I'm guessing: Do these work by having a two pole and four pole
arrangement? Switch in the two pole and get 3600- rpm, switch to four
pole and get 1800- rpm, switch in both for six poles and get 1200- rpm.
The geometry migh be somewhat screwed up in 4- and 6- pole
configuration but those are working at pretty low power.

I ask because my neighbour has one of these that only works on high
speed. I suspect the switch but before we commit surgery on it, I'd
like to understand how the thing is suposed to work. TIA

Ted