Micron gauge will not hold vacuum.. tried everything, new gauge, etc.

[don87109]

Attached directly to my vacuum pump my CPS vacuum gauge quickly drifts from 50 to roughly 400 microns in about 1 minute and then drifts slowly to eventually hold maybe 900 microns.

Figuring my Yellow Jacket core puller might be leaking I bought a new Appion core puller and got the same results. Ah-ha, I figured, my CPS Micron gauge must be leaking so I bought a new one (CPS again)... Guess what, very similar drift problem... I have tried nylog, new gaskets, cleaning the old gauge sensor, even changed the vacuum pump oil, all to no avail.

Out of desperation to eliminate the core puller valves, I used my Yellow Jacket manifold requiring one hose with integral cutoff valve in the path to the gauge. Very similar results. Ok manifolds may not the best for vacuum, but I was desperate to try something.

My original equipment (micron gauge, etc) did work properly a few years ago.

Best I can figure is the micron gauges are both bad.

Anybody have suggestions?

P.S. I am a retired old engineer who got his universal certificate to just work on a couple of family AC's.

[R600a]

Cycle the valve a few times to get the moisture, refrigerant, and air out of it.
Stabilized at 900 doesn't sound like a leak.

[BBeerme]

If you've got your vacuum gauge directly on your pump through the CRT, you do not have enough 'volume'. Need to tie into something like a recovery bottle.

[2sac]

Have you changed the oil in your pump?

[vin lashon]

Moved from AOP.

[don87109]

1. Yes I have cycled the valves.. before posting I spent hours reading many of the messages on this site.
2. I have tried a "greater volume" by pumping the system lines and evap coil. Could only reach 900m and quickly rose to 2000m. I pretty sure the system doesn't leak based on days-long nitrogen test.
3. Yes, I have changed the oil in the pump.

I'll try evacuation of the system again with the new gauge if it doesn't rain today.

Thanks to everyone who replied... any more suggestions are welcome.
Frank

[R600a]

By the way just so you know the CPS micron guage is not known for accuracy.

[whp]

We use Fieldpiece Digit manifolds with built vacuum/micron. We can get to less than 300 microns and hold. Sometimes it takes a while due to moisture or small amounts of refrigerant residue in the oil. We have the Testo gauges and have never been able to get below 29.9'. It's probably a defective piece of equipment. Additionally, the vacuum pump oil can get moisture saturated and not allow for good microns. Might need to change the oil. Hope that helps

[don87109]

Bottom line after hours of tests and re-tests on the bench both gauges rise from about 200m to 750m within one minute(give or take 100microns). 10 minutes later they level off at about 1000mic and hold. I have changed the configuration to the vac using 3 different sets of equipment (including adding a manifold and hoses) and the results are the same. The gauges seem to be the logical failure point.

I'm pretty certain my system where I have changed the evap coil is leak free based on days of 150lb nitrogen pressure testing. So I'm thinking of pulling a vacuum (hopefully close to 500mic), skipping the decay test and directly proceeding with charging. As mentioned, I have changed the vac oil and am hoping I can now make 500mic.

Anybody think the above charging scenario is a bad idea? Surely it's very rare for a vacuum decay test to fail after elongated successful pressure testing, no?

Thanks again for all the replies so far. I'm looking forward to more.
Frank

[Restaurant Mech]

Even your testing contains either moisture or refrigerant.
Just pulling to 900 or 500 doesn't tell the story.
It's the decay that tells you how far evacuated the system actually is.
I routinely do a vacuum decay test that has to hold BELOW 500 microns for 24 hours.
On an average of 125 feet of line on these systems, it takes MANY pull-downs and purges to reach a true vacuum below 500 microns.
Typically if you see below 100 microns when running your pump you could be in an ACTUAL moisture free vacuum

[mgenius33]

Have you tried replacing the battery?

Time to buy a professional gauge. Kudos for at least having one, but your readings are only as good as your tools.

I switched from Appion to Hilmor VCRTs due to inconsistent results. Since, my vacuum decays now all drop to <0.2u/sec. Today it basically flatlined to 0.0u/sec. Ultimate pull down was 157.1u, final was 234.4 after 9 min at 0.0u decay. Probably could have pulled it down a bit longer, but I don't think it would have made much difference. Of course, time will tell with the longevity. My Appions were good at first as well, but their tightness slowly diminished after only a few months use.

[don87109]

1. Yes, I replaced the battery on the older gauge and the new gauge has a new battery.

2. Hard to see a moisture problem on my test setup. Two of the three test configurations were hard piped to the pump using a single VCRT and multiple pump downs. However no nitrogen purges. I'll try multiple purges/pump downs on the real A/C system this weekend. Hopefully my Vacuum pump survives.

3. If nothing above works I'll opt for a Bluevac micron gauge.

4. I guess nobody likes my "skipping the vacuum delay test" idea..

Thanks again everyone. Any other comments are welcome. I'll advise what ever I find.
Frank

[R600a]

"4. I guess nobody likes my "skipping the vacuum delay test" idea.."
I won't tell. Just use a bigger filter dryer.

[don87109]

Manufacture's specs say system must stay under 1000mic for 10 minutes and be steady.

Actually, my bench test achieved that so maybe I can achieve that with the actual ac system and multiple purge/evacuation.

It sure sounds like a moisture problem like Restaurant mech and others have said..

I'll advise what happens..
Frank

[BBeerme]

If it is moisture, the microns will go up to something like 1200-1400 then stop there. Temperature probably affects where the rise in microns will stop.

Manufacture's specs say system must stay under 1000mic for 10 minutes and be steady.

Actually, my bench test achieved that so maybe I can achieve that with the actual ac system and multiple purge/evacuation.

It sure sounds like a moisture problem like Restaurant mech and others have said..

I'll advise what happens..
Frank

[R600a]

Sorry if I overlooked it but have the gauges been cleaned?

[don87109]

I cleaned the older gauge with denatured alcohol (per manual) several times. It didn't seem to change anything. I didn't clean the new gauge as I may return it and get a Bluevac.

Thanks for the suggestion, I appreciate all the help I have gotten.

P.S. I'll try the multiple purge/evacuation suggestion soon, providing the wife doesn't have other ideas.

[Mr.Breeze]

I've had to tighten the valve core on the Schrader valves on the evaporator coil on amana units 3 or 4 times. Holds on pressure but will give on vacuum. Started tightening them before we installed em. I believe it was usually about 900 then it would jump back up to 1500 or there abouts.

[Hurst11]

If you've got your vacuum gauge directly on your pump through the CRT, you do not have enough 'volume'. Need to tie into something like a recovery bottle.

I’m voting this is his issue. With such a small volume to pull on, it don’t take much to see a significant change in micron level.
With both/all the gauges you’ve tested and different setups the results keep coming out very similar. Doing the actual process on the system should make those issues go away with having more volume to work with.

[kdang]

Did you flush the refrigerant line set ?