GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Ductless minisplit failures

CARL SEVILLE | Posted in Mechanicals on

I have had 2 indoor coils fail in my Mitsubishi ductless heads within 3 years of installation.  On top of that it takes the HVAC contractor more than a week to get the replacement part.  Anyone have any similar experiences?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. ERIC WHETZEL | | #1

    Our Mitsubishi ductless system is about 2.5 years old. Apart from the interior distribution heads needing a deep clean soon, no issues so far.

    Are you using one of their 'diamond' installers/contractors?

  2. Expert Member
    CARL SEVILLE | | #2

    Yes, the initial installer actually screwed up some things although nothing that should have caused the failures. My new company is also a Diamond contractor. I'm concerned about 2 out of 3 units failing so soon. I have older models in another house without the same problems.

  3. walta100 | | #3

    How sure you are the leaks were in the coils? Finding small leaks can be very default, frustrating and consume lots of time. All too often someone will just throw in a coil instead of locating and fixing the leaks. I am skeptic unless they show you the soap bubbles.

    Were the 2 bad coils attached the same compressor?


  4. Expert Member
    CARL SEVILLE | | #4

    Different compressors. Mechanic used a sniffer and found the leak in the coil. I was there when he found it on the 2nd one. Wasn't there for the first.

  5. Expert Member
    Akos | | #5

    I call BS on leaky indoor coils. Unless somebody put a screw though the coil, there is no way that will leak.

    Leaky flare, which would also show as a leaky coil since it is in the same area, definately happens. I've notice that most installers won't do a proper pressure test and you end up with the refrigerant escaping in a couple of years.

    Whatever work they do, insist on doing a proper pressure test at 300psi, snoop all fittings and show you the system holding pressure after a couple of hours. Without this, there is no way to find the small leaks and you'll end up with needing these kinds of "repairs".

  6. user-2069108 | | #6

    My Mitsubishi indoor unit failed in about 1 1/2 years. The coil had at least 3 leaks. So, the warranty kicked in and I was sent a new coil. My HVAC guy and I spent about six hours taking apart the indoor unit and putting it back together. It was ridiculous. Everything had to come out of the indoor unit to get full access to the coil.
    The resulting cost was ridiculous too (and he did not charge me what he would have had I been "just another call out").
    It would have been less expensive to buy another indoor unit.
    I wrote to the company twice complaining about the product and received absolutely no response. As you may assume, I am not happy with the company and would recommend that people look into other brands.
    This was less than a year ago, and so far it is working well.

    There were lots of bubbles as he charges it with nitrogen.

  7. AddisonHomes | | #7


    So glad to find this post of yours. I have a Mitsubishi City Multi multisplit VRF system that I had installed in a remodel and energy upgrade of my 1970s home 10 years ago. The system had one condenser/compressor outdoor unit and three ducted air handlers inside. First issue came 1 year after install. A coil leak. Replaced the coil under warranty. A year later, another coil leak. This time, the coil wasn't available so we had to replace the entire air handler, fortunately, under warranty. After another 18 months, the third coil leaked and had to be replaced. So, within 3-1/2 years, all 3 coils had been replaced due to coil leaks.
    The story continues - in year 5, the compressor failed and I had to replace the condenser/compressor - covered under warranty. In year 7 and 8, two more coils had to be replaced due to coil leaks.
    And then a little over a year ago, in year 10, two more coils leaked and I just shut down the system.

    The installing contractor was an expert to the experts. He actually was one of Mitsubishi's "go-to" warranty support contractors for commercial VRF systems. I know that he designed and installed my system correctly. At each coil failure/replacement, he worked to isolate the system, purged and high-pressure tested the system with Nitrogen to ensure that no other leaks existed.
    I worked directly with Mitsubishi to try to get a solution for replacing my entire system as it seemed as though I had a lemon. Despite much discussion and conversation, the discussion essentially ended when I answered one question - that question, "Does your house have spray foam insulation?" I did retrofit my cape cod home with open cell spray foam on the underside of the roof deck. I also added an ERV for ventilation. The folks at Mitsubishi said that they had had some coil failures in homes with spray foam insulation, but when I asked questions about what specific chemicals in the spray foam they found to result in coil corrosion, they didn't have any specific chemicals that had been associated with coil failures.
    I'm definitely interested in anything that you learn or other ideas for possible causes for such failures in relatively new systems!

  8. Expert Member
    CARL SEVILLE | | #8

    Todd - I heard some of the same questions about spray foam. My house doesn't have any, so it can't be blamed on that. I'll keep you posted on anything I hear from them.

    1. JC72 | | #11

      Hopefully you'll get it sorted out. Keep in mind there's always the option of driving up to the Mitsubishi Electric Trane plant in Suwanee Ga staking out a protest across the street with a large banner about their poorly made coils. ;)

  9. user-2069108 | | #9

    That spray foam excuse sounds like BS.
    All evaporators have an aluminium coil, whether it is a mini split or an AC system. If using a bit of spray foam in a house could cause coils to fail, we would have heard about it a long time ago.
    The problem is not spray foam. It is poor quality control.
    Todd, you must have paid a fortune for repairs since Mitsubishi only covers the parts under warranted. If mine fails again soon, it is going to be removed, and another brand us going in.
    Just to be certain, I recognize that only folks that have had problems are likely to post here, but It is good to hear that not everyone is happy - even if we are a small minority.

  10. CramerSilkworth | | #10

    Formicary (aka "ant nest") corrosion is known to attack AC coils. Could be some VOC in a building product, but it's hard to nail down. Google it - it's fairly well documented (but not widely known by many) in the HVAC industry, including ACCA, Carrier, and other groups.

  11. burninate | | #12

    Why would it attack these AC coils and not typical central air heat pump coils? What's different between the two?

    1. CramerSilkworth | | #13

      It attacks both.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |