Please get an electrician. You don't seem to have a grasp on this at all.......that is not a criticism. I probably can't figure out whatever you do as a profession ( especially if it involves computers!)
I don't agree with any of your proposed assumptions. Also, the motor may or may not be capable of running on a speed control.'
Specifically, your model came with INSTRUCTIONS! That is how to hook it up. If you could scan the wiring diagram and post it, we could offer some suggestions. But for now, I suggest you do nothing until you or we get this figured out.