2002 S80 Warm air from floor

[djackson47]

This is really weird. The HVAC system works fine in Auto; all is comfortable and the ac blows nice cold air. However, as soon as a window or the sunroof is opened, warm air flows up from the floorboard. It doesn't matter whether the ac compressor is engaged or not. As long as the passenger compartment is closed (windows up and sunroof closed), all is well. It's really annoying, because I can never drive with a window or sunroof open because the air coming from the floorboard is too warm for comfort. I recently had the transmission rebuilt and thought perhaps they left a vacuum undone, but I can find no evidence of this. I also haven't found another post like this occurrence, so any help would be appreciated.

[BobbyMang]

Did they remove the exhaust heat shields from the bottom of the car? Or at least missing one? Also, where on the floor does it flow from?