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loses vacuum but holds static pressure

masintenn on Thu April 03, 2014 10:56 AM User is offline

Year: 1998
Make: Toyota
Model: Camry
Engine Size: 2.2
Refrigerant Type: r134a

My Camry a/c stopped working over the winter and the compressor wouldn't cycle on. Gauges showed 0 static pressure and the system would lose vacuum in just a couple minutes. Added a 12oz can of 134 w/ dye and found the lines leaking massively at the compressor so I replaced the o-rings after paying to have the system evacuated.

Pulled a vacuum and it still wouldn't hold! Verified the gauges weren't the culprit and would hold vacuum when the connectors are closed. Replaced the o-rings again and it still wouldn't hold the vacuum, although it seemed to be losing it slower than before they were first replaced. Initially lost vacuum in ~2 minutes and now losing it in ~5.

So I added another can of 134 w/dye and can't find a leak anywhere under the hood. I left the gauges hooked up overnight and they had dropped a few psi due to temperature, but were still holding around 30psi.

So my question is what is going on that would cause the system to lose vacuum but hold static pressure??? Do I likely have a small leak at the evaporator or expansion valve in the cabin? What is confusing me is that it won't hold 30inHG vacuum will hold positive pressure. What am I missing?

Edited: Thu April 03, 2014 at 10:58 AM by masintenn

masintenn on Thu April 03, 2014 1:26 PM User is offline

I hadn't done any a/c work in several years, so I've now refreshed my knowledge and understand that the static pressure simply tells me that there is refrigerant in the system. The immediate loss of vacuum means that I've still got a leak that I need to track down.

mk378 on Thu April 03, 2014 4:34 PM User is offline

When you're using refrigerant for a static pressure test, you need to stay below the saturation pressure. Then all the refrigerant in the system will stay gas, and you will notice a pressure drop if any leaks out.

Dye only works to show leaks if it is circulating with the system fully charged and running. If you don't have an electronic leak detector, that would be a potetnial, though less preferable, way to find leaks.

With the lines under static pressure, you could also try soapy water on the outside of all the exposed connections and look for bubbles.

GM Tech on Fri April 04, 2014 10:10 AM User is offline

Worn out shaft seals will hold static, but not vacuum at times

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

masintenn on Fri April 04, 2014 11:07 AM User is offline

Thanks for the replies.

The o-rings were hard, brittle and flattened at the compressor lines, so I'm sure all the seals are the same on this 16 y/o 180,000 mile compressor. I'm going to replace all the o-rings under the hood and try again. Next step will be inspecting the evaporator and expansion valve for leaks. If that all checks out, I'll replace the compressor with another Denso from Rockauto for $190.

Is there any way to check the vacuum issue at the shaft seals? Can the seals be replaced?

masintenn on Sat April 05, 2014 10:08 PM User is offline

Figured it out! It was the valve on the low side of the gauge. As soon as I would close the valve, it would lose vacuum. Keeping the valve open and connected to vacuum pump holds vacuum perfectly. I replaced all the o rings under the hood, the drier, 3 oz oil and service valves. Pulled a vacuum for over an hour and am letting it sit over night.

Will charge tomorrow and post results.

masintenn on Mon April 07, 2014 10:23 AM User is offline

Vacuum held overnight so I pulled vacuum for another 30 minutes then charged with 28oz. A/C was blowing 40 at the center vent, but it wasn't much of a test since the weather was so cool yesterday at ~60.

I'll post a final update after we've had some hot weather. Thanks for the help!

Leggie on Mon April 07, 2014 1:52 PM User is offline

Do you use pure refrigerant for this. The vapor is soluble in oil just like nitrous dissolves in whipped cream. You won't get a meaning result. You need to pressurize with nitrogen. Dry air is usable, but discouraged these days for safety reasons as R134a + air under pressure can ignite even though 134a is not flammable under atmospheric pressures.

If the system has been out of use for a long time, it does not surprise me that it leaks vacuum. A film of oil that lubricates the shaft and the seal is very important in maintaining a seal and its important to not let the seal starve of oil as it gives opportunity for water to come in contact with the shaft which can corrode it. Corrosion on shaft of course means rough surface that can leak. Its entirely possible that the re-wetting of the seal as you messed around with it re-established the seal. It's very much like the microscopically thin oil between the engine piston rings and cylinder wall that makes the seal. If you were to pressurize oil free engine through the spark plug hole, you'll find that it will not leak down very fast relative to one with a shot of coating the cylinder wall.

masintenn on Mon April 07, 2014 7:22 PM User is offline

It was definitely the low side manifold valve losing vacuum. Even with the connectors closed and attached to the storage ports it would lose vacuum as soon as I screwed the low valve down. Brand new Harbor freight gauge....go figure!

I charged with pure refrigerant and added oil to the drier.

Jag987 on Mon April 07, 2014 11:25 PM User is offline

HF. I am as cheap as anyone else, maybe cheaper. I like getting the best bang for my buck. I was looking for a spare set of gauges and found the ones at HF for $49.99. The online reviews were all over the place, some saying they were great for the price, some saying total garbage. But for $50, I figured why not? I went in to my local store and was happy to find a new open package. After a short exam, I left them there. I was going to make a point, but can't remember what it was. I'm glad the problem was found.

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I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

Leggie on Tue April 08, 2014 7:11 AM User is offline

Quote
Originally posted by: masintenn
It was definitely the low side manifold valve losing vacuum. Even with the connectors closed and attached to the storage ports it would lose vacuum as soon as I screwed the low valve down. Brand new Harbor freight gauge....go figure!



I charged with pure refrigerant and added oil to the drier.

I have that same one, with same problem. Thing is a total POS.

wptski on Tue April 08, 2014 7:31 AM User is offline

In the HVAC world they frown at pulling a vacuum through a manifold but on the other hand they have 4 valve manifold sets with one of the ports made with 3/8" fittings just to use larger hose for faster evacuations.

I have limited experience but have already seen times where vacuum will be held but not pressure and the other way around also.

masintenn on Tue April 08, 2014 12:50 PM User is offline

I read a lot of good reviews about the HF gauges and I've always had good luck with their stuff in the past. I generally only buy HF tools that I know won't use much. Unfortunately, I don't have my receipt anymore, but as long as I know how to compensate for the problem, I suppose it's not a big deal. I may see if I can disassemble and fix it. It might be something simple like a bad seal.

Leggie on Wed April 09, 2014 2:42 PM User is offline

Quote
Originally posted by: masintenn
I read a lot of good reviews about the HF gauges and I've always had good luck with their stuff in the past. I generally only buy HF tools that I know won't use much. Unfortunately, I don't have my receipt anymore, but as long as I know how to compensate for the problem, I suppose it's not a big deal. I may see if I can disassemble and fix it. It might be something simple like a bad seal.

It is a bad seal, due to crap design.

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