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Bryan explains how to detect line set leaks and do a line isolation test in 9 steps. If you’re struggling to find a leak in a split system’s line set, you may consider performing a line isolation test as a last resort.
As we experience more and more copper corrosion and pinhole leaks in ductless line sets, thorough leak detection and line isolation tests will become even more valuable procedures.
First, you’ll want to perform a thorough leak check on the system. You may check for leaks with a pressure test. If there is refrigerant in the system, you will want to check for leaks with a quality electronic leak detector, such as the Bacharach H-10 ( or Fieldpiece DR82 ( No matter which leak detector you choose, use it slowly and maintain it properly.
You can run a heat pump in heat mode to increase pressure in the evaporator and make leak detection easier. Run the leak detector into the chase to check for leaks there. If you still can’t find a leak, then it may be time for a line isolation test.
Before doing the line isolation test, you’ll pump down the system by closing both service valves at the condenser. Crack the suction valve open about two turns. Make sure the system runs in cooling mode, and watch for the gauge pressure to drop about 10 PSI. Remember, you want to pump down as best as you can to avoid dealing with the possible cross-contamination of recovery. Tighten the suction line and pull the disconnect once you’ve finished.
Before you can install a service port on the liquid line side of the evaporator, you must isolate the evaporator. Then, you cut the copper line and pinch it off. If you install a Schrader core, you can pressurize the line set and the evaporator coil.
When you do your pressure test on the lines and evaporator coil, you should use nitrogen in accordance with the low-side pressure test protocol. Watch over the system and note any pressure drops over at least an hour. (We recommend using Fieldpiece Job Link probes: While the system is under pressure, go back into the condenser with a leak detector and check it once more.
Once you find and fix the leak, it’s a good idea to identify the source of corrosion and develop measures to avoid letting the issue happen again. Then, you can release your nitrogen and begin closing up the system. Reattach the copper lines to the evaporator and change out your liquid line drier.
After you’ve put everything back in order, perform one more pressure test. Use a bubble solution to check your braze joints, too. We recommend using Big Blu from Refrigeration Technologies ( Once all of those have been taken care of, pull your vacuum below 500 microns to perform a decay test. Then, you can open the system for service by opening the suction side valve and then the liquid side valve. You would perform many of these final procedures on new installs as well.
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Hey thanks for watching in this video we're going to look at a line, isolation test. This is something that you would do on a split system when you're really struggling finding a leak, and you think that the leak might be occurring in the line set now keep in mind. You do not want to be wrong about this. You don't want to tell somebody that they need to do a line, isolation test when in turn it's something that you could have found by doing a more thorough leak detection.

So a lot of this process is going to focus on just making sure you get that part right, but sometimes you will have leaks in the line set, especially nowadays we're seeing a lot of the ductless line. Sets there's some sort of reaction going on between the copper and the insulation, some people think or maybe it's just the quality of the copper. But we are starting to see leaks occurring in line sets there or you could have a line set. Maybe if it's going underground for a portion, there might be something in the in the ground.

That's reacting with the copper, so it can certainly happen that line sets can leak. This process helps you prove whether or not that's the case, but as always make sure that you're doing things in the right order, so that you're not wasting time and so that you're not wasting your customers money step. One do leak check on the entire system to confirm. No leaks are present everywhere that you can get to.

You need to do a proper leak detection. This means that you have to carefully and slowly go through the system. If you have a system that had an enormous leak in it, that would be primarily done with a pressure test and you know just kind of listen. That would be the first step, but if you've got a small leak on a system, that's got refrigerant in it.

Maybe it's been recharged once or whatever the case may be. You go through and do an electronic leak detection and we suggest good quality leak, detectors we're showing a field piece leak detector here. The h10 from baccarat is a really good leak. Detector.

The stratus from inficon is one that we use and then we've been experimenting with ultrasonic leak. Detectors too. Those all can work really well, but you have to make sure you use them. You use them slowly, you're, not getting interference from other chemicals you're, not bumping them around you're, not sucking any water into the tips, and you also need to know how to maintain your leak detector properly, to ensure that it is working many times.

This step is what leads to people calling for a line, isolation test just because their leak detector is not working. If your elite detector's not working, then you need to know how to test it and maintain it rather than just saying some version of well. I think my leak detector's not working. You know you got to make sure that it is.

If you have a heat pump system, you can run the system in heat mode to increase pressure in the evaporator coil. In order to have maybe some smaller leaks show up. In many cases, obviously evaporative oils do tend to leak, because it is a corrosive environment. You have more water there, and so you tend to get more galvanic corrosion that occurs because of the presence of water.

If you are trying to prove whether or not an evaporator has a leak - and it may be very small - running a heat pump in heat mode for a little bit can can help don't ever over pressurize systems, because then you could actually cause a leak rather than Just finding the leak once you know that you cannot find the leak either outside or inside you don't have any signs of oil. You can't find anything obvious you haven't, you know, maybe you've done bubble tests and your caps and cores and everything else make sure to do all of that. First, if you still can't find anything now we're going to go into the stage of doing our line. Isolation now this is something that you need to do in accordance with your company's policies.

It's often something you're going to need to quote the customer, for so only do it if you absolutely cannot find the leak otherwise, and you have reason to believe that it could be in the line set. Also, you know in our market we have a lot of underground line. Sets so it'd be a good time to go ahead and dig up the chase on the outside and see if there's anywhere in between that condenser and the chase that it might be. So next you pump down the system.

Now you pump it down as best you can. A lot of compressors nowadays don't allow you to pump down to a real, deep vacuum, but it's still helpful because that way, you're trapping as much of the refrigerant in the condenser. As you can so that you're not potentially cross-contaminating that refrigerant by putting it into a recovery tank, many of us like to believe our recovery tanks are completely clean, but that's actually not the case. Generally.

They actually come with a lot of sludge in them. In many cases, so i prefer to try to pump down as much as we can and then you shut down both valves recover any residual. That's left, then you isolate the lines by cutting them near the evaporator coil and then pinching them off. I like to actually pinch off both sides and put a schrader core in the side on the evaporator side so that you can pressurize at this point the line set uh each line individually, and then you can also pressurize the evaporator coil.

Now you can pressure test both the refrigerant lines and the evaporator coil. I say you know to 300. Psi is what i say in this guide, but you have to follow on the evaporator coil. At least you got to follow the low side pressure test protocol on the high side.

You could actually go up to generally, you know even as high as 500 psi now, because you're only pressurizing your line set, you don't want to go really any higher than that, because you run the risk of actually pushing nitrogen through your service valves and contaminating your Refrigerant in the condenser, but you know 300 - is kind of a happy medium you're not going to ruin anything with 300 psi, and so that's why i listed here. But you know, as always, follow your manufacturer's guidelines on that. You do not want to over pressurize an evaporator coil and cause a leak when you are doing this pressure test again: you're separately testing the line set and the evaporator coil, and with this test you want to monitor it with a really fine instrument. This is where probes come in, really handy.

If you use something like your field piece, jawblink probes, it works nice because you can actually watch pressure drop over time. That's what we call delta p or change in pressure. You can use one probe on each and monitor those carefully now, while the system is under pressure, now would be a good time to go ahead into that condenser because it still has refrigerant in it and do a really thorough leak check inside that condenser just check Everything i mean you got nothing else to do anyway, while you're waiting on the pressure test. A lot of people ask how long well, you have to hold it long enough until you can figure out where the leak is at this point.

At this point, you've already done a lot of leak detection, so just keep letting it hold until you know where the leak is and continuing to leak detect inside the condenser is a really good thing to do at this point, you can also go ahead and clean. Your drain, you can do you know whatever else needs doing now, is a good time to go ahead and do it maintenance wise, while you're waiting to see that pressure drop at this point, once you find the leak you got ta rectify it. So obviously you know if it's an evaporator, coil or a condenser coil, something significant. Then that's going to have to be quoted in some cases you're going to find that it is the line set.

If it is the line set, then you're going to have to quote generally to rerun it, but i also like to try to figure out exactly where it occurred if possible. In florida we have a lot of underground lines. So the only way you're going to know is once you pull it out, but in many cases you can kind of figure out what caused it in our market. In many cases, it's because there's a pool nearby and maybe that pool water is running into the chase or maybe it's a water, softener and the salt water is running into the chase.

So it's always trying to figure out what the source of corrosion is. So that way, you don't just run the copper back in the same place. It was in before and then you're just gon na have this same issue all over again once you rectify it. Obviously, while you are brazing, you need to be flowing nitrogen.

You need to put a new filter dryer in some cases, that's going to mean cutting out the old one inside the condenser and of course, in that case, you probably should have done that before you bump down into the condenser, probably should have just recovered, but that's Something i could have mentioned at the beginning, but you do only want to have one liquid line dryer in in the line and i'll generally like to locate it inside near the indoor metering device in the liquid line, if at all possible, to prevent corrosion once you've Rectified the leak, whether that's running a new line set or fixing now go ahead and pressure test. Do another pressure test and bubble test. All of your joints, pull a vacuum down below 500 microns and then open the system for service. So those are all kind of your standard practices that you would do on a new install anyway line dryer bubble, testing pressure, testing, evacuation.

Those are all things you got to do just as regular course. Most importantly, here, though, is having a leak detector. You trust and knowing that you could not find the leaks before you go into the line, isolation test and then at that point the line. Isolation test is going to essentially prove that it is the lines that are leaking again.

The reason why this matters is because, in many cases replacing your refrigerant lines is an expensive, time-consuming, endeavor, and you need to make 100 sure that that's what it is, and that is what this line isolation test allows you to do, allows you to prove it and Then also just kind of allows you to prove that you don't also have a small leak in the evaporator. Coil that got missed just helps, helps prove that again, a lot of people ask how long the pressure test long enough in order to know i'm generally speaking, you're going to want to let it sit about an hour or plus um, to be sure that you only Have a leak in the lines or only in the evaporator coil before you proceed at this point, you do not want to get it wrong all right, thanks for watching. That is how to do a line. Isolation test, maybe some slight variations in your process.

If you have a different process, i'm always happy to hear it. You can go to hvacr, leave me a comment there and let me know what you think thanks for watching our video, if you enjoyed it and got something out of it, if you wouldn't mind hitting the thumbs up button to like the video subscribe to the Channel and click the notifications bell to be notified when new videos come out. Hvac school is far more than a youtube channel. You can find out more by going to, which is our website and hub for all of our content, including tech tips, videos, podcasts and so much more.

You can also subscribe to the podcast on any podcast app of your choosing. You can also join our facebook group if you want to weigh in on the conversation yourself thanks again for watching you.

29 thoughts on “How to line isolation test an ac system”
  1. Avataaar/Circle Created with python_avatars Frank Roper says:

    I like the big blu leak detector. I have only had any luck with the electronic leak detectors indoors on small units since any wind at all makes them unreliable. Bubble soap don't lie!

  2. Avataaar/Circle Created with python_avatars Damon Price says:

    I realize I'm late watching this one, but would like to add a pro tip about it. In the event your isolation test is 24 hours or more, record the ambient temp. 300 PSI on 95 day will not be the same on a 75 day. Use the formula for gas laws P2= T2 (P1/T1) Are you in Barrhaven ?

  3. Avataaar/Circle Created with python_avatars KA DIY👬PINOYKOR👬 says:

    MMLSO thanks for sharing this video and keep vlogging.

  4. Avataaar/Circle Created with python_avatars Afif Jebara says:

    Bryan, you are truly an amazing teacher, and your generosity in sharing this knowledge with anyone interested in this field speaks volumes about your character. Thank you for remarkable contributions. One thing for sure, we are learning from someone who has mastered the theory snd practice in this field. I rarely make comments, but I find you so compelling that I had to write this one. Best wishes!

  5. Avataaar/Circle Created with python_avatars Michael Taurus says:

    thats alot of work for a bad TXV 😉

  6. Avataaar/Circle Created with python_avatars Lauren Leichtnam says:

    Fujitsu says 600 psi pressure test for mini split heat pump. Are you in Kanata ?

  7. Avataaar/Circle Created with python_avatars 洪人元 says:

    Thank you for sharing.

  8. Avataaar/Circle Created with python_avatars Robert Miller says:

    Or a drywall screw in a suction line. Service area Ottawa??

  9. Avataaar/Circle Created with python_avatars Brian Mcdermott says:

    Great info. Keep it coming. Thanks Bryan.

  10. Avataaar/Circle Created with python_avatars timrob0420 says:

    Sometimes with really small leaks I put it under an isolation test like that and come back in a few days to check. I’ve seen leaks as small as 20psig in one week using the nitrogen pressure temperature calculation.

  11. Avataaar/Circle Created with python_avatars Donnie Robertson says:

    Nice job and video

  12. Avataaar/Circle Created with python_avatars Randy Bennett says:

    I use a test gauge that I use for my gas pressure tests. It shows increments of ten for one pound and shows the slightest leak with just 10-15 psi. Also using a mixture of Dawn soap and water in a spray bottle works better then the Blu spray, the bubbles are larger and easier to identify.

  13. Avataaar/Circle Created with python_avatars Sean O'Neil says:

    Learned as always watching your videos. I'm fortunate that most of the linesets I encounter are run through a chase (through attic & down side of home) Get calls sometimes & system out of refrigerant (usually on a weekend) I always ask customers have you hung any pictures or blinds recently? Sure enough they sat yes & ask where & just flow nitrogen & unscrew what they screwed in & leak found. Just a reminder that the best tools we own are our eyes,ears,nose & mouths. Ask the right?'s & a lot of times will save time on not only chasing leaks. I also once found a line set leak in a wall that had a burnt staple next to l

  14. Avataaar/Circle Created with python_avatars Waylon Wells says:


  15. Avataaar/Circle Created with python_avatars 77kthomas says:

    Super tech here: Heat pumps you can remove the charge isolate the condenser connect to the tru suction and tru liquid and perform a pressures test there

  16. Avataaar/Circle Created with python_avatars RC Bronco says:

    In my opinion ,I think the manufacturers quality control sucks. I own AC unit that is over 25 years with no problems (knock on wood) but the stuff they make now is crap. Service area Orleans??

  17. Avataaar/Circle Created with python_avatars richard19 says:

    Step # 1 is make sure you ACTUALLY have a leak rather than a refrigerant flow issue

  18. Avataaar/Circle Created with python_avatars B Morta says:

    Seems like a very long process and expensive for the client. Why not remove all the refrigerant then charge the system with nitrogen/hydrogen with electronic gauge connected. Easiest way to see if the system had a leak then can use a leak detector which senses the hydrogen.
    If its a big system you can break it down and cap off pipework then test the exterior unit individually etc.
    Potentially a big waste of time searching for a leak on a heat exchanger where there might not even be one or its too small to easily detect.

  19. Avataaar/Circle Created with python_avatars JR Apple fan says:

    Suggestions for future videos:
    Wines cooler are made different. It keeps the humidity. How come ?
    2) Portable humidifier. How it is working ? Is it normal that it freeze?
    3) Can you mix the refregerants ?
    Thanks for your great works.

  20. Avataaar/Circle Created with python_avatars Randy Ball says:

    I like to watch your videos I'm always willing to learn plus this helps to sharpin my knowledge in the hvac field I know there is always something to learn education never stops here but I enjoy it.

  21. Avataaar/Circle Created with python_avatars marty maness says:

    My least favorite part of the job is leak checking.

  22. Avataaar/Circle Created with python_avatars ciscojr8ify says:

    H10 Pro is my leak detector. Works great

  23. Avataaar/Circle Created with python_avatars Joe Shearer says:

    I don't know if United still does the National refrigerant one shot recovery tank but that is a good option if you are worried about contaminated reusable cylinder. Basically it's a brand new disposable cylinder

  24. Avataaar/Circle Created with python_avatars Gary Winters says:

    My company has been getting many copper evap coil leaks at circuit elbows,or just inside the end plate of a circuit. The plate rusts around the tube and somehow breeches the copper or aluminum tubes.. what boggles the brain, is there were no leaks at start up.
    Sometimes I wonder if these coils been retagged from older specs?

  25. Avataaar/Circle Created with python_avatars Eassyheat/ Cooling says:

    All this also depends on the age of the system.
    Stay safe.
    Retired (werk'n) keyboard super tech. Wear your safety glasses.

  26. Avataaar/Circle Created with python_avatars Nathan Hurst says:

    I really don’t like telling people we’re going to have to do an isolation test. Try my dangdest to find with other means first.

  27. Avataaar/Circle Created with python_avatars noufal kilayil says:

    Accutrack ultrasonic leak detector is the best

  28. Avataaar/Circle Created with python_avatars t lech says:

    24 hours 600 psi by my equipment manufacturer specifications
    Or until the leak is found first easily

  29. Avataaar/Circle Created with python_avatars HVAC RESIDENTIAL BASICS says:

    We do a 24hr test

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