The problem persists with my Lexus ES350 (with navigation): In humid SW Florida in Summer and late Fall, you start with climate control set on AC with blower speed HIGH or MEDIUM and air discharging from the dashboard vents. Fairly soon fog forms on the outside of the windshield excatly as you describe it and it seems insane to have to run your windshield wipers to clear it. The problem is that by design a portion of the cold air is diverted at all times through the defroster outlets (even thought the defroster is OFF), which cools the windshield so that condensate forms on the exterior surface from the bottom up. To correct the situation, be sure that cold air is recirculated in the cabin, that the blower is set on LOW, and the louvers are flattened to closed position. In LOW blower speed position, cool air through the defroster is minimized and condensation stops, and the cabin is nevertheless dehumidified and comfortable. Do NOT go near the defroster control.
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