For me, that's not an easy question to answer. It depends on a lot.
Small system, less than 50 tons:
If it's just a repair, been open less than a day, minimal fittings/joints touched, 500 microns and go. Low or flat, 500 microns and let sit valved off for an hour and see.
Over 50 tons:
Evac to 500 microns and let sit for at least an hour no matter why I'm working on it.
Chillers over 300 tons:
Even if it's a high pressure chiller, 500 microns with a 24hr evacuation test. If it passes, touch up the vacuum to 500 microns before charging.
The only time I'll charge over 500 microns, is if I can't get it down in time. Has to be dropping still, not just hanging out at whatever. I will notify the customer and let them know the options. If they want it right, I'll stay or evac overnight.
I refuse to charge above 1000 microns.

Sent from my SM-G935U using Tapatalk

 

And when the server room crashes because you wouldn't add the freezey juice until a proper repair can be made?

There's a lost account.

For me, that's not an easy question to answer. It depends on a lot.
Small system, less than 50 tons:
If it's just a repair, been open less than a day, minimal fittings/joints touched, 500 microns and go. Low or flat, 500 microns and let sit valved off for an hour and see.
Over 50 tons:
Evac to 500 microns and let sit for at least an hour no matter why I'm working on it.
Chillers over 300 tons:
Even if it's a high pressure chiller, 500 microns with a 24hr evacuation test. If it passes, touch up the vacuum to 500 microns before charging.
The only time I'll charge over 500 microns, is if I can't get it down in time. Has to be dropping still, not just hanging out at whatever. I will notify the customer and let them know the options. If they want it right, I'll stay or evac overnight.
I refuse to charge above 1000 microns.

Sent from my SM-G935U using Tapatalk

 

My general rule is pull below 500, then blank off, you do not want to see a rise above 1000 in ten minutes.

But that is for smaller RTU's. You gotta a bigger system, then you need to adjust the time of rise. Sometimes the best course of action is to do the quoted repairs, then use weasel words to disclaim any other leaks that are unknown.

 

Oh, this is a resi thread.

Oh well, all of the same principles apply.

 

I'll pull to about 300 and then block off and watch for 10 minutes. If it settles at under 500 it's charge and go. If it climbs to over 500 and then settles at under 1000 I'll pull it back to 300 for another 15-20 minutes and repeat to see if it'll stay below 500.

I've questioned my gauges and hoses from time to time and will use a 1/4" flare coupling to connect my high and low hoses to and put my micron on the charging hose. Pull 100 microns on the setup and let it sit for an hour. Most times if it climbs it's because there is oil or something in it from a previous job, then I flush them out and test again. Never had a set of hoses not hold a worse vacuum than what I wanted a system to hold, but then again I change hoses every 3 years.

 

Sounds like new install work?

My charging hoses and manifold would never hold a good vacuum. At least, that is my guess. Only a guess, since I never use them for vacuum work.

 

New drier
Pressure test
Evacuate
Recharge

Holding a vacuum to check for leaks is crazy.

You just pressure tested and had no leaks otherwise you should have never put the pump on.

So is it a leak or is it just a incomplete evacuation a just silly talk.

 

If they were that hard up and really needed it, I would. Just would get it in writing that it is outside the realm of normal practice and not liable for any issues.
Edit: And I forgot to quote you BBeerme...

Sent from my SM-G935U using Tapatalk

 

Since this forum covers residential work, i guess we assume the equipment under 5 tons.

If a simple nitro test is sufficient, i wonder why all the pump mfgs insist on a finished vac of __ microns?

Then not particularly residential, but if you ever get on a government job, you are likely to face a requirement of holding __ microns for 24 hours, period, and an inspectors check. Otherwise they will not pay, so someone thinks the test is real important!

How common are triple evacs? As mentioned in the op, it has to add a few hours to a job, so I'd guess they're not commonly done.

 

The micron level is to ensure the system is dry and as free of contaminates as possible. A vacuum can only reach 14.7 psi of negative pressure. I don’t know of anyone that pressure tests at 14.7 psi of nitro. If a system doesn’t leak at 400+ psi with a smaller molecule of nitro then it won’t leak with refrigerant.

And even if somehow you have a leak that only shows up in a vacuum, how many systems operate in a vacuum? (I’m trying to make a point so don’t mention pumpdown systems 😁 )

 

usually valves have some leaks. when you close them some amount of air will leak into the system. However then the vacuum should hold.
I usually see some rise when I close the valve to the vacuum pump but then the micron level drops slowly (the air you let in distributes in the pipes) when your system is tight, otherwise you will see it rising instead.

 

Using a new Sman and new Robinair hoses, I pulled a test vacuum on JUST the sman and hoses. I pulled to 500 microns then watched a rise to 1800 and a fall within an hour to 1100. The 1100 held tight for 24 hours. My hoses are not vac rated.

I tried the same test with a new, generic hose set with similar ratings. This time I pulled to 500 and watched a fast rise through 9000 microns and then on to -28.0 I think we can say those hoses are no good for precision vacuum work.

All the pump mfgs say that any vac to 300 that rises above 5 or 600 microns, indicates a system leak or water under the comp oil. At this point I'm not so sure.

Pulling vacuums on attached hvac systems often gives me different results. Sometimes I get a rise from 300 to 700 and stop. Other times I'll see rises through 1500 and stop. Other times I'll see rises to 1500 and still a very slow rise that continues. You never quite know whether to blame the hoses, the gauge, moisture under comp oil, or a leak,

If you can't pull a vacuum to 300 on JUST a new quality manifold and hose set, and hold below 500, how can anyone expect to consistently acheive a rise to LESS than 500 when attached to an hvac system?

Have others tried to pull test vacuums on just their manifold and hoses? The results may surprise you.

 

Here is what Lennox says on vacuum.
"evacuate the line set and indoor unit until the absolute pressure does not rise above 500 microns within a 20−minute period after shutting off the vacuum pump and closing the manifold gauge valves."

If one can't hold 500 on JUST a manifold and hose set, how are you going to hold 500 on an entire system?

 

DON’T use a manifold and hose set for vacuum work! Using that setup will add hours to your day. Use Appion valve core tools with large diameter vacuum rated hoses and a micron gauge. Leave your manifold in the truck.

 

This video by measure quick/ fieldpiece, does a excellent job explaining how to use a micron gauge for testing system tightness.
https://youtu.be/ElwcSEeLXAI?t=1089
I really want to get me one of those Bluetooth micron gauges.

 

Excellent video by Fieldpiece.

Not sure about others, but barely a word of what's explained in the Fieldpiece video was taught in our tech school. (perhaps some do) Close as we got was, pull it down to 300, even if it takes hours - and you figure out the rest!

So unless you came up under a lead tech who had figured out issues like vacuum line size and vacuum decay, you could still be tring to figure all this out.

Others have figured this out too and lots seem to have settled on the YJ 3/8 vac rated hoses vs. the huge 3/4 hoses in the video. The pump in the video seems way too big for residential, and I gather that for residential guys somewhere around 5 or 6 cfm is aplenty.

Many thanks to JustaHvacGuy as he's right on the money. Awesome tip!

 

The video is pure BS. The minimum micron level has nothing to do with hose size per se. In fact given similar construction the larger surface area of the larger hoses would allow a higher rate of permeation. The benefit of larger hoses is in faster pull-down time due to improved flow rate, period.

As to your previous question, the reason that the rig when isolated will show a faster rise is that it has a much smaller volume. A rig that rises 1000 microns a minute when isolated might show no rise at all over 24 hours when open to a system of sufficiently large volume.

Also it was suggested somewhere that a positive pressure test is better because of the much greater pressure difference across the leak(s). That seems to be a reasonable conclusion, problem is it just doesn’t work that way in reality. I’ve done the math here before that explains this. The vacuum test offers much greater precision, which allows detection of leaks with tremendously smaller changes in system pressure.

 

Reading Appion and Yellow Jacket specs for vacuum rated hose, they are of different construction that won't allow pressure migration or vacuum pressure decay. They clearly show the long 1/4" hoses won't allow as deep a vacuum and it takes 10x longer.

It mirrors what I found with non-vacuum rated hoses. You won't get a good vacuum and you will waste many hours waiting needlessly, potentially thinking you have a leak, when you don't.

It looks like the smartest techs, up on best practices, are using 3/8 or larger vac rated hoses, and bypassing their manifolds entirely.

 

 

BBeerme, did you go to my truck and steal my stuff? Same pump, hoses, and valve core tools. I think the scratches on your pump label are close to the same as mine as well. Funny.

 

LOL

Are you missing any micro BluVac's?

 

Maybe. I’m actually sitting on the deck at the cabin and not working for the first time this Summer. My whole van could be missing for all I know, and at the moment, I don’t even care. :cheers:

 

When I go to the mountains, first thing I do is drink a beer at 8 AM.

Then proceed to get the truck stuck.

Gawd, I loved that ol' Suburban. Knew I could beat the hell out of it, because, well, just because I could.