I have a 98' C-class and recently replaced the cabin air filter. The blower motor is under/behind the glove box with the filter to the left of it, toward the center consol.

While replacing the cabin air filter I noticed leaves and debris in the vents, left of the cabin filter. This, and the thought that filtered air should flow through the blower motor, and not dirty outside air, got me to question which way the air actually flows.

Does outside air first pass through the blower motor before being filtered? And why would there be leaves and debris, in the vent left of the filter, with leaves and debris on that side of the filter (the side that faces the cleaned air)?

TIA
MarkC