Hi Everyone. I am new to the site but have been reading a number of threads and am finding them very useful. My background is in construction but I decided to branch out and start installing ductless mini-splits. I completed my first install and performed a 40 minute pressure test @ 250psi. I proceeded to the last step of vacuum pump down and this is where I ran into problems. My vacuum setup is as follows: two Appion core removal tools, an Appion 1/2" vacuum hose and CPS vacuum gage. I pulled down under 500 microns quickly and closed the valve to isolate the vacuum pump from the system. The value immediately went up to several thousand and slow increased so I re-opened the valve and allowed it to pump down awhile longer. After several attempts I got it to remain initially at 400um. It didn't stabilize however and kept creeping up around 20-40um per minute. I wasn't sure if it was my system leaking or my connections so I brought my equipment home to see if I could hold a vacuum with a simplier setup. This setup involved one Appion core removal tool, a vacuum gage, a T-valve and about 3' of 1/4" line with plugged flares. I would post a pic but am too new to do so. This time I pressure tested my setup at 620psi for 24 hours. Pressure was good after 24 hours so I released the nitrogen. I started Pulling a vacuum and again when closing the valve the value would creep up. I don't understand why I can't hold a vacuum after holding 620psi after 24 hours. I am not sure if my vacuum gage is the issue or something else. Anyone have any ideas on what I could try next? Your help is appreciated.
Problem holding a vacuum after pump down
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shaggs2broke
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Where is someone trying to get in the required technical post count supposed to post. I know reviving old threads isn't totally ideal but at least he is putting in the effort.
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nonsense
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There is such type of leak that leaks only in one direction. Holds pressure but leaks under vacuum (or vice versa). It's real
Care to elaborate?
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I've never seen a proper vacuum pulled with the cores in and I don't believe it exists.I'm still hung up on the 12 hours to vacuum down a 4 ton system without pulling the cores
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over 24h the climatic conditions change too much for any useful conclusion. Pressure depends on temperature. Now if your temp changed 3F, is the drop by 20 psi a leak or temperature drop? You cant even measure the temp across all lines, indoor, outdoor etc. So no, more than 15-30 mins is not useful
I use this calculator for long pressure tests for exactly this reason.
https://www.oceanhvac.com/nitro.php
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But it definitely changes pressure.
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Yep and even more accurate if you compensate for temperature.
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Ice posted it!
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The link above works too.
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