Block off the other vents and see if the other vent blows. If it still does not, then start looking to find the pinched duct or disconnected hose.
Mike
2012 Winnebago Impulse Silver 26QP
2005 16.6 Double Eagle
2018 Jeep Wrangler JK
previously Snowbird Campers,
Triple E Motorhome and Fifth Wheel