Here is a common example of what happens. We will pull the unfogged window van out of the garage, drive around for about 10 minutes or so it seems to vary and then it will decide that it is just going to start fogging up. Usually the two front side windows fog up first then the back side and back windows. I've tried blasting heat, turning the A/C on the defrost on (hot or cold, make no difference) rain-x antifog wipes, When it starts fogging up there's NO smell at all associated with it and i run it on FRESH AIR mode, not set in the recirculating air mode . The only thing that seems to start helping is if we open the windows, which is a pain since it is cold outside.