windshield fogging/condensation

Asked by Jul 05, 2009 at 10:23 PM about the 1990 Lexus ES 250 Base

Question type: Maintenance & Repair

while driving with ac on the windshield starts to fog up from the bottom and works its way up.  The condensation is on the outside and I have to run the windshield wipers to clear it.  I suspect that the heat from the engine is hitting the cooler windshield and causing this problem but how can I correct it?

1 Answer

30

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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