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Strange behavior of Mitsubishi mini-split with thermostat interface


I recently decided to try to convert my mini-split units over so that I can control them via the same wifi thermostat as the rest of my home. I bought the PAC-US444CN-1 thermostat adapter interface and an Emerson Sensi ST55 wifi thermostat and hooked them up to my Mitsubishi MSZ-FH09NA mini-split according to the instructions (including using a Triad VPL24-210 transformer attached to the power leads to provide power to the 'stat).

I configured the 'stat for 2-stage conventional system, using wires C, R, G, W1, W2, Y1, and Y2 coming from the adapter interface. The only thing that didn't go quite as I expected was that the voltage I measured coming off of the transformer was a little over ~30V rather than 24V, but I checked the documentation for the 'stat and it says it takes ~20-30V input, so I hoped I was within tolerance.

Once powered on and configured, everything was looking good for the first ~5 minutes. Hot air was blowing out (I had it set to heat). But, then, it looked as if the whole thing went through a power-cycle. The vents closed, then opened again, and it basically stays in this loop: vents open, blowing not much air for a bit, then vents close, then start over again. If I open the breaker and then close it again to reboot everything, I get the warm air again for a minute, but then it enters this loop again.

My question is: where should I begin with troubleshooting? I have verified connectivity of all the wires between the interface and the 'stat, as well as between the transformer and the 'stat & power lines. I have also triple-checked that the right wires are going to the right places. My first thought is that this behavior indicates an issue with going from "stage-1 heating to stage-2 heating", but I am not sure. If anyone could lend me their thoughts, I would really appreciate it!

Thanks a lot,