I pressure check with 200psi of nitrogen. Then I check all the joints with snoop or other liquid leak detector. Do a standing pressure check for 30 min to 1 hour (overnight if possible). If there is no drop in pressure pull a vacuum to 200-300 microns, then isolate vacuum pump and make sure there is no rise in pressure above 500 microns.

 

There are quite a few threads on this site about this subject. The biggest issue seems to be proper tools. If you have cheap hoses and gauges, don't expect accurate results, nor optimizing labor.
If you spend the money on quality tools, you can typically cut down on vacuum time and pressure testing. If you have slight leaks in you hoses or gauges, you will spend twice the amount of time necessary chasing your tail for a leak that doesn't exist.
Without a quality micron gauge, and well sealed hose connections, pulling a vacuum, will simply be a time and guess scenario. You might run the vacuum for an hour when you only needed 15 min.
My suggestion, spend the money and get a good gauge and hose set up. Taking proper care of them is also very important. If you do, I assure you, the relief of stress from chasing non existent leaks will more than outweigh the cost.

 

Thanks for your replies. I guessed there are probably lots of threads already, but to be honest I get lost in the terminology as I haven't learned it in English, and US guys might use different terminology to European! I wanted to be sure we're talking about the same thing, not gas or water pressures in heating systems or something else :grin2:

I was mainly hoping to hear about people's opinions and experiences on methods. For example, many have told me it's pointless and unnecessary to pressure test using nitrogen. (I do it anyway, I don't see how it can be pointless). Also length of vacuum time, vacuum levels reached, etc. I'll try and find good threads on here

I use a Refco manifold and hoses, Robinair vacuum pump, ITE 54V vacuum gauge and Gloor nitrogen regulator. I pressure test with the hose from the Gloor straight into the unit, not via the manifolds. Then I hook everything else up and evacuate the system. Here's a few pictures:

 

on mini splits I also pressurize the lineset with nitrogen. I usually also go up to around 200 psi but always check your install instructions to make sure they don't recommend using less pressure just in case. then get your soap bubbles and soak each mechanical fitting then let the pressure sit and see if it falls. I know other techs that will put in about a pound of the refrigerant that the system uses, in this case 410a and then back that up with nitrogen up to maybe 100 psi and use a leak detector. This method contaminates the refrigerant you put in the lineset and also you will have to recover it or release which is not what anyone should be doing. also this method you cant go by holding pressure because the refrigerant pressure is going to change on the temperature. So pressurize with nitrogen and get your soap bubbles out!

 

I believe as you are in europe the regulation you that covers your question is EN 378.

http://www.feta.co.uk/uploaded_images/files/BRA CodeofP- LeakTightness.pdf

There are two tests to be done, a strenght test and a leak test. The strenght test is i believe 1.1 to 1.3 times the maximum working pressure of the system. This strenght test can be around 800psi on a R410A system depending on what the high pressure switch is designed to stop the system at.

A leak tightness test is i think equal to or above the maximum working pressure, (but not above 1.3 times)


But in practice if you do this the nitrogen will leak by the service valves and into the outdoor unit causing you a lot of problems. So what i would do is either strenght test and leak test the pipework and indoor units before you connect to the outdoor unit (which is what we do on vrf systems) then connect and leak check the connections.
On a small split system such as the ones in your picture i would look up the pressure of the refrigerant for the temperature ona pt chart (or phone app) of the day you are working and test to just below that to prevent the nitrogen getting past the service valves if the leak, i have had this happen a few times.

e.g. Its 20C today so thats a 195psi for R410A, so i would test to 180psi nitrogen and check for leaks etc, if you are leaving the nitrogen in overnight then you would need to take account of cooler temperatures. If it was 15C that would be 167psi R410A so maybe 155psi test pressure.

 

Hi

Thanks for that! A few questions: A few installers have said that I shouldn't go above 20 Bar when pressure testing, even though the refrigerants can be over 30 Bar when it's heating. I don't recall being given any reasons why it's dangerous to go over 20 Bar. Is there something that can get damaged if there is as high nitrogen pressure as what the 410a reaches in action?

And also, what kind of problems can the nitrogen cause in the outside unit? Under normal install conditions I do only test the lineset (I guess by that you mean everything apart from the outside unit?), then I release the 410a. But just the other day I came to a machine that had leaked all its contents and I pressure tested it to find that the inside unit leaks - I could hear it clearly. But at that time, because the stuff was all gone and I wanted to ascertain where from, I intentionally left the valves open so the outside unit was also under pressure. Can I have done some damage to the outside unit by pressure testing it with N2?

 

in mini-split systems and many multisplit systems you have no any other joints but flare joints, and in such a case you can omit pressure testing as pressure tests serve to test joints, not pipes.

that's where you likely come to recommendation how pressure testing is not neede. vacuuming, however, is always needed as you need to fully dry out your pipes.

 

I understand that pressure testing is more for the joints, as it's not so likely (although not impossible) that the pipes or inside unit is damaged. I guess the pipes could be crushed and have got weakened or something. Anyway, I've been told by many different guys that the most common leak point is the flare joints - either badly made or overtightened. I have also come across some really cheap quality pipe that is harder to make a decent joint on. So that's mainly why I test it, to test my own joints! I use a torque wrench on them, which is fine most of the time but not foolproof; once or twice I have come across flare fittings that got really tight without actually tightening the flare properly and still leaked.

 

nitrogen is an important part of the final product in our trade. in canada our regulations state we must use it during brazing to displace oxygen and lessen the carbon flakes in the system that plug up txv valves and screens for dryers. the more things you do to protect yourself from nussence call backs the better, so my view is test with the nitrogen, 30 minutes saves you a drive back and a shot to the ego that most of us tend to have. always use your micron gauge.

but especially on flare joints they're notorious for leaks, i always pressure test flares, because you cant see the integrity of your flare like you can with a mirror on a brazed joint.

 

and if you start your vaccum with a leak your just introducing more air and taking more time on your vaccum

 

Basically, you pressure test to check for leaks from inside out. Think of a nail in your copper line, as you pull a vacuum the nail sucks in and makes a good seal. As soon as you put pressure on it, it pops out and causes a leak.

 

The Rise of the Microns

Hi again. I'm reviving this thread to ask about experiences with the micron gauge after switching off the vacuum pump. I watched a Yellowjacket instructional video that said it's 'normal' for the microns to start to rise after switching off the pump, but that if it rises fast or gets back up to atmosphere you have a leak. It didn't go any further on the subject though.

Assuming you've pressure tested with nitrogen and are happy that the dial hasn't moved in, say, 30 minutes, how long do you all leave the pump standing to make sure the vacuum stays? How long do you allow for it to settle and 'find its place'? If the digital gauge creeps up really slowly, like the smallest measurement unit (we use mBars) in several minutes, do you literally leave it long enough to know that it's stopped creeping up, even if it takes ages?

Many guys here say they can fit a split system in 4 or 5 hours, start to finish including drilling through the wall. That must mean either they're cutting corners or I'm doing something wrong...

http://www.youtube.com/watch?v=Ya75-FUXmVU