Vacuum tests results - Nitrogen Purge needed?

[motterpaul]

I have one mini-split where a vacuum to 280 takes 25 minutes and it goes up and down and seems to get stuck at certain numbers for quite a while. It'll hit 1250, go back up to 1300 (for example), and then bounced around between them before it goes lower. Happens all the time.

Then on the other system, the pump takes it right down to 250 in 5-minutes with no fluctuations.

The setup is identical on both systems, same pump, 2 VCRTs and a CPS Micron gauge.

Both are older systems. #1 lost its refrigerant due to a twisted flare during installation but it held its charge for three years before it gave up. I am now rebuilding it and using nitrogen for a positive pressure test, and a micron gauge for the vacuum test. I also got a real torque wrench (not automotive) for the flares.

Both systems held the nitrogen perfectly for several hours, but my vacuum "hold" goes from 280 up to about 780 on both systems. System 2 was just recharged and still had some R410a in it, but not enough so I pumped it down for now. It held nitrogen perfectly for 30-minutes. The vacuum HOLD test was similar to #1.

I am wondering if I have a flare problem. I hate to take the flares apart because they test perfectly with nitrogen & bubbles. My gut says that positive pressure is more important and that if everything is holding great with nitrogen then the vacuum process was really more about getting moisture out of the lines. So, I should carry on and finish the job.

Or am I wrong? Would you do a nitrogen purge where you open the service port, undo the high side flare at the outside and push nitrogen through? Or am I thinking too hard about it?

 

[American Locomotive]

If it passed the pressure test, fluctuating vacuum is likely oil offgassing or still some trapped water vapor.

Let it run for a few hours.

 

[motterpaul]

I assume you mean the vacuum - yeah, I thought about that. Lots of oil but that's OK. If it is doing what I hope - getting the moisture out. But I also wonder about any oil trapped in the lines and think maybe a nitrogen flush is better. These systems are four years old and were installed with loops in the line set (which I just took out). When I undid the first 1/4" one, oil actually dropped out of the pipe.

 

[jjrbus]

When I ended up in that situation according to the net I had a leak or needed to blow through the liquid and gas line to move the oil up against the walls of the tubing. As I moved things around I suspected the micron gauge was bad, but hooking it to the pump would quickly draw down to low microns. I started to suspect the VCRT, I ordered a new one and problem went away. Ordered the same VCRT you have. Did the oil clear up while I was waiting or was the tool leaking? All this fun can be very frustrating!

When I first installed these mini's I left the liquid line loose at the condensor and ran nitrogen through the system to make sure everything is open. Then Torqued the nut, I did not know I was performing a nitrogen flush. Good luck

 

[motterpaul]

When I ended up in that situation according to the net I had a leak or needed to blow through the liquid and gas line to move the oil up against the walls of the tubing. As I moved things around I suspected the micron gauge was bad, but hooking it to the pump would quickly draw down to low microns. I started to suspect the VCRT, I ordered a new one and problem went away. Ordered the same VCRT you have. Did the oil clear up while I was waiting or was the tool leaking? All this fun can be very frustrating!

When I first installed these mini's I left the liquid line loose at the condensor and ran nitrogen through the system to make sure everything is open. Then Torqued the nut, I did not know I was performing a nitrogen flush. Good luck

Yeah - pushing the oil up against the walls is what I meant by "nitrogen purge." There are so many terms I probably get them mixed up. I just discovered the Reddit Minisplit group and they seem to have a completely different vocabulary.

By the way - how did that "nitrogen purge" that you did with the liquid line open work out for you? I have only heard them mentioned and don't know much about it.

BTW: the $61 Appion VCRT is worth it. The ball valve clicks into place. I also bought a cheap one first and it didn't hold.

 

[jjrbus]

Yeah - pushing the oil up against the walls is what I meant by "nitrogen purge." There are so many terms I probably get them mixed up. I just discovered the Reddit Minisplit group and they seem to have a completely different vocabulary.

By the way - how did that "nitrogen purge" that you did with the liquid line open work out for you? I have only heard them mentioned and don't know much about it.

BTW: the $61 Appion VCRT is worth it. The ball valve clicks into place. I also bought a cheap one first and it didn't hold.

I did that when I first installed the lines, had no oil in them and I have nothing to compare it too. The only thing it did was give me comfort knowing that everything was open and the nitrogen could flow thru the system.

The Appion is definately higher quality than the CPS that came in the Daikin mini install kit.

Wish I could find a more technically orientated mini group. I am getting nowhere with my L5 error code on a different mini.

 

[LS6 Tommy]

If it passed the pressure test, fluctuating vacuum is likely oil offgassing or still some trapped water vapor.

Let it run for a few hours.

X2. Evacuation wasn't long enough.

Tommy

 

[fitter30]

System R410? If it is uses POE oil which is hydrophobic (likes moisture). Change oil in vac pump let pump run 8 hours and it is what it is. The only way to successfully get to moisture out is to drain and refill and with a residential scroll compressor theirs no provisions. If its spit system install a over size drier.