I would think it almost has to be in the control panel. When you push the heat or defrost button, it should give power to the fan switch. I would take out the control panel and look for a broken or loose part.
1998 Pace Arrow 35 ft. F53 Ford V10 2012 Honda Civic toad
15 year motorhome service manager. 3 popups....2 travel trailers....5 motorhomes....loved them all.