set.

I've got an old homemade unit.

A working compressor out of a freezer with fittings soldered on.

 

[SyberTiger]

You may have had a weak connection between you vacuum pump and gauge set.

.

I should have mentioned that I checked the integrity of the connection between the red and blue lines to/from the manifold gauges...they hold vacuum so the leak is definitely in my vehicle's A/C system.

 

[shucker1]

Copy that.

How long did you draw vacuum?

I usually draw for at least 45 minutes before I test.

 

[SyberTiger]

Copy that.

How long did you draw vacuum?

I usually draw for at least 45 minutes before I test.

About 10 minutes as I was only doing a cursory test of the system. Usually, I like to run it for at least an hour maybe longer.

 

[shucker1]

Gotcha.

We both agree I guess.

You may have had some residual moisture trying to evaporate the raised you vacuum set point.

 

[lincolnshibuya]

you are better off using a dye instead of that electronic leak sniffer from Harbor Freight (used that before and it's not working well, luckily returns are no questions asked in Harbor Freight) I usually buy PAG oil with dye in my compressor. A shot of those $12 bottle dye/UV leak detector also works well. Use brake parts cleaner clean it off. There's a $20 kit that includes the mini flashlight and glasses for the UV dye detector. Best time to check it out is when you're inside the garage or when it's dark outside.

 

[SyberTiger]

It's been 11 months so I thought I'd give an update and hopefully this is the end of this thread as far as I'm concerned because the leak issue has been resolved. It's not a big deal but the reason I wanted to report my findings is just in case someone else is experiencing a leak and can't find it either.

I ended up putting dye into the system back then charging the system as best I could. I "free" rented the UV leak detect kit (UV light and goggles) from AutoZone back in January and decided I'd just run the system as normal and check every now and then to find the leak. Can you believe it, having checked every month using the UV light and special glasses I never could find the leak. And, I tried...I tried hard, climbing all over and under that vehicle including inside the cab. I finally returned the "free" rental last month after having borrowed if for 9 months. Turned out that exercise didn't reveal anything. I noted about two months ago the AC started to cycle as if getting low on refrigerant so it was obviously leaking but slowly.

Anyhow, I just decided that since I had not replaced the condenser that surely this must be the problem so I ordered one and just installed it. When I pulled out the old condenser I noted that there were no signs of leakage, zip, zero, zilch. When I installed the new condenser I noted that on the high pressure side connection it looked to me like the O-ring that had been installed was kind of small. Comparing it to the low pressure connection O-ring it was in fact small so I put a larger one to match the low pressure side. I added 1oz more of PAG oil to accumulator to adjust since no doubt some oil was still inside the old condenser that was removed. I also put in another orifice tube to replace the one I installed at the beginning of this project. Then the big test to see if it would hold a vacuum... YES! Yes, it was holding vacuum whereas before it would take about a couple of minutes for all the vacuum to dissipate.

In the end I still don't have a clue if the leak was in the old condenser or around the high pressure connection. There was no oil residue from a leak and there was no detection of UV dye. So strange. The only thing I can think of is that the leak was so small that the air/refrigerant molecules being smaller could leak out but the the PAG that had UV dye in it. How else to explain it?

Anyhow, I hope my findings are comforting for anyone with a leak problem because it can be so frustrating when both an electronic sniffer and the UV dye system don't work.