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Mitsubishi Split Refrigerant Line Sweating Water?

NJHomeownerNJHomeowner Member Posts: 61
I have multiple Mitsubishi mini splits that were installed throughout my house. Yesterday we discovered a leak in my stairwell which as you can see caused damage to the ceiling. I believe the leak has been there since at least Friday. My roof is also new but initially thought this was the issue. My roofer was here this morning but could find no evidence of any leak going into my house for the roof or my siding. There are however water stains (can’t tell how old they are) directly below one of my splits refrigerant lines where it was zip tied and this is directly above where the ceiling had the leak. The drain line went on a separate run directly out of my house and so it’s not possible this caused the leak. The refrigerant line is bone dry right now but it has been very hot and humid here the last few days and this is an unconditioned west facing location on the 3rd floor. I also checked a refrigerant line for a different unit that’s outside and it’s wet like a sponge when touching the insulation (last picture).

Is it possible the refrigerant line is the cause of the leak? If it is, what is the best fix? Is this the right kind of insulation for the piping and if now what should be used?

Thanks for your help.


  • NJHomeownerNJHomeowner Member Posts: 61
    Think I just answered my question on the refrigerant line. I have another in my attic on the east side of my home and this one as you can see is slightly leaking through where it’s zipped tied in one location.

    What is the best way to fix this? Is this the wrong insulation for an uconditioned space and if it is, what should be used? Also these lines clearly should not be zip should they be connected?
  • ratioratio Member Posts: 2,489
    Both lines on a mini split are going to be below the dew point during cooling operation (means they're going to be cold & sweating). They must be insulated, with no gaps in the insulation, for the entire length.

    Zip ties on any lineset insulation are a mark of non-professionalism, for the obvious reason seen in the picture—they compress the insulation & can even rip it if pulled too tight.

    The quickest fix would be to wrap several layers of foam insulating tape around the zip ties, along with any gaps or holes in the insulation. If I absolutely have to tie something on to a lineset, I use this, being sure to cut the tape into pieces so that it can be easily applied without stretching it.

    Runs through non-conditioned spaces may require more insulation than is provided from a standard mini split lineset. As long as both lines are individually insulated, some of this around both lines would probably work adequately.

    The fact that you've got damage to your house should get the installer out there pretty quickly to fix the problem.

  • JUGHNEJUGHNE Member Posts: 6,972
    Usually the insulation is supplied covering both copper tubes as a line set.
    If insulated on site then 6' lengths are slipped over the copper lines and the butt joints would be taped.
    Both lines must be insulated with no gaps or openings that will cause the attic humidity to condensate on the cold lines and drip.
  • NJHomeownerNJHomeowner Member Posts: 61
    edited July 2019
    Thanks to both of you on the response. Believe they used the insulation that same with the pipes. What type insulation should be used if I’m in an area where the attic can get well above 100 degrees in the summer and below freezing in the winter?

    Assuming any insulation on the exterior of my home should be replaced too? Believe they would have used these pipes which had 1/2” insulation on it:
  • ratioratio Member Posts: 2,489
    ½" Armaflex insulation is more than adequate. If you're concerned about it passing through an unheated space, more insulation could be added. Like I mentioned before, you could add additional insulation around the lineset as a whole.

    If water is dripping/leaking from the lineset, it's a gap in the insulation that's causing it. Warm moist air is coming in contact with the cold pipes & condensing water, exactly like what happens in the evaporator (inside part). The water is running down the lines to a low point & dripping out. The holes in the insulation must be located & repaired.

  • NJHomeownerNJHomeowner Member Posts: 61
    Thanks. If they use an insulation tape over all the spots where it ripped (basically every one to two feet where the lines were either clamped or zip tied for all 8 units) this will hold up over time? The adhesion won’t deteriorate from the heat and humidity in summer and cold in winter?
  • ratioratio Member Posts: 2,489
    If the Armafles is clean when the tape is applied, it should stay stuck. It should be repaired any place you can see copper or reasonably think copper may be exposed to the air. Gouges that don't penetrate the Armaflex should be ok.

    To get enough water to damage the drywall like that indicates a rather large condensate leak (large gap in the insulation), most small tears won't produce that much water. How sure are you that the condensate drain itself (pr possibly a different one) doesn't run along that lineset?

  • NJHomeownerNJHomeowner Member Posts: 61
    edited July 2019
    I’m positive on the drain line. There are none in my attic. This units drain line goes straight outside and down a line hide. All other lines go through the attic before going down to the condenser it’s connected to in the other side of my house.

    It has been 100+ degrees here since Friday and really humid for days before. The line that caused this damaged is also in the west facing space of my attic and unconditioned so has to be the hottest place in my house. When we first checked the line yesterday morning it was not leaking but by the afternoon it was. Guess it must have been leaking all summer and this was the cumulative result from the hot humid weather we have been getting?
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 7,091
    Wrap with armaflex tape. You could use some duct tape (they make Black duct tape) where the armaflex tape ends to secure it from unwrapping
  • NJHomeownerNJHomeowner Member Posts: 61
    Thanks. And this will hold up indefinitely? I ask as I had a separate issue where they duck taped the drain line to the main one and it fell off. This was sitting in a line hide on the exterior of my home, but it also happened only 9 months after installed.
  • pecmsgpecmsg Member Posts: 1,450
    If it’s ripped that bad and water logged replace it.
  • NJHomeownerNJHomeowner Member Posts: 61
    Guy there now. Said he found about a 3 inch section with exposed copper pipe which was above where the damage to ceiling occurred. Said he wrapped it with armaflex along with a tape on top of it. Also for that line he removed all zip ties and clamps and did the same thing.
  • ratioratio Member Posts: 2,489
    Sounds like they found the problem.
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