If you just remove the rubberstrip on the left hand side and lift the trim an inch or so you should be able to see if there's a pollen filter or not. You can allways fit one if you like; AC or not Anyway, they're only supposed to last for a year or summat So if it hasn't been changed, now's the time.
The last time I changed the filter on mine it was two years old, but they can become very clogged, preventing the blower from sucking in outside air.
I have also seen old filters where fungi got stuck in the filter element and when it got wet from AC core condensation water the whole thing swallowed up and looked like something out of an alien movie, not to mention the smell . This won't happen on the 156 though as the filter and AC core is far apart.
Ok thanks, I was asking as I seem to have a problem with condensation so was wondering if it blocked anything when "full". My 156 cannot run with just the normal airflow if its even slightly damp outside...gotta have the aircon on to dry the air and prevent misting