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Mitsubishi h2i over temping rooms

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Hello. I installed a packaged mxz3c30nahz2 with 2 6k and a 18k FH series wall units. The 18k is piped and wired to port A and the others are B and C. For winter if I leave the 18k unit off the other 2 do ok at keeping the room at setpoint. But if I run the 18k unit the other 2 rooms will start to over temp. My kids room was 78 and pumping out heat. Remote has been set to 68 all winter. I’m not sure if the wall mounted thermostats will fix this or I have a issue with the 18k head or outdoor unit. 

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  • pecmsg
    pecmsg Member Posts: 4,880
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    That unit will only ramp down so low, if it cant ramp down low enough it begins feeding the other heads.

    Sounds like the 30 is too large for the home.
  • ratio
    ratio Member Posts: 3,649
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    Also, ISTR that the Mitsubishi (& others) keep the fan on at a low-low speed to keep the in-head temp sensor valid & crack the expansion valve for oil control. The net result is the head heats (or cools). If you're using the wall remote, you can switch the sense point to that & shut the fan off completely when satisfied. See https://forum.heatinghelp.com/discussion/180281/mitsubishi-indoor-outdoor-problem-one-room-never-stops-cooling-problem-solved for some details.
    ChrisC59
  • ChrisC59
    ChrisC59 Member Posts: 1
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    pecmsg said:
    That unit will only ramp down so low, if it cant ramp down low enough it begins feeding the other heads. Sounds like the 30 is too large for the home.
    I would hope it’s not too large. It’s the exact sizing 3 companies came up with. I’ll get exact room sizing tonight. It’s a 1500sqft cape with 2 beds and a bath on the 2nd floor.