Have had the same problem and have spent the last couple of weekends trying to sort it out. Leaves on the fan grill - removed. Leaves already through the grill and into the internal piping - who knows. Couldn't tell whether the fan housing was wet or dry, however I suspect wet. Pollen filter removed (was dry as was its housing), thoroughly hovered and then washed the pollen filter (would have replaced but due in to shiltech very shortly who will change it anyway, oh and I'm a cheapskate!). Thoroughly dried. Fan on full whilst filter out to try and clear the piping (some more leaves and debris out from the pollen filter housing and also into the cabin.. Drain pipe off (footwell) and drain 'vent' pipe removed and cleaned (no blockage but snipped a bit off the end to be safe). Replaced and re-seated making sure no kinks in either the pipe or 'vent' pipe. Went to the doctor to relocate my dislocated shoulder!
I have a damp cabin and probably a damp fan housing (hence the condensation only on the passenger side), which in this weather will take some time to dry out, so am expecting condensation for some days yet, but now the pollen filter is cleaned and the grill cleared the system breaths better, the screen de-mists more quickly, the fan is noticeably stronger and heat is far quicker into the cabin. No point in cabin recirculation for the moment, as it'll just recycle the damp air.
As a result I noticed.. The under wiper shield doesn't stand up well to repeated removal, well the plastic screw 'beds' don't anyway. The joints between the central shield and the two small side shields are atrocious. Probably about a cm off with the overlap completely visible on both sides. Not at all expensive on Eurospares though, so will replace in the summer. Next the lazy drivers side door window, which was meant to be last weekend's job but got delayed due to the above and two inches of snow, oh and Mrs Tee who gently reminded me I have a wife. (and Mrs Tee's best mate from Uni who was staying with us, and who I had pretty much ignored) Hey ho. gotta prioritise!