I have had this too... hot day high humidity (95+) then late in the evening when the temp drops down to 70's window completely fogs over. Luckily I was in a subdivision so I stopped in the middle of the road and tried to figure it out. Had AC on entire time, tried the recirc but that seemed to make it worse, opened the windows to no avail, turned on the heat but that didn't seem to do much, at least not very after 30 seconds, so I went back to AC and it slowly cleared it up. But as I drove home, through certain areas the window would suddenly fog up and just as face clear up a big down the road. Its all from the temp/humidity combination/difference and I don't think there is any instant fix or cure-all. I have had it happen with ever car I have had in this area.