Standing vacuum test on mini-split

[lemmy999]

I am getting ready to install a 9k BTU mini-split. I have a vac pump and a new CPS VG200 micron gauge. The instructions I have read say to use a couple of valve core removal tools, a vac pump and micron gauge then pull a vac to around 200 microns, valve off the vacuum pump and turn it off. Then let the system set with the micron gauge still on the suction access port and wait for 10 minutes. If the vacuum hasn't risen by more than 200 microns then everything is good and you are ready to release the refrigerant from the system.

I wanted to test the pump, hose, valve core removal tool and the micron gauge before I hooked it up to the mini-split. The pump easily pulled a 200-220 micron vacuum. I then valve off the micron gauge, turn off the pump and the VG200 reading starts to rise. In about 10 minutes it went fromm 210 to 380. I assumed there was some leakage around the valve on the valve core removal tool so I tried again. This time I turned the valve on the valve core removal tool at 200 micron but left the vacuum pump on (so it was keeping a vacuum on the hose that is on the other side of the valve core removal tool). Ten minutes later it was at 370. Since it isn't leaking past the valve on the VCRT, it seems to me that it must be leaking where the VG200 connects to the VCRT, which is just a male flare. I have tried two different VCRTs and the results were the same. I plan on buying some nice Appion VCRTs, but since it isn't leaking past the valve, I'm not sure how that will help. Any ideas why this is happening?

 

[FredWanaker]

yes. There is a leak. Been awhile since working on these but I think you can pressurize the system with Nitrogen, and look for bubbles or sounds. Then once fixed, start over.

 

[lemmy999]

yes. There is a leak. Been awhile since working on these but I think you can pressurize the system with Nitrogen, and look for bubbles or sounds. Then once fixed, start over.

I guess I was too wordy and it wasn't clear. I haven't hooked anything up to the system or done the nitrogen test on the system yet. I was just testing my vacuum pump, hose, VCRT and gauge. So what I have is essentially:

pump -> hose -> shut off valve -> micron gauge.

I open the shut off valve and run the pump until the micron gauge is at 200 (first picture). Then I turn off the shut off valve and the micron gauge drifts up to about 380.

There is still a vacuum on the hose, so the only place there could be a leak is either inside the micron gauge (not that likely as it is brand new and a high quality gauge) or where it connects to the shut off valve (a flare connection).

If I let it sit for hours it will get up to 520 or so. It slows significantly after it gets to about 350 or so.

 

[428PI]

I think you'll be sorry messing with the valve core. Personally I would just vacuum it sufficiently and pressurize with nitrogen and test with soapy water on connections. But what do I know. Since installing my dual mini split I had to add a couple pounds freon because it was freezing my evap coils after one year.

 

[lemmy999]

I think you'll be sorry messing with the valve core. Personally I would just vacuum it sufficiently and pressurize with nitrogen and test with soapy water on connections. But what do I know. Since installing my dual mini split I had to add a couple pounds freon because it was freezing my evap coils after one year.

I don't plan on removing any valve cores as I think that is just to speed up the job a bit..but increases the risk of something going wrong. I am just wanting to use them so that I can valve off the pump and the micron gauge so that oil doesn't get on the micron gauge when I'm holding a vacuum (I've heard oil from the pump can come up into the hose if you turn off the pump and leave a vacuum in the hose) and also protect the micron gauge from refrigerant.

 

[danski0224]

I guess I was too wordy and it wasn't clear. I haven't hooked anything up to the system or done the nitrogen test on the system yet. I was just testing my vacuum pump, hose, VCRT and gauge. So what I have is essentially:

pump -> hose -> shut off valve -> micron gauge.

I open the shut off valve and run the pump until the micron gauge is at 200 (first picture). Then I turn off the shut off valve and the micron gauge drifts up to about 380.

There is still a vacuum on the hose, so the only place there could be a leak is either inside the micron gauge (not that likely as it is brand new and a high quality gauge) or where it connects to the shut off valve (a flare connection).

If I let it sit for hours it will get up to 520 or so. It slows significantly after it gets to about 350 or so.

You need to wander over to the True Tech Tools (TTT) website and watch their free videos on pulling a vacuum on residential HVAC systems. It will help you understand your equipment and they have some methods and equipment that will save MAJOR time in the vacuum pulling process. They also have a YouTube channel. Jim Bergmann has put out a wealth of knowledge for FREE.

There's a lot of other HVAC themed videos on YouTube, but you really have to be careful because like here in this forum, there's a lot of BAD info, and you have to know enough to sort it out.

Yes, you want to remove the Schrader cores to pull a vacuum. Yes to a large diameter vacuum hose, even if the fitting side is smaller. There is physics behind this, and an explanation over at TTT.

Mini-split access ports are typically 5/16", not 1/4".

Yes to Nylog on connections.

The shut off valve on a vacuum pump is NOT reliable and NOT vacuum tight. Absolutely do NOT depend on it to isolate the system.

Your hoses are NOT vacuum tight.

Oil in a vacuum pump needs to be changed frequently (or, warmed up and changed before using it).

The valves in VCRT's are not necessarily vacuum tight, either. They need to be cycled to clear the stuff trapped in the ball port when opened.

Do be aware that there is NO official procedure or standards to attain "Vacuum Certified" or "Vacuum Rated" marketing hype for HVAC stuff, although Appion is generally regarded as the upper tier of "non certified" "vacuum rated" stuff in marketing speak.

The smaller the system you are testing, the more readily that problems with your equipment become apparent. The vacuum pump, VCRT and micron gauge is the definition of a SMALL system. Your results are actually quite good.

If you read the evacuation procedure for a bunch of residential equipment, it is usually pull down to 400-450 microns, blank off, wait 5 minutes, and if it doesn't rise over 500 microns, it's good.

Read your own manual to be sure.

In any event, a standing vacuum test with a micron gauge is NOT a 20 minute test. If there is a leak or excess moisture, it will show up quickly.

 

[bluedog225]

Subscribed. Good info.

 

[lemmy999]

You need to wander over to the True Tech Tools (TTT) website and watch their free videos on pulling a vacuum on residential HVAC systems. It will help you understand your equipment and they have some methods and equipment that will save MAJOR time in the vacuum pulling process. They also have a YouTube channel. Jim Bergmann has put out a wealth of knowledge for FREE.

There's a lot of other HVAC themed videos on YouTube, but you really have to be careful because like here in this forum, there's a lot of BAD info, and you have to know enough to sort it out.

Yes, you want to remove the Schrader cores to pull a vacuum. Yes to a large diameter vacuum hose, even if the fitting side is smaller. There is physics behind this, and an explanation over at TTT.

Mini-split access ports are typically 5/16", not 1/4".

Yes to Nylog on connections.

The shut off valve on a vacuum pump is NOT reliable and NOT vacuum tight. Absolutely do NOT depend on it to isolate the system.

Your hoses are NOT vacuum tight.

Oil in a vacuum pump needs to be changed frequently (or, warmed up and changed before using it).

The valves in VCRT's are not necessarily vacuum tight, either. They need to be cycled to clear the stuff trapped in the ball port when opened.

Do be aware that there is NO official procedure or standards to attain "Vacuum Certified" or "Vacuum Rated" marketing hype for HVAC stuff, although Appion is generally regarded as the upper tier of "non certified" "vacuum rated" stuff in marketing speak.

The smaller the system you are testing, the more readily that problems with your equipment become apparent. The vacuum pump, VCRT and micron gauge is the definition of a SMALL system. Your results are actually quite good.

If you read the evacuation procedure for a bunch of residential equipment, it is usually pull down to 400-450 microns, blank off, wait 5 minutes, and if it doesn't rise over 500 microns, it's good.

Read your own manual to be sure.

In any event, a standing vacuum test with a micron gauge is NOT a 20 minute test. If there is a leak or excess moisture, it will show up quickly.

thanks. I have the AC Service Tech book (by Craig Migliaccio) and also watched many of his videos several times. Like you said, there are lots of bad videos out there. I had not heard of True Tech Tools, I will check out those videos.

Craig definitely says to remove the valve cores. I thought that was just to speed up the process, I wasn't sure if it actually did a better job with them removed. I am just a bit apprehensive about releasing the refrigerant into the lineset and then trying to get the valve core in and having issues getting installed with pressure in the system. Craig fully release the refrigerant and then installs the valve core to the access port. I saw someone else mention just releasing a little bit of the refrigerant to get a slightly positive pressure in the lines, then installing the core. That way even if something goes wrong, you do not lose all of your refrigerant.

Craig has a video where he pulls a vacuum on the system to 200, then he turns off the pump and waits 10 min and it rises to 370 and he says that is good and moves forward with releasing the refrigerant. But I was just concerned that the small area between the valve and the micron gauge, which had only one connection) was dropping form 200 to 380. I know that the hoses and the VCRT valve can leak, but that is why I kept the vacuum pump on after I turned the valve on the VCRT to isolate the gauge. But I never considered that the smaller the system is, the more an extremely small leak can make the pressure rise a fair amount. But now that you mention it, it does make sense that would be the case. One molecule getting past a connection in a small area will raise the pressure of that small area much more than one molecule getting past a connection on a full system.

I currently have a 5/16 and a 1/4 VCRT and a bottle of Nylog. My vacuum pump has brand new oil.

My vacuum pump doesn't have a shutoff valve. I was going to depend on the shutoff valve on the VCRT to isolate the system once the vacuum is pulled on the system. Craig Migliaccio uses Appion VCRTs and uses them to isolate the system from the hose. Craig mentions "vacuum rated" in regards to hoses and his VCRTs..interesting that it isn't REALLY an official rating.

Thanks again for the great info!

 

[danski0224]

Craig fully release the refrigerant and then installs the valve core to the access port.

This is how it's done.

It's impossible to "release just a little bit" and then install the Schrader cores.

You put the Scrader core in (after releasing refrigerant), close the valve on the VCRT, remove the cap/rod then slowly open the valve. This is the check. There should be just a little pffft when the valve is opened.

 

[fitter30]

When ever dead heading a pump they always rise with a micron gauge. If you look at vacuum hoses for your manifold don't be shocked at the price. With any refrigeration oil other than mineral they love moisture and don't want to give it up and your not dealing with mineral. If your pump can pull 200 microns through manifold hoses your good.

 

[American Locomotive]

The big problem with minisplits is they usually only provide you with one external service port. If you leave the schrader core in place, you can very easily pull what seems to be a great vacuum on your gauge, but the system could still be at much higher pressure. Removing the core helps greatly speed the process.

On a side note: I used the same valve core tool you have pictured to do a bunch of minisplits. I connected the gauge to the side port, and the vacuum pump to the "core removal" port.

The ball-valve seal on the cheap VCRT seems really suspect, and I could get my micron gauge to read higher and higher just by cycling the valve while the vacuum pump was still running and connect. It got the job done, but just barely.

 

[lemmy999]

The big problem with minisplits is they usually only provide you with one external service port. If you leave the schrader core in place, you can very easily pull what seems to be a great vacuum on your gauge, but the system could still be at much higher pressure. Removing the core helps greatly speed the process.

On a side note: I used the same valve core tool you have pictured to do a bunch of minisplits. I connected the gauge to the side port, and the vacuum pump to the "core removal" port.

The ball-valve seal on the cheap VCRT seems really suspect, and I could get my micron gauge to read higher and higher just by cycling the valve while the vacuum pump was still running and connect. It got the job done, but just barely.

Yeah that is how I plan to do it when I am connected to the system. Actually I plan on using another core removal tool hooked to the side port, just so I can valve off the micron gauge when I release the refrigerant. I'm not sure if that has to be done, but I have seen Craig Migliaccio do it and it seems like a good thing. He removes the valve core from the side port of the one attached to the service port so that the micron gauge can get a better reading. But I guess it is even more opportunity for something to compromise the vacuum.

When I had it hooked up the way it is shown in the pic it would start rising when I i closed the valve (isolating it from the hose/pump), but as soon as I cycled it back it would start going down again. Just cycling it multiple times was not making the micron gauge read higher and higher.

 

[FredWanaker]

sometimes people have new hose sets, and sometimes they have old ones lying around from prior use on R12, R134, R22, etc.. The rubber seals inside the threaded couplings do go bad over time. You may want to replace them unless it is a new set of hoses and gauge. You have a leak and need to find it before charging the system. Any moisture in the air that is pulled in will cause a reaction that can create an acid.

 

[lemmy999]

sometimes people have new hose sets, and sometimes they have old ones lying around from prior use on R12, R134, R22, etc.. The rubber seals inside the threaded couplings do go bad over time. You may want to replace them unless it is a new set of hoses and gauge. You have a leak and need to find it before charging the system. Any moisture in the air that is pulled in will cause a reaction that can create an acid.

The hose is new, but the hose isn't even part of it because it is valved off and completely removed. It is like this:

Pump -> Hose -> Valve - > Micron gauge.

After the vacuum is pulled on the micron gauge, the valve is closed and the pump and hose are completely removed. It is just a closed valve (in a VCRT) and a brand new micron gauge.

 

[pcmeiners]

Micron gauges go up due leaks, line off gassing and moisture. If it continues to rise, you have a leak, or moisture. Redo the vacuum. Keep the vacuum going for a couple hours, then retest. Do not release until you can hold under 500 micron, if you can't a system leak exists or your hoses /valve/gauge leak. Hoses seals/fitting may be leak free but the hose material may be permeable at lower micron levels.
Brand new micron gauges can leak, had (2) leak on arrival.