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  1. #1
    Join Date
    Sep 2010
    Location
    New England
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    131

    evacuation / leak checking

    ok. curious what you guys think
    typically if i install a new unit and the condenser has a pre- charge (mainly ductless units but guess it could apply to any pre- charged unit) i am a true believer not to pressure test with nitrogen as to not contaminate with non condensables due to valves leaking by or venturi effect.
    in the process now of evacuating several ductless units and using vacuum pump for leak checking
    the way i see it. if after ive reached 500 or less on micron gauge i shut and valve pump off
    if my gauge goes above 1000 after sitting for half hr then i have moisture still in system. if it goes above 5000 then its a leak. usually it withh rise 200 or so microns and stay there
    is this as reliable as puting unit under 200 lb nitrogen pressure

  2. #2
    Join Date
    Jul 2009
    Location
    Columbia, MD
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    4,483
    Sometimes you may find a leak in a vacuum and not under pressure and vice versa. It is rare but, it does happen. I understand your methods and seems like it would work.

    If you leak it shouldnt be much trouble. There is no oil in the lines to saturate with moisture.

    I would take a temp reading of where the unit sits. For example...its 90* at the pre-charged unit and it is using 410a. The pressure in the unit should be 275psi. I would pressure test at 250. This way you assure the nitrogen cant mix with the refrigerant if the valves dont hold.

  3. #3
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    1,918
    If you are concerned about the valves holding the charge in properly in a pre-charged unit (or nitrogen getting in the pre-charged system), then just use your leak checker before you begin brazing up the lines. Check the valves to be sure they are holding.

    Although I've never done that, it would be a real pisser to think you had a leak in your piping when all the while it was a leaky isolation valve.

  4. #4
    Join Date
    Sep 2010
    Location
    New England
    Posts
    131
    basically is this an acceptable way to leak check. i always use nitrogen on dry systems
    it seems most instructions that come with ductless units do not mention nitrogen and recommend vacuum method
    guess we will find out when we start the 5o plus units
    hope this doesnt turn into a nightmare

  5. #5
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    1,918
    Quote Originally Posted by Rane69 View Post
    basically is this an acceptable way to leak check. i always use nitrogen on dry systems
    On another thread dealing specifically with using a micron meter for leak checking, I said the only time it seemed valid to me was on a brand new system, similar to what you have here. And it seems I took some heat for that stance.

    But for me doing emergency service, I would spend untold hours in a day waiting for the vacuum pump to pull down. You essentially get all of the air out pretty quick. Then you are just boiling the refrigerant out of the oil. And that can take a long time.

    Which is why I say that I only use a micron gauge on brand new piping. And you will get fast results. But far and above all else, for leak checking, the H-10 is the gold standard.

  6. #6
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,778
    I always pressure test to ~150psig for 10-20 minutes then pull a vac to at least 500 microns and hold below 1000 for 10 minutes. If you vacuum and have a leak then you are pulling in moisture.

  7. #7
    Join Date
    Sep 2010
    Location
    New England
    Posts
    131
    [QUOTE=jtrammel;19123251]I always pressure test to ~150psig for 10-20 minutes then pull a vac to at least 500 microns and hold below 1000 for 10 minutes. If you vacuum and have a leak then you are pulling in moisture.

    if i had a leak i would fix it thhen evacuate until i reach appropriate micron levels
    the units im dealing with, like most ductless splits pull down quick
    my concern is why the manufacturer recommends this method to leak check and evacuate
    again this is not a typical way i would leak check and evacuate
    i think best is to pipe in air handler, do not connect condenser and pressure test lineset and air handler with nitro
    then make your flares at condenser and evacuate

  8. #8
    Join Date
    Sep 2010
    Location
    New England
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    131
    forgive me but what is "h-10"

  9. #9
    Join Date
    May 2014
    Location
    Bay Area California
    Posts
    1,918
    Quote Originally Posted by Rane69 View Post
    forgive me but what is "h-10"
    It is a leak detector that has been around for decades and is about the best you can get.

    http://www.bacharach-inc.com/h-10g.htm

    Every other leak detector is measured against this one to see how good it is. It will detect something like 1/2 of one ounce per year leak. That's pretty small, or good, depending on how you are looking at things.

    It is perhaps the single first "major" investment for the beginning tech. There is a battery operated version that I have heard works just as well, but I haven't upgraded to that. My first one was a H-10A, now I'm up to a H-10G.

  10. #10
    Join Date
    Sep 2010
    Location
    New England
    Posts
    131
    i have a d-tek. hasnt let me down yet

  11. #11
    Join Date
    Sep 2004
    Location
    Milton Ontario
    Posts
    29
    I don't see how pulling a vacuum could EVER be regarded as an acceptable means of ensuring a system is leak free. Look at the logic... Atmospheric pressure at sea level is 14.7 PSI. If it were physically possible to pull a perfect vacuum, you would only creating a pressure difference of 14.7 PSI. I interpret this as the same as pressure testing at 14.7 PSI.

    Also, all of the components of an A/C or refrigeration system are designed to hold pressure in, not to hold against external pressure.

    Always do a nitrogen pressure test.
    "If you can't deceive someone who trusts you, who CAN you deceive?"

  12. #12
    Join Date
    Jun 2001
    Location
    Northwest Indiana
    Posts
    1,321
    if your cups are filled and ya pull a 300 micron vac your good to go.
    That said, r410A is pretty wicked when the pipes come apart at 400 psig.
    we all purge nitro when brazing so spend the extra 15 min to half hour and be safe.
    If you cant fix it right, try again.

  13. #13
    Join Date
    Sep 2010
    Location
    New England
    Posts
    131
    well out of 50 units ive found three with very tiny leaks micron gauge not able to pull down and hold
    pressure tested with 150 # nitro and had a hard time finding leak
    let nitro go and introduced some 410a then sniffed out and found on flare
    im not saying this is my preferred method of leak checking but after doing so many units i have to say it works

    i think i would only do this on small new systems
    on a large system it would take too long and not be worth it

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