What is the make/model of the AC unit? What does this wi-fi port looks like? I recall seeing people doing some wi-fi dongle thing on their Midea or Toshiba or Panasonic units - you might get lucky searching Github.
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Specifically regarding this:
So if power monitoring means would not work for you, maybe… depends on the style of your AC unit, this might also help if your AC has a motorized cover that would flap open when on (common for those non-central AC setups). And then some regular door/window sensor could see whether your AC is on.