Turned out to be operator error
but I STILL think there are one too many controls on the darned thing. Don't forget that there is an ON/OFF toggle switch as well as a fan speed switch which has off as one of the speeds.
If you have the fan set on AUTO and the vent won't open, sometimes the gasket gets sticky. Generally you can pull the lever to MANUAL and gently crank back and forth until the gasket loosens up. Lube it with something designed for neophrene. Then with the ON/OFF switch ON and the speed switch on 1, 2, or 3 the fan will operate when the vent is open.
If none of that works, call the Fantastic Fan people and they'll walk you through the process of checking everything out, and send you replacement parts (free) if necessary. Nice people to deal with.