[A4] Fogging Windows...

Stephen Kormilo stephen at kormilo.ca
Tue Jan 15 16:57:49 PST 2008

I generally run with Econ ON, i.e. no A/C, but in cool, rainy weather
experience the fogging window symptom. Pressing the front defrost
button, which turns the A/C ON, even if Econ is ON, takes care of the
fogging pronto. OTOH, the windows will fog up again pretty quickly after
turning front defrost OFF. I'm pretty sure that the residual moisture on
the A/C core causes the rapid re-fogging, so as soon as I get a fogging
problem, I will turn Econ OFF. After that, just running the climate
control in Auto generally keeps the windows fog-free, requiring only
occasional bursts of Front (&/or Rear) Defrost.

Derek, if your window fogging is as severe as it sounds, then there 
might be a problem with the Cabin Air Recirculation control, as noted by 
Nick below. Recirculating the interior cabin air will cause a rapid 
increase in interior humidity, which causes the fogging. I never 
recirculate cabin air, preferring the 'fresh' outside air to be drawn 
into the car. I'm not sure which year your A4 is, but IIRC, in 'all'(?) 
A4s the Audi Climate control has an air pollution sensor that 
automatically causes cabin air to be recirculated when exterior air 
pollution is detected, regardless of the setting of the Cabin Air 
Recirculation control (if present, again IIRC, later B5s & B6s had a 
Climate Control ON/OFF button instead of the Recirculation button). 
Possible source of your fogging problem? I'm not sure if a scan would 
pick up such a fault or not.

Stephen Kormilo
Nanoose Bay, BC

2002 Audi A4 3.0 - Silver
1998.5 Audi A4 2.8 - Silver
1985 Mazda Rx7 GSL-SE - Black

email: stephen at kormilo.ca

Nick Thompson wrote:
> This is just a shot in the dark, but are you running the cabin air
> recirculation in the on or off position?
> I've never had this issue w/ my Audi, but in my Accord, if I run the
> cabin recirculation instead of fresh air, the rear windows (just the
> edges) seem to fog up.  If I run fresh air, it  clears up.  Sounds
> strange, but I thought I would put this out there just incase....
> Nick
> Rocky Mullin <caliban at sharon.net> wrote:
> here's what i would try. we have a home-sized dehumidifier. i'd put
> my car in the garage, pinch a flat cord through one of the doors, and
> run the thing in the car for a couple of days. barring better
> suggestions :)
> On Jan 14, 2008, at 8:33 PM, Derek Pulvino wrote:
>> Wondering if this is a common problem, and if so one that also has
>> a common solution.
>> Only really notice the fogging occur when the weather gets cold
>> (like down to 35-Fahrenheit or so), with any precipitation making
>> it worse. Most accumulation is on the edges of the windshield, tops
>> of the front windows, and pretty much all of the rear windows. I'm
>> not aware of any leaks in the car, and I've got the climate control
>> set to Auto, Econ off. Didn't get any faults with the CC in running
>> a scan.
>> So, any ideas?
>> dp

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