My air conditioning is sufficiently cold but occasionally I've noticed a little thin film of condensation on the lower surface of the windshield. The area is across most of the width of the windshield in the bottom eighth. This would be on hot days, about 30 Celsius or 86 Fahrenheit.

What is the cause and solution for this problem?


2002 Acura RSX, The air conditioning compressor was replaced one year ago.

  • 1
    Is the distributor in defrost mode? Is air coming to the windshield from the defrost vents right beneath it? In that case try setting distribution to front only and see if it stops happening.
    – Al_
    Jul 20 '18 at 21:21

From your description, this is normal. If you check it out, you'll probably find the condensation is on the outside. You've made the windshield sufficiently cold enough that the moisture is dewing on the outside of it. With how moisture condensates, it doesn't take much on a hot humid day to cause this to happen.

  • 2
    In fact my car did exactly that right after having the system serviced (regas and a new r/d btw, no new compressor), turning AC on and setting the air distribution to defrost mode (it was on a warm day at the end of Summer btw). Nowadays i'm always setting distribution to front (defrost only when Fall is near) and it's no longer happening. Sounds like a healthy AC system.
    – Al_
    Jul 20 '18 at 21:19

The only thing I can think of is if the system is on recirculation mode permanently and humidity is being trapped in the car.

When it is cold and I have condensation inside the car - putting the ac on is the easiest way to clear the moisture...

  • He's stating the moisture is caused when the AC is running. Jul 20 '18 at 20:30
  • Humidity can't be trapped in the car with AC on - it collects on the evaporator and is then expelled from a passage beneath the evaporator. Unless the passage is plugged, of course - in that case he/she would also notice a very wet floorboard though...
    – Al_
    Jul 20 '18 at 21:16

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