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I have a letter right here in hand dated September 11th, 2004 from Rick Podorski, Western Regional Service Manager for PCNA, Porsche Cars North America.

It is in response to my enquiry of September 1, 2004 regarding the status of a firmware update fix for the climate control system in my 2001 Porsche C4. The C4's climate control system often ("part of the system's normal operation." R. Podorski) cools the windshield so severely on a hot and humid day, or night, that the exterior surface of the windshield will fog over, sometimes almost instantaneously.

I had noticed on a web forum that the VW had issued a firmware update for the Touareg SUV that corrected this very problem. So basically my question was if VW has fixed the touareg climate control then the VW fix will probably be applicable to the Cayenne and maybe my C4.

Here is a single sentence from my letter which will indicate just how well we can expect a factory service representative to keep up on these things.

"Porsche Cars can appreciate the time you have spent researching this matter with another manufacturer, but these are two different systems that cannot be compared."

The VW Touareg and the Porsche Cayenne climate control systems CANNOT BE COMPARED!


Maybe someone should inform the workers and/or the buyers in the jopintly owned Porsche/VW factory where both are build using 90% of the same components.

Just as asian manufacturers primarily use NipponDenso, many european manufacturers use Bosch as a resource for electrical and electronic designs. I verified just last evening that an owner of a new BMW has exactly the same complaint. His solution is to lay a towel over the windshield airflow outlet ducts in the summertime to prevent the windshield outside temperature from declining to dewpoint.

Edited by wwest
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The Carrera control unit was made by Hella, the Cayenne and Touareg units are made by BHTC, which is a joint venture between Behr and Hella. BHTC also have a US subsidiary in Plymouth, Michigan. Maybe you want to contact them directly.



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This characteristic is re-creatable on *any* A/C system worth its salt, as the exit temperature of the cooled air should be an arbitary temperature of 5-10C. If this airstream is directed at the front screen, the air will reach its dewpoint on the outside.

Instead of directing the cooled air to the windscreen, would it be sufficient for those users to have it distributed from the face vents an floor vents too? I have the face vents set high so the airstream is not directed to my face, and find this makes for a refreshing interior.

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MY C4 system, and presumably the Touareg and Cayenne, will automatically begin routing CHILLED airflow out of the defrost/demist/defog windshield ducts, once the cabin atmospheric temperature declines nearly, ~75F, to my setpoint, 71F.

I try to always remember to prevent this by manually selecting dash outflow only, or for quick cooldown dash and footwell.

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"worth its salt..."

Give me any, ANY reason, why I would want to CHILL my windshield on a hot day. Keep in mind as you answer that when the Porsche is doing this, automatically CHILLING my windshield, when I actually switch to defrost/defog/demist mode I instantly get HOT airflow to the interior surface of the windshield, just as I should.

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"worth its salt..." 


Give me any, ANY reason, why I would want to CHILL my windshield on a hot day. Keep in mind as you answer that when the Porsche is doing this, automatically CHILLING my windshield, when I actually switch to defrost/defog/demist mode I instantly get HOT airflow to the interior surface of the windshield, just as I should. 


I used my A/C to purposefully chill my windshield today in order to have a rock chip repaired. You did ask for "ANY reason".

Edited by Electric Lizard
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wwest, the penny has dropped and I now see your point. I hadn't realised that the A/C was directing to the windshield in AUTO position. :blink:

FWIW, the A/C in my Audi A4 works faultlessly. (A Hella unit for Audi). When in auto, if interior is cold, warm air is directed at your feet. If hot, cold air is directed to the centre/face vents. The windshield only gets air when you ask it to. (Pressing Defrost or pressing ^ button). This is exactly how I want it to work. It even knows if the engine is not warm enough to heat the air and keeps the fan off until it is.

My Boxster however, just seems to blow the air no matter what the engine temp, which is pretty annoying considering the above. However, if its warm enough to have the A/C cooling - its warm enough to have the top down :lol:

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