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Community and Q&A

Leaking Minisplit Heads

Tanasi | Posted in GBA Pro Help on

Hi all, We have a Midea mini split mounted on an indoor wall.  Behind this wall is an unconditioned entry hall to a 4 unit building.  The suction lines and drain line run inside the wall aprx 15 feet to an exterior wall where the outside unit is.  It has been leaking water down the wall cavity/wall behind the indoor unit for months.  The drain is completely clear.  We have checked it multiple times.  We took the plastic cover off, and with a flashlight were able to see condensation (a lot) running down the lines (which appeared to be insulated but maybe just wrapped in black tape).  The lines run up from the unit before heading towards the exterior.  Behind the wall unit we see there is a large opening in the drywall…presumably made during the installation.  We have had this unit looked at by 4 reputable hvac companies who can’t seem to get beyond “a clogged drain line” to trouble shoot the real problem.  The freon level is fine.  Could the large opening the drywall behind the unit be part of the problem?  Should we remove the whole unit from the wall and check all the insulation?  Any suggestions?  We are at our wits end.  Thank you!

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  1. Jon_R | | #1

    In addition to making sure the lines are insulated, work on limiting the ability for outside air to reach the lines (ie, plug air leaks).

  2. bertmatter | | #2

    I too have a 9000 Midea btu mini split just installed this past April , it worked fine until we hit the heat wave in June (40 degrees C). Then it started leaking a small dribble down the wall under the inside head unit.
    When the temperature went to a more normal (25-32C) then no problem. I know it's not the condensate line I'm thinking it was so hot and the inside head unit so cold that it formed extre condensation somewhere that missed the drip pan.

    Does yours leak at all temperatures?

  3. GBA Editor
    Kiley Jacques | | #3

    Jon Harrod might be willing troubleshoot your problem. I’ll ask him. In the meantime, read his related article: How to Prevent Condensate Leaks from Ductless Heat Pumps.

  4. Jon_Harrod | | #4

    Here are a couple things I would check; you may be able to investigate with a borescope before actually removing the unit.

    --Check that both the larger and smaller copper lines are thoroughly insulated. On most minisplits, the smaller line is not a "liquid line" like it would be on a conventional AC; it is an "expansion line"--meaning it is downstream of the metering device and carries cold refrigerant. Make sure the flare fittings are thoroughly insulated; these usually need to be wrapped in a foam tape. Also make sure that any rips in the insulation are repaired. Insulation should be at least 1/2" thick.

    --Depending on your climate, you may also get condensation on the outside of the drain line, which carries cold water. If so, this needs to be insulated.

    --Seal any connections that allow humid air from the entryway into the wall cavity. This is one of the reasons I recommend wall sleeves on exterior wall penetrations:

    --Double-check the basics: drain pan level, filters, fan and coils clean, fan speed set to medium or high

    --Just to cover all bases, check that none of the fittings on the condensate line are leaking.

  5. walta100 | | #5

    It seems to me the water could be leaking from the drain or condensing on the copper tubes and running down the lines.

    After the unit has been off for an hour pore about a gallon of water into the drain pan of the indoor unit over about 15 minutes the water should all exit the drain tube outdoors. Note the drain line on some units is made of very thin blow molded plastic a lightly rubbing the line across a sharp edge can make pin holes that are almost impossible to see. I only found the leaks by filling the tube with water and blowing into the tube. The pressure turned the dribbles into streams of water.


  6. Tanasi | | #6

    Thank you to everyone who responded! We had the company who installed the unit come out and it was the insulation around the lines. It was loose and untaped. Water was condensing on the lines and dripping behind the unit down the drywall. Hope this fixes the problem!

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