I have been having recent problem of air flow comming from floor outlets only after 2500 Ram cummins has set for a few days. I have good air flow but only on the floor vents. This has done this previously and turning the selector sw. to BI,Floor , Upper positions back and forth would normally get it to change to the upper vents. Appears to be the selector switch. Is this electrical or vacuum switch ??? Stuck linkage ?? Antone had this same problem.

2002 Dodge Ram 2500 Cummings

Thanks