Okay....

The 996 has had this problem since 99. Porsche has been made very well aware of the problem and its potential hazards. I have a letter hanging nearby wherein they simply refused to even think about a corrective measure.

THe good news is that you can probably take your Cayenne over to VW and maybe talk them into doing their Touareg firmware fix for this exact same problem.

The problem occurs in my 01 C4 only after the cabin has been cooled to very near the setpoint, 72F in my case. Once that happens a significant portion of the COLD airflow is automatically routed out the defrost/defog/demist ducts (only GOD know why??) and soon after the windshield surface temperature will begin to decline toward the outside atmosphere's dewpoint. The higher the humidity the quicker your windshield will begin to fog over.

I first reported that to Porsche in late May as I returned my 01 to the factory to be shipped to the US. On our subsequent drive from the east coast to Seattle we encountered an early evening rainstorm after a HOT day in August near Birmingham AL. Shortly after driving out of the storm I discovered that I needed to use the wipers to keep the condensation cleared from the windshield.

If you check the 996 thread I think I posted this info there years ago now.

I avoid the problem by manually selecting dash outlets only or dash and footwell if I don't have recirc on, which I mostly do during the summer months but NEVER during winter.

I recently checked with the service manager at Barrier here in Bellevue and we verified that the 04 996 series has the same flaw.

 

I have the same problem on my 04 c4s

 

My 2002 C2 cab has same problem.

 

I have the same problem on hot high humidity days like yesterday in NY. It.s manageable though, I've had other cars that do the same thing but only when it VERY humid outside.

 

Went to Hilton Head last summer. Stopped for gas early evening after the long drive. The whole dang windshield misted up as I got back on the highway!! Had to quickly figure out what those little symbols on the AC controls meant in order to redirect air flow. Even then, some air still managed to get to the defroster.

 

Same problem. I never realized it was a factory issue, I just always assumed that it was my fault for keeping the interior at 66 degree in 100 degree weather.

 

The funny thing is that if you actually select defrost/defog/demist mode, you get HOT airflow to the interior surface of the windshield on the hottest day of summer. Just as it should be IMMHO.

 

It hapens in every car I've had (other brands). Turn the AC on, increase the fan speed and it's gone.

 

I have the same problem. Is it fixable?

 

No the AC is what causes the problem. It cools the windshield to such a temperature that the condensation takes place on the outside of the car. Increased fan speed only causes the area effected to get bigger.

I wondered what the hell I was doing wrong because I have have this problem also (funny thing is I don't remember having this problem with a former Boxster). Since the climate I live in is very humid and hot in the summer it happens every time I use the AUTO climate control in the summer. The condensation will start to appear within 5 minutes or so. I have given up using the auto feature with the AC and select the dash vents and adjust the fan manually. Has anyone attempted to get the firmware update from VW? I had a 2004 A4 rental that had this very same problem.

 

Happens here too. I just use the middle vents button for a few minutes and it goes away.

Worse, if I have the top down, and it's really hot out, I'll run the A/C only to get water all over the center console (vent surround on dash). Really stinks how that happens. Did not happen on my '99 that way, but does on the '04.

 

I tried ReJex on the window to see if this would help, it did not

 

I have a solution....when the condensation gets too bad...GIVE IT A SWIPE WITH THE WIPER! Sheesh

 

I have the same problem with my '04 C4S Cab. And no, it did not happen in my SL500 or 745Li, so I don'y believe this is an insurmountable fact of automotive life in humid climates. The other manufacturers probably increase the flow of non-cooled air to the windshield when necessary.

 

Mmmm,
I have another problem. I have this rumbling sound that seems to be coming out from these 2 obround tubes that come out from underneath either side of the rear of the car. It only makes the sound when I start the car.
Does anyone else have that problem?

Guys give me an effing break. It happens to everycar out there!
Can't see how Porsche can be responsible.
That is what the defrost is for.
And yes I had the same problem, when you do turn on the defrost it blows hot air, BUT leave it running!. I found, on my car at least that it only blows the hot air for the first few seconds, if you let it run, the hot air turns to cool air.
You need the hot air to get rid of the condensation.