AC leak detection

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Mar 27, 2003
Groveland MA
I've had no AC for a few years now. I started by adding dye and found what I thought was a leak 8in the condenser so I replaced that. I had a friend come over and it seemed to hold vacuum so I charged the system and it held for a few weeks and went dead.

this year I pulled the evaporator and found yet another spot so I replaced that and bought a gauge set and vacuum pump and pulled vacuum on the system. I let the gauge sit for about 30 minutes with the pump off and it held vacuum so I filled the system. This time it lasted on a few days.

I'm obviously at a loss with this. I thought if the system could hold vacuum it was considered sealed. I've read where people pressurize their systems and then spray them down to find leaks.

Is this the best way to find leaks? And how would I go about do this?
Did you check the L and H valves on the Compressor? They could be leaking. Your vacuum test would not detect this. They can be tightened like a tire valve. You can use some spit in your finger to see if either of them creates a bubble. Whenever I add freon, I take a screwdrive and press the valve and let a small amount of freon out and let is snap closed. I think this ensures a good tight seal.
As John has said, the valves on the service ports are always suspect. I change them just for good measure. And as he said, they are exactly like bike tire valves, and I'm sure all of us have had a flat on a bike when there wasn't a hole in the tube. Another thing that might be occurring is the front seal for the shaft may only leak when the compressor is turned on, or when the shaft is resting in a certain position. You should be able to see the dye being slung if that was the case though.

My favorite way to find leaks is to put air into the system and spray soapy water on every component. If you see a bubble, there's a leak. However, I have seen countless service port valves leak, but some only at a certain pressure. Again, just like a bike tire, ever had a half a flat? The fluctuation in pressure at any given time may allow the valve to leak, then at others there is no leak.

Make sure you check/change both high side valves, I think there are two, there are on the 94 anyway.
Soapy water on a pressurized system has always worked great for me. Kinda messy, but spray on little and if there is a leak the bubbles will let you know. Put about a can of R134a in it for pressure. You may have the shaft seal leaking on the compressor... especially if it has sat around unpressurized for a long time.

Also how much of a vacuum are you pulling. Try to get as good of vacuum as you can. The better the vacuum, the tighter the system needs to be to hold it. The higher vacuum also helps to "boil" out any water vapor inside the system, so your receiver dryer will work better.:cheers:
I've changed out the schrader valves already on the service ports but did notice another one on the high side line the other day.

To check the shaft seal do I need to remove the clutch?

I'm vacuuming the system down to were it pegs the needle on the gauge below -1 bar.
-1 bar = -14.xx psi. That's not good on my vacuum radar, but your vacuum pump may be weak, or your gauge inadequate. Change out the additional high side schrader valve. The shaft seal leak should be evident if dye was introduced into the system. You should be able to see the fluorescent yellow with out goggles or a black light. The oil being slung around the nose of the compressor is the tell all. However, an untrained eye could miss this. Is there a black oily residue that has built up between the front of the compressor body and the clutch? It may now be a greenish black color due to the dye.

Did you put some oil on the o-rings before you connected the lines together after you replaced the evaporator and condenser?
Hi Rick,
When you apply vacuum to the system, it pulls the fittings and seals together and can hide the leak. Under pressure, the fittings and seals are pushed apart, possibly allowing a leak. Robinair makes really good equipment, so hopefully, your vacuum pump will pull about 29" +/-. It takes about 45 minutes to remove all the air from the system. On your compressor, no need to remove the entire clutch, you just need to pull the front hub off. I think it uses a 10mm socket and a 1/4" impact will take the bolt out and the hub will just pull off. Be sure to watch for any shims (there may be more than one) that may stick inside the hub-they will need to go back in place when re-installing the hub. With the hub off, you can use a dye light to see if there is evidence of a leak at the shaft seal. The compressor manifold gasket(pic below) is a known leak problem-but you should see dye around the edges if it's leaking.
I hope this helps,

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