I have one, and it has a switch or rather dial to turn it off and on.
The dial will change the speed from fast to slower.
Now, the thing is broke.
The fan or the switch?
Always try the easiest thing first, so, I've removed the switch and will see if I can find a suitable replacement.
I sure hope its the switch and not the fan.
It's an Emerson unit, not even sure they carry that at the big box unit. Look, right on the side, it's labeled a "FOR USE WITH WHOLE HOUSE FANS MODEL"