Fogging Windows

Maintenance/Repairs
1

During the winter, or when it is unusually wet, I have a significant fogging problem with my 2000 Acura TL. When the car is completely cold inside and out, as soon as the engine starts, the lower windshield fogs then clears up (sometimes the rear window as well). Then, once the car warms up enough for the heat to start (automatic climate control) the windows begin to fog immediately. I switch on the defroster, but it may take 5 minutes to clear the windshield. Recirculate is not on (at least according to the switch). I have no smell or apparent coolant leakage. The carpet is not wet. I even run the A/C 100% of the time to try to help, but it doesn’t. Any ideas?

2 
You may have a leaking heater core or maybe more likely a clogged condensation drain.   Have you checked to determine if any of the floor mats are wet?
3

Sounds like you have an air leak to the defrost vents. It sounds like some of the air meant for the floor vents is coming out of the defrost vents because the air damper isn’t sealing tightly. The small amount of warm air hits the cold windshield and it fogs up.

4

I checked the the dampers which appear to be working fine. I also replaced the related motor. That seems to have helped some. There is another symptom. There are times when I will arrive at my car to find that the windows are partially fogged. Today, for instance, I came out to my car after work to find the back glass fogged up and the lower driver’s side of the windshield fogged up. The car had been sitting for about 6 hours, temp was about 35F, and no precipitation. Also, the car was parked on a slant with the driver’s side on the downhill side of the slope.

I smell no coolant, no musty smells, and I can find no dampness on the carpet, etc.

5

I used to live in the Northeast, and I can recall leaving all the windows open on clear days, especially in the Winter, to dry out the interior. Also, take out the floor mats and bring them into your warm house overnight to dry. Sometimes, if the car was in a safe place, I’d leave all the doors and sunroof open all day. Just remember to turn off the interior light. All that might not help, but it can’t hurt. Keep your insurance paid up so if someone steals the car, you are covered. Maybe that would be OK anyway.

6 
 [i] I smell no coolant, no musty smells, and I can find no dampness on the carpet, etc. [/i]

But it is there, or else the windows could not fog. It does not take a lot to start fogging windows. It may be nothing more than the moisture from your breathing and body or moisture brought in by wet or snowy shoes.

If you can't find a source, make sure you keep the re-circulate button OFF to allow fresh air and keep the ventilation fan on when ever you are driving, even if the car is not warm yet. I would even turn on the AC, even if it was not hot, to help dry things out. 

I would also keep an eye out for clogged drains (that includes sunroof drains).