That seems to be the idea. I even seem to recall some of these AIOs manuals suggesting that you can stack legs disproportionately within a given range if your 120v needs far exceed your split-phase ones.
Potential downsides include paying extra efficiency costs (generally already higher...
That's on me, really. I was only talking about the HVAC, not the vacuum. Thus my hijack note.
I wish I had any insight into your situation. Hedges seems quite knowledgeable though, my bet would be on their idea.
That aside.. aside.. certainly a frustrating situation, and is totally helping my...