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Community and Q&A

Minisplit Maintenance Costs and Schedule

jameshowison | Posted in General Questions on

What’s a reasonable expectation for how often a mini-split needs to be serviced? And what’s a reasonable cost per unit? How often do units develop noise issues after cleaning?

I’m asking because we’re being told that our units (ceiling mounted Mitsubishi one-way ductless, MLZ) will need to be cleaned very two years or so.  And the cost is ~$400 a unit. We have six units, so that would be $1,200 a year, averaged. Not to mention the hassle of scheduling/accommodating messy cleaning.

We had cooling issues, they inspected the coils and noted lots of dust in them, explaining that causes lowered performance (and hence they were cooling adequately).

Now, all of two weeks later, two of the cleaned units have developed loud buzz noises. The diagnosis is that the sealed motor units need to be replaced. And that happens fairly frequently, which is why the cleaning cost is high … Oh, and it’ll be 10 days until they can be fixed (can’t sleep in the bedroom again …)

I had hoped that the dust issue was to do with un-level ceilings causing by-passing of the filter, something now fixed (by adding ugly weather stripping). But now they are saying that even wall mounted units have a similar schedule and tendency for the motor to need replacing after cleaning …

So I’m looking for some experience here?  Are all units this way? Is it just the MLZ units? Or is this the result of bad installation and/or bad cleaning?

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  1. Expert Member
    AKOS TOTH | | #1

    I have zero experience with ceiling mounts, but will wall mounts used for AC, the blower wheel needs cleaning about every 6 years. This is time consuming work (take apart, remove blower wheel, wash, reinstall) I haven't found a good way of doing this yet.

    Buzzing doesn't sound like bad motor. What usually goes on motors are bearings which will tend to squeal. Buzzing sounds like something was not put back right and vibrating, loose wire that wasn't tied up or somebody bent the blower wheel. I call BS on blowers needing to be replaced right after cleaning, somebody broke something.

    If you can find a better filter in there, it will last longer. I put a standard furnace filter on mine in my bedroom mostly to reduce the air flow, but as a side effect it has been staying significantly cleaner than the other ones.

    1. willymo | | #8

      Akos, are you talking about wall heads? What kind of furnace filter can you put in there?

      Thanks, Bill

      1. Expert Member
        AKOS TOTH | | #10

        I used a large standard Merv 8 furnace filter cut in half. This was gaffer taped to the top of the unit. The size about matches the existing opening on the top. Not the prettiest, since above head height, you can't see it.

  2. jameshowison | | #2

    Akos was right :)

    To follow up here, we finally got the regional rep (wholesaler, I think) to come by, along with the installer and their crew. Spent a day working on the "buzz" issue. Things tried:

    - Re-seating the grommet at the non-motor end (there's plastic in the middle of the rubber that can get turned, ours was misaligned visually but didn't fix it).
    - Replacing the grommet at the non-motor end with a new one.
    - Ensuring the distance between the motor and the plastic fan was same as in a factory unit
    - Replacing the motor entirely (wholesaler had brought a new MLZ for comparisons).

    None of those worked. Brutal to see the effort and the noise unchanged after each attempt. Quiet in the room (ok, there was the buzzing ...)

    Eventually "strategic pushing on the motor end" with a screwdriver established that it was vibration between the housing and the metal frame mount. I believe the solution involved re-seating a rubber isolator for the motor housing and possibly rotating the motor in the housing so nothing contacted the housing. I suspect it's pretty easy to get this housing seating screwed up when jostling around to remove the fan wheel, since it's super tight in the MLZ units. We have two other post-cleaning units to fix still (one of the cleaned units went back together properly and didn't buzz, which was key to comparing).

    Props to mitsu and the installer for sticking with this one and not gas-lighting me about the noise being expected/within spec :) The wholesaler/rep had pushed up through Mitsu global to seek a solution but nothing seemed to be known.

    (note for future searchers: The MLZ units still make too much random noise for use in a bedroom, though.)

    So Akos was right. "something was not put back right and vibrating".

    1. pablov | | #9

      Hey James,

      I own a MLZ unit in my living room. While I am not getting the "buzzing" sound, I am getting a clicking and contracting/expanding noise when the unit has reach the desired temperature and it stops blowing air. Are you getting these noise as well? The noise seem to be more prominent during heating mode.

  3. joshdurston | | #3

    I'm wondering if the units with the fan in front of the coil (think ducted or floor mount) might be less prone to mold build up on the fan. The wall mount units generally draw through the coil which places the fan in the danger zone for mold and getting wet. I have a wall mount and am dreading the eventual cleaning. I'm thinking of laying some filter media on top of the air inlet to hopefully keep the insides a bit cleaner.

    1. bfw577 | | #7

      I have both a floor mount unit and a wall mount. The floor unit is like 10 times easier to take apart and get to the fan to clean. It is also vastly superior in heating mode as it has an outlet out the top and one out the bottom. Here is a picture from when I installed my floor unit of the fan. The black cover comes off easily with 4 Phillips screws to access the fan.

  4. Expert Member
    NICK KEENAN | | #4

    This is one of the things that turned me off when I looked at mini-splits. Most have a very wimpy filter. Dust is the mortal enemy of HVAC systems. And I like having a nice big filter that takes the dust out of the air I breathe. Give me disposable any time.

  5. Expert Member
    AKOS TOTH | | #5

    Good to hear the Mitsubishi came through. It doesn't sound like a big item, but these kinds of issues can make a big difference for the home owner.

    I'm starting a new project and going with ducted units with big filters. Maintenance is a pain, simpler the better, don't want to deal with blower wheels again.

    Before setting on this, I was looking at some of the ceiling units and it looked like some can accept a 1" pleated filter, don't know if they have enough blower power to push enough flow through one though.

    Next time I have to clean a blower wheel, I'm going to try to just blow it clean with an air gun. Taking them out to clean it properly is way too much work.

    1. Expert Member
      NICK KEENAN | | #6

      The problem with using an air gun is all that dust goes right back into the room where it will end up right back on the blower wheel.

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