mouldy smell from air vent even without air con operating

[alfatm]

I have opened and replaced the cabin air filter, which was very dirty but dry, but I still get the mouldy smell from the air vent, though a lot more feeble now. The smell comes even with the air con not operational. The car smells nice when I first enter it and the mouldy smell comes from the vent gradually once I drive. Any ideas where in the vent path the mould could be in ? Inside air conditioning unit or just in a section of the path ? Any ideas of further isolating the region ? It is a 2003 alfa 147 .

I also found wet rotting leaves compacted inside next to the foam, on either side of the car's corner where the front hood swivels, just next to the windscreen. So that may not be a cause, the rotting leaves collection, indicates that the car was not cleaned for years in that internal region a possibly cause of how the mould could have been introduced.

thanks
Tony

[Vsix]

if you have cleaned all filters and places , you could try some aircon treatment stuff to remove the smell something like this stuff Forte