Problem holding a vacuum after pump down

[shaggs2broke]

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.

[monu96]

Thanks for Sharing the informative post.

[lzenglish]

Anyone have any ideas on what I could try next? Your help is appreciated.

"Yes I Do". "Your Tools are only as accurate as the last time they were tested and calibrated" When is the last time you "tested and calibrated" your "gages, vacuum pump, and hoses"? Get in the habit of doing this as much as possible.

[Gunslinger]

Pump down and pulling a vacuum are two different procedures. If you are pulling a vacuum and the level rises, try pulling the vacuum for a longer time. Also, to test your set up, pull a vacuum on recovery tank; not a length od tubing.

[Core_d]

Try putting some leaklock on all the fittings. Could also be the core tools are leaking internally. Is this a single head mini and your pulling from both lines? If you only have access to one end of the line length the pressures could just be stabilizing.


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[pecmsg]

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.

Any training, classes, online?

Where did you purchase this unit?

Its a waste but at least say your certified!

[Adlerberts-Protege]

Most manufacturers state to hold vacuum for 10 minutes under 1000 microns. Sounds like you have achieved that. What ya sweating?

[rider77]

Your pressure test is insufficient. Many manufactures call for over 500 PSI for as much as 24 hours.

[Core_d]

Your pressure test is insufficient. Many manufactures call for over 500 PSI for as much as 24 hours.

I doubt thats the case here.


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[Adlerberts-Protege]

Your pressure test is insufficient. Many manufactures call for over 500 PSI for as much as 24 hours.

That isnt happening in the real world and you know it. Lets be realistic.

[rider77]

I doubt thats the case here.


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No, but doing that low of a pressure test could come back to bite the OP.

[rider77]

That isnt happening in the real world and you know it. Lets be realistic.

I do it.

[Core_d]

No, but doing that low of a pressure test could come back to bite the OP.

I dont do hardly any if any new installs but, my nitro regulator is factory set at 250psi. Some leaks will show up even better with a lower psi.

Is um a micron? If thats the case he has a dry leak free system.


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[rider77]

I dont do hardly any if any new installs but, my nitro regulator is factory set at 250psi. Some leaks will show up even better with a lower psi.

Is um a micron? If thats the case he has a dry leak free system.


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Not sure, was wondering the same thing myself.

[pecmsg]

That isnt happening in the real world and you know it. Lets be realistic.

Mine ARE 500psig for 12 hrs!

[Adlerberts-Protege]

Mine ARE 500psig for 12 hrs!

Same thing I said to Rider. Working for someone else, they want that job done that day. So let us sit and laugh at this scenario. I am going to tell my boss and the customer that it is on test and I will be back at midnight, tomorrow, maybe the following day? You guys crack me up.

I pressure test and go eat lunch. When I come back and it is holding I then proceed to pull a vac. You expect your customers to tolerate that between April-Sept.? Do not, do not, try that crap on me. Which is exactly what it is. Complete crap.

[shellkamp]

Same thing I said to Rider. Working for someone else, they want that job done that day. So let us sit and laugh at this scenario. I am going to tell my boss and the customer that it is on test and I will be back at midnight, tomorrow, maybe the following day? You guys crack me up. I pressure test and go eat lunch. When I come back and it is holding I then proceed to pull a vac. You expect your customers to tolerate that between April-Sept.? Do not, do not, try that crap on me. Which is exactly what it is. Complete crap.

A boss who is even halfway intelligent knows that the small investment of time on the pressure test now, where only nitrogen and time are at risk, is much better than getting the emergency call in the middle of July and finding the charge completely empty due to a faulty braze joint.

Remember, you're not just losing your hourly rate plus materials when you gotta go do something like that, you're losing out on the opportunity to go out on a billable call, the gross profit on the refrigerant and materials you're now giving away for free, plus it's going to take you doing X amount of billable (and profitable) work just for you to "break even" from the loss of labor and materials you used on that warranty call.

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[shellkamp]

Your pressure test is insufficient. Many manufactures call for over 500 PSI for as much as 24 hours.

Let's put a disclaimer on that - that's only going to be for coils and line sets. You can blow a compressor up if you pressurize the shell that much.

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[rider77]

Let's put a disclaimer on that - that's only going to be for coils and line sets. You can blow a compressor up if you pressurize the shell that much.

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Actually I can’t agree with that.
On my VRF systems, they are very specific instructions for leak checking.
Let’s use Samsung as an example, they specify 590 PSI for a minimum of 24 continuous hours for leak checking. This is on initial startup, with the condenser isolated and charged with refrigerant, as well as repairs after startup.
Just now, I’ve had an older Plus-3 VRF sitting at 500 PSI for about a month while I’ve been waiting on a high pressure transducer to come in.
And no, I’m not worried about time. Or getting done quickly.
If I need to leave it pressurized and come back tomorrow, that’s what I’ll do.

[shellkamp]

Actually I can’t agree with that.
On my VRF systems, they are very specific instructions for leak checking.
Let’s use Samsung as an example, they specify 590 PSI for a minimum of 24 continuous hours for leak checking. This is on initial startup, with the condenser isolated and charged with refrigerant, as well as repairs after startup.
Just now, I’ve had an older Plus-3 VRF sitting at 500 PSI for about a month while I’ve been waiting on a high pressure transducer to come in.
And no, I’m not worried about time. Or getting done quickly.
If I need to leave it pressurized and come back tomorrow, that’s what I’ll do.

I'm not saying you'll definitely blow up a compressor, but it can happen. You can definitely deform the shell.

If you have manufacturer literature that specifies leak tests (at that high of a pressure) after repairs with compressors in the circuit then I'd like to see that. So far the highest recommended test pressure I've found from a manufacturer is about 362psi (25 bar)

Actually - let me put another disclaimer on that. The high side of the system can easily tolerate that pressure, it's the low side that cannot, as the low side just dumps directly into the compressor shell.

And then of course there's compressors used with CO2, and I suppose those would absolutely need to be able to tolerate those kinds of pressures.



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