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Mitsubishi Mini-split Branch Box question

Residential 5 port Mitsubishi branch box: PAC-MKA51BC

If only 4 of the 5 ports are used, does it matter which ones? The install manual sort of insinuates that you should use A, B, C and D and leave E unused, although it sounds more like a recommendation than a requirement. My installer used A, B, D and E and left C unused, presumably because port E has a 1/2" gas line (the other 4 are 3/8") and one of the inside units was larger and required a 1/2" line. That way, he didn't need to install a 3/8" to 1/2" converter pipe.


  • GWGW Member Posts: 3,766
    Does not matter which ports you use. Does not have to be sequential, at all. But, you have to select the correct addressing for the wiring. Every time I do a D box, too many months have passed and I can’t remember the exact process. It’s buried in my notes somewhere
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • StoliStoli Member Posts: 10
    Cheers Gary. I appreciate you taking the time to respond.
  • Kybeans403Kybeans403 Member Posts: 42
    Thought its 15 and 51 (condenser first then box)
  • StoliStoli Member Posts: 10
    edited July 10
    Probably important to note that there may be differences depending on the models, but in my case, I have a newer MXZ condenser and the PAC-MKA51BC branch box with 4 indoor units hooked up, so the addressing setup is:

    Condenser: 51 (SWU2, SWU1)
    Branch Box:
      Address: 01 (SW12, SW11)
      SW1: Active ports (A, B, D, E) set to ON

    That effectively addresses the indoor units to
    A : 01
    B : 02
    C : (NOT USED)
    D : 03
    E : 04

    Gets a little more complicated with multiple D boxes, but the manuals are pretty good regarding proper addressing setup.

    ** NOTE: I'm not a Mitsubish Tech. **

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