I tried it too, and found it wasn't a good idea. What I wanted to do, was start the genny to cool the coach at check-in, then switch over to shore tie at our site. Doesn't work. The genny has to spool down to cause the switch to shore tie. By then, the A/C has stalled, and it won't start again till it's had a cooling down/pressure bleed down period. That takes away any advantage of doing it.
The opposite (shore tie TO genny) does work. The ONAN 4KY takes several seconds to decide that it's ready to accept the load, then it pops 120VAC to the ATS and the A/C will actually keep running. OK, so what. Now I know all this and along with the rest, don't recommend doing it. It's gotta be murder on the ATS contacts and maybe worse for A/C and the genny itself.
