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Mitsibishi Smart Multi 48K Hyperheat cooling issues

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GreatExpectations
GreatExpectations Member Posts: 1
in THE MAIN WALL

Hello,

My system was installed in 2025, and hasn't performed as well as I expected. Originally, we would install 5 window units seasonally. The main living space had 2 x 9900 BTU windows AC units and never had issues keeping the space comfortable. Now the same space has a 15K and 18K wall units and on hot days, the temperature creeps up through the day.

I was at my wits end, so I bought the diagnostic monitor tool and am running the .net software for some realtime data on how the system is running.

First concern, my system is comprised of a 5 port branch box and 5 indoor units (6,6,12,15,18). The 6, 6, and 12 product codes in the software are correct, but the 15 and 18 k units product codes are 9. I'm concerned that the outdoor unit is treating these two larger wall units as 9k units instead of 15 and 18. Has anyone every seen an issue like this? Or is this really not an issue?

Thanks

Comments

  • Ironman
    Ironman Member Posts: 7,933

    Every indoor unit has to be properly addressed at the branch box when installed. It sounds like that may not have been done.

    Also, the refrigerant charge has to be properly calculated and usually a substantial amount added to the system. The calculation process is usually more than what the average technician can handle, but the distributor can do it with the Mitsubishi Diamond System Builder program if given the correct info.

    I’d recommend that you find a Mitsubishi dealer who can do these and correct any other issues that may be there.

    Please also understand that the only way to get the charge right is to weigh it in based upon the correct calculation. And also be aware that on a multi zone system, you don’t get the full rated output of any individual indoor head. The Diamond System program can determine the actual available output depending upon line set lengths and other connected units.

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Kaos
    Kaos Member Posts: 938

    Those two living room units should be able to run at full ouput if properly set up and configured. Usually strange operation with a multi split is insufficient refrigerant. As stated earlier, this is not easy to calculate and not something the installer can guess.

    It is also possible for the installer to miswire the branch box connecting the wiring from the indoor head to the wrong port. This can also create strange operation.

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