window fogging in humid air

It's hot and humid lately and with the A/C running I get a damp mist on the outside of the windshield running about 5 inches up from the base. The wiper clears it away but I get this on no other car. Is this normal?

It's not abnormal - my old 928 could create ice on the windshield in hot humid conditions.

Yes, that is normal. If you want to avoid the lower windshield fogging issue, take the A/C off the "auto" setting and direct more of the air through the dashboard vents. This will minimize the amount of air exiting the windshield vents and eliminate most or all of the fogging on humid days. You can do this by hitting the middle button on the right side of the A/C control panel. The graphic on this button looks like the "dual vents" on the center console.

That will happen on any surface depending on the dew point when running air conditioning. You'll notice it on your house windows at times if you run your cooling down to too low of a temperature.

Tim, Your information is appreciated. Gillie

I complained about it and was told it was normal. It seems like an error to have cold air coming out the defroster vents as that just sets this situation up. I guess it isn't too humid in Germany.

Normal...the stupid "Auto" setting sends too much cool air to the window vents. As stated above, use the vent selection buttons for the dash and/or floor and the problem will be solved. Once the moisture appears it taks a little time to go away after you switch the vents. I have gotten in the habit of not using the Auto button in the summer.

When I returned my 2001 to the factory for shipment to the US I complained of this problem and the rep acknowledged and agreed to look into it. I didn't realize that nothing had been done until about 8PM driving into Birmingham AL after taking delivery at POE. It was July, hot and humid evening and we had just driven through a light rainshower. At first I thought the headlights were failing. But yes, this is a definite design flaw of which the factory is fully aware and refuses to address. Funny thing is that VW has addressed it on their version of the Cayenne(firmware update) but Porsche still refuses to acknowledge that it's a problem, a design flaw, a potentially HAZARDOUS one at that. Some details... Apparently no airflow is routed to the windshield until the cabin is cooled too, or very near your temperature setpoint. Once that happens the apparent level of cooling to the cabin changes dramatically. Part of my complaint in Germany to the factory rep was that in order to be comfortable I had to keep "fiddling" with the setpoint. The windshield is not a very good insulator, obviously, and so the cooling effect of the airflow striking it is lost, mostly, to cool the great outdoors. It is not humanly possible to judge the level of humidity at any given time, especially isolated as we are inside the cabin. So it's a very good idea, most especially at night, to be super diligent about preventing exterior fogging on the windshield by selecting only dash and/or footwell cooling airflow.

It is funny how things come up...i remember this topic last summer i believe...

I have been messing with this on my new to me 02. On mine changing the vents does not stop the foging driving around at slow speeds.. But getting on the freeway does. More air flow somewhere I guess?

It bothers me just as much as my ratteling noise out of my exhaust!

However, the difference being between these two issues is the fogging issue happens during normal operation and is a resut of an inherit design flaw with the way the "Auto" feature directs cool air and at this time there is no "fix" other than not using "Auto" and redirecting the air manually....however, a rattling noise from the exhaust does not occure druing normal operation and is a result of something being "broken" and could be corrected.

Reply to Steve Cole: More than likely "At speed" on the highway more cabin airflow is being "wicked" out the passenger cabin via the two exhauster ports at the rear. Moving slowly the blower exhaust/output (windshield defrost/defog/demist) velocity designates flow direction directly to the windshield. Then at highway speeds with a higher exhauster flow rate the outflow path deviates toward the rear. Just a guess. But it sounds just a bit like you might be talking about interior windshield fogging....???

Yes, mine is on the inside. Is everyone else's not?

I am talking about moisture on the outside. It happens because the cool air sent up the defroster vents chills the windshield. The air on the outside of the windshield cools and reaches the dew point so it cannot hold as much moisture and it drops the moisture on the outside of the winshield fogging it. Mine is also less of a problem when I hit the freeway, but that is because the air flows too quickly to cool to the dew point. Moisture on the inside suggests perhaps a leaky heater, but that doesn't seem like it would be in use in the summer and you would smell the coolant.

Outside condensation here, not inside.

Well, maybe mine is on the outside, now that I think about it? The car is at the body shop getting a GT3 kit installed so will have to wait to check.