The dash AC on my 95 U280 has been acting like4 there is a restriction in the duct work or fan is not operating at full speed. I started taking things apart looking for a vacuum door or something similar that might not be opening. As a last resort I took the fan out and tested it, works fine. While reaching around in the deep dark recesses of the dash air system I found the piece of rubber below. D.... if I could figure out what it was or where it came from but it was across the fan intake and apparently when the fan came on it was sucked into the opening and restricted the flow of air. I did finally decide that this piece of foam rubber is the lining of the upper part of the plenum, it was glued in at some point and when glue failed it dropped off. I could not get it to stick again so I said the h... with it and left it out. Nice waste of a beautiful fall like Day. :-(
Gary B
Probably there to absorb sound or insulation to keep the outside of the box from sweating or maybe both. Just a guess though.
A little 3M Super 77 Multipurpose Spray Adhesive: strong-bonding, fast-drying glue that (http://solutions.3m.com/wps/portal/3M/en_US/3M-Super-77/Super77/) you spray on the two parts will put it back in place for some time to come ... Should you want to miss another fall day that is :P