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Old 08-19-2013, 07:22 PM   #1
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Cant seem to evacuate very well. Do I have a leak or just moisture?


Cant seem to get it to stay below 1000 microns.

Mitsubishi mini-split all new install. Prefab line set with properly torqued and nylog'd fittings. New vacuum pump and oil.

Evacuated once, got to 780 microns in an hour or more. As soon as I blanked off, it started to rise. An hour later it was up to 1440 but appeared stable. If I had kept watching, it might have kept going up, not sure.

I concluded it's moisture, so I pressure tested to 360 PSI. It held but did drop 1 PSI in half an hour, which I attributed the temperature change.

I assumed it would then evacuate well after pulling out all the dry nitrogen.

I was wrong. Evacuated again and got down to maybe 880 microns in half an hour. But as soon as I blank off at the core tool, again it begins to rise. In 10 minutes its over 1100 and rising.

I repeated the purge / evacuate a couple more times. I cant really tell if it's getting better each time as I haven't had the patience to give it another hour each time and see exactly how high it rises.

I'm doing another pressure test now at 351.8 PSI. (BTW, anyone want to confirm that 1-2 PSI drop in an hour is insignificant as I believe?)

So, what do you guys think? Is there a leak, or do I really have that much moisture to pull out? It is a rather humid day here in So Cal.

Thanks all. --Upton O Good

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Old 08-19-2013, 07:33 PM   #2
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Cant seem to evacuate very well. Do I have a leak or just moisture?


anything below 5000 Microns is moisture could be the refirg oil in the compressor absorbs moisture during install.1000 to 1400 rise is still tight...tip always check your gauges with a vac/micron test especially individual hoses with the micron gauge directly to the vac.vac pumps sitting in the sun running might not go below 500mics with the heat of the motor and sun..banging it.on the PSI test hit the brazed fittings/locking nuts into the condenser if you have them.. and that drop is nothing


Last edited by biggles; 08-19-2013 at 07:37 PM.
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Old 08-19-2013, 09:24 PM   #3
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Cant seem to evacuate very well. Do I have a leak or just moisture?


Thanks a million to biggles for the information. I feel better.

I pulled a vacuum on the manifold + vacuum gauge + hoses as suggested. All got down below 500 in short order.

The unit comes pre-charged, and the charge has not yet been released. I'm only evacuating the line set and air handler. The compressor section is still sealed, so any moisture there would not come out.

I did a leak check at 4 fittings, all good; 2 at the unit and 2 at the air handler. Simple soap bubble check, not fancy electronic thingy.

I'm now pulling down the unit once more. Its at 780 in 15 minutes. I'm hoping to stay under 1000 when blanked off. But I'll give this pump an hour and call it good.

Any other opinions, advice, or experience are most welcome.

--Upton O Good
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Old 08-20-2013, 06:47 PM   #4
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Cant seem to evacuate very well. Do I have a leak or just moisture?


if you put the vac gauge on one single hose direct to the vac pump it should go down to 100mics or even 25 mics...within 15 minutes.to do the gauges use one hose from the vac to the middle port and one to the vac gauge from either hi or low side cap the unused manifold port...run the pump should also pull down below 100 mics easy. 500 over all is still tight to intro the Freon there..
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