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Community and Q&A

Musty Smell in New Minisplit in Cool or Dehumidify Modes

SJT3 | Posted in General Questions on

I have some new Mitsubishi mini splits at home.  One of the heads already has a funky smell to it that is usually musty, but on occasion has smelled just like old stinky socks left in a gym bag.  This started a week after it was installed with use in Cool or Dehumidify mode.  I had read that Fan mode should be used to dry the coil after using to Cool or Dehumidify and this is usually done.  Although, doing this increases the measured humidity right back to where it was before starting Dehumidify mode.

This is a low-wall KJ head and the drain was routed to the left hand side to accommodate the desired installation location.  What I can see of the drain hose is sloped appropriately.  Other heads of the same type do not have the odor problem.  It has been very humid since the installation, but I did not expect a smell like this so soon.  It has become overpowering and the room is unpleasant to be in.

It would seem that this in an installation problem.  If not, does anyone have experience with this smell in a new (or older) unit?

Thank you

GBA Prime

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  1. Jon_R | | #1

    A good drying out once every two days should be enough to deactivate mold. IMO, the AC should do this automatically.

  2. Expert Member
    BILL WICHERS | | #2

    Check if you have any nasty backed up condensate in the unit. Stuff can grow in that -- bad stuff. Condensate needs to drain. Drying is usually enough for the coils as Jon mentioned, but it it keeps going or gets worse, there are cleaners made for cleaning the coils. I would avoid using the cleaners until you really have to though.


    1. SJT3 | | #6

      Hi Bill,

      Condensate pan looks clean and the drain runs clear when I pour tap water into the pan. The installer thought that spraying a cleaner on the coil would be the next step.
      Do the cleaners wear at the coil? Or are there other reasons to use the cleaners only if needed?


  3. walta100 | | #3

    Have you seen water draining from this unit’s condensation hose?

    You could put one of these tablets in the drain pan. I think they are mostly copper and stops stuff from growing.


  4. GBA Editor
    Kiley Jacques | | #4

    Jon Harrod has written a few articles about troubleshooting problems with minisplit systems. Above, Bill mentioned the possibility of backed-up condensate, which Jon addresses in this article: How to Prevent Condensate Leaks from Ductless Heat Pumps.

    He says: Issues with sluggish drains and low airflow tend to show up when a system is tackling a high latent load . . . Setting fan speed to “low” in air conditioning mode or setting the system to “dry mode”—which both slows fan speed and lowers coil temperature relative to regular cooling—can lead to condensation on the blower wheel and louvers, especially when latent load is high. Problems of this nature can often be resolved by setting the fan speed to medium or high.

    1. SJT3 | | #7

      Hi Kiley,

      As an editor, do you know why the subject of my question was edited to remove mention of "dirty sock" smell? I thought it was a relevant detail to explain my problem.
      I realize that many contributors to this site are proponents of mini splits for many applications. Is GBA also supported by any mini split manufacturers?

      1. Expert Member
        NICK KEENAN | | #10

        GBA relies on advertising revenue to support this forum. The main driver of advertising revenue is Google. Google prioritizes traffic based on words in the page title. So GBA has someone who edits the titles of posts to words that are seen as more likely to get Google hits and thus clicks and advertising dollars.

        I often disagree with the substitutions they make but it's not my site.

  5. ianrking | | #5

    I also recently had Mits units installed and also noticed a funky smell very soon after install during April (early cooling season). After much to-do I think the smell in our units were because of cooking fumes. If the unit would cut out after we had cooked it reeked like fish! Something about the filters or the coils or something. Early on made the installer come back and check for mold and there was absolutely nothing on the coils or the pan.

    It was very strange and disgusting indeed. Hasn’t smelled for much of summer.

  6. NetzeroinNH | | #8

    We had stinky issue that was isolated to the HRV that served the rooms that had the stink. Turns out that both the condensate pans from the HRV and the attic mounted ducted mini split systems were piped to the plumbing stack. The “p” traps were dry and apparently the HRV running created a negative pressure differential and was pulling air from the plumbing stack. Keeping these p traps filled are now on maintenance check list. This ended the stinky smell. This would only apply if your condensate drains are piped to respective plumbing stacks. The installer had came back and could not figure it out and thought a mouse had died in the ductwork. Being a facility commissioner in my past life, i went through a new HVAC and Plumbing system checklist approach, which included verifying p trap loading where installed. Voila!

  7. jeffd104 | | #9

    I just had a 3 zone Mitsubishi mini split system installed in my home 20 days ago. In one of the units, I noticed a strong vinegar smell coming out with very moist air. This happened after I switched the unit from dry mode to heat mode. Could the condensate line be backed up? Is it not draining properly? I have the technicians coming back out to check. Any ideas on what it could be?

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