Cold Air under passenger side dash
I have a 1998 F250 Powerstroke that I bought just recently. I live in Michigan where it is quite cold. When I run the heater which seems to work ok in all stages, there is alot of cold air under the dash on the passenger side. I have look under and see a vacuum switch which seems to open a door when the heater is on and it feels like alot of cold air is being sucked into this area which causes a cold draft on the floor. Any thoughts on this? Is there a door or shield that may be missing to prevent this cold air? Any help would be appreciated.