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Helping diagnosing serial communication error with Fujitsu mini-split

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Comments

  • mattmia2
    mattmia2 Member Posts: 11,728
    I don't think you needed a meter for that.

    Looks like it is a 10 a 250v fast acting fuse. The next question is what blew it.
  • Sethamin
    Sethamin Member Posts: 60
    edited August 2022
    mattmia2 said:
     The next question is what blew it.
    So around the time that this system stopped working, I had a separate mini split system being installed (Mitsubishi 48k BTU condenser + 3 heads). They were wiring the condenser up on the day the fuse most likely blew. It's on a separate circuit but the same panel. What could they have done to cause this?

    (They of course swore up and down that they couldn't have caused an issue, but the timing is suspicious to say the least)
  • 109A_5
    109A_5 Member Posts: 2,131
    @Sethamin, with the violence that fuse failed with there may be something else wrong with the board or the motor or the wiring. To maintain the manufactures safety features the fuse should ultimately be replaced with the same type and value. The fuse's letter code should be on one of the metal caps, like AGC as the ones in the HD link for example. The same fuse may be available from other vendors besides Fujitsu. To me it looks like a 'Medium Blow' or a 'Slow Blow' fuse. The AGC fuses from HD are fast blow and may not last with motor loads. As a quick test I would probably use the HD fuse.

    Replace the fuse with the safety switch or circuit breaker off.
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • Sethamin
    Sethamin Member Posts: 60
    Replaced the fuse and everything is working again! Except that the compressor sounds a little noisy now. Hope that's not a bad sign ..
    109A_5
  • Illinois_Sam
    Illinois_Sam Member Posts: 5
    Where was this fuse located? Your photo of the wiring diagram, was it in the front cover panel?
  • russyou
    russyou Member Posts: 1

    I just finished reading this thread because I have two Fujitsu AOU36xxxx units with three heads each (2013 installed) and I'm having communication issues starting today. Several years ago I had the same issues with one of my units and it turned out to be a blown fuse in the same location. The fuses are on wires, visible as soon as you open the front panel. Mine fuse blew because the original installers cheaped out and used metal strain relief on the wires coming into the condenser unit and over the years vibration did it's thing and shorted one of the head leads to case. It's a shame the fuses weren't checked first thing. Glad your problem is solved, I'm checking my fuses (on my second unit) tomorrow when it's supposed to be above freezing.

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