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Leak at mini split

So I’m officially outta my mind.  Installed a 4 zone mini to completion.  Pressure tested, evacuated & commissioned.   Even got a call in August during heat wave saying how happy they were with the well performing system.   (I love those calls!).   Now10 weeks later…. System fully depleted.  Pressure tested with dry nitrogen & isolated condenser.  Leak is out in load, (heads or piping).  Losses about 10 psi per day.   Mfg. Tech rep had me put r410a in (1 lb.) then back it up with nitrogen & use electronic leak detector.  Nothing!  Removed all covers & ‘scanned’ all coils & u-bends.  All our flared connections have integrity.  Thinking piping?  Maybe isolate & pressure test each individual head…?   Any thoughts?  


  • clammy
    clammy Member Posts: 3,092
    If you can’t seem to find using the standard methods then your last ditch effort would be as you suggest . Purchase some flare plugs for by the indoor unit and pressure test from condenser if no leaks then indoor unit by indoor unit . Have you tried using a ultra sound leak detection , I ve heard that some have had great results using this method ,personally I haven’t yet brought one but did purchase a Bacharach h10and even though pin pointing is always tough for ambient refregerant to narrow it down its better then a few other units I have owned . Personally w a h10 you should be able to tell when entering a room w a leaky head that there refrigerant present . Mini split leaks can be quite tough and a pair of good eyes ,time and patience's are definitely required . Also a good leak bubble solution not home made soapy water makes the job easier . On mini splits I tend to leave pressurized w nitrogen as long as I can and check all joints multi times ,also on leak tests I use my digital gauges easier to see any pressure drop and even though I get no drop in pressure I will still spray every flare and stare at it for a eternity to be sure ,sometimes a leak is so small that you don’t pick it up until 6 months or so later when she’s just about flat . Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • Jamie Hall
    Jamie Hall Member Posts: 22,897
    Minor suggestion, from cars -- not HVAC. Does that unit use Schrader valves on the pressure test/fill/purge ports? If so, replace the innards with new and see if that helps.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mastercraft
    mastercraft Member Posts: 24
    Thank you.  Didn’t think of flare plugs! Was gonna zoom lock process ports on each suction & crimp/braze each liquid line.  Yes, using good fluorescent leak detector (on external joints)  we did install the white insulated linesets w’ the knurled finish.  I’m already 12 hrs. Into this repair which is longer than the original installation!    Appreciate the responses!  
    JUGHNE Member Posts: 11,021
    If you get the leak narrowed down to one lineset/unit, you can further isolate the line set by plugs in the end of the line at the unit.
    Or construct a U bend jumper with flare fittings and the head end of the lineset.

    Then charge each line separately.

    If no discovery there then on to that coil head.
  • mastercraft
    mastercraft Member Posts: 24
    Makes sense as them I can determine whether lines or head.  Thank you!