The defroster doesn't blow any air,the heater and A/C both work fine but there's no air on the windshield or on the floor,just the heater blows air

What is your question?

I'm thinking it's the defroster knob itself-is this possible?

What makes this problem better or worse?

Defroster won't blow air onto the windshield

How long has your 2015 Ford F-150 had this problem?

Months