When I switch from floor heat to off position (fan on high), debris (leaves) fall onto the passenger floor from behind the glove compartment.

Leaves are ingressing from around the wiper shafts near the windshield.

Air flow is also diminished due to restriction.

When warmer weather returns I plan on cleaning the debris.

Disconnect battery, remove glove box, investigate how to open duct work and remove debris.

Eventually the debris will acdify and eat away at the heater core or evaporator thus causing an expensive repair bill.

Solution for future prevention would be to obtain rubber wiper shaft grommets and install them to keep leaves out.