Windows Fogging
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Pro
Joined: Apr 2013
Posts: 505
Likes: 51
From: MN
I find it interesting that on many other cars you can have the air flow settings so that the windshield is in defrost mode and you are able to get heat to the feet as well, yet on a 996 this doesn't seem to be an option.
Drifting
Joined: Sep 2001
Posts: 2,467
Likes: 16
From: redmond wa
I suspect it started in the late eighties with the design effort to minimize the space taken up by the Heat, A/C plenum, in order to accommodate all the additional electronics/airbags, etc, etc.
I first noticed this in my '92 Lexus, not to surprised to discover it in my '01 C4.
I think it to be criminal that when you ask for windshield demisting with OAT below 35dF (A/C automatically disabled) what you get is a mode change to "fresh" (if needed), singular airflow path to the windshield, 68dF(***) airflow, less than moderate airflow rate.
***: Assuming a cabin temperature setpoint of 72dF and has already acclimated at that level.
In my '92 Lexus I modified the IAT thermistor circuit such that it "signaled" a 45dF cabin temperature whenever I selected defog/defrost.
Select demist: HEAT & MAXIMUM blower speed!
In my '01 C4 the A/C compressor clutch circuit is open except for actual cooling need.
Rennlist Member
Joined: Nov 2013
Posts: 145
Likes: 1
From: Bergen, Norway
Hello
In my part of the world Bergen, Norway. The wettest and most rainy place in Europe. This is something that most people experience here from time to time.
The cause of the problem is that there is a temperature difference from inside to the outside of the cabin. If the inside is warmer, it can hold more humidity in the air inside the cabin, basic thermodynamics. When warmer air carrying humidity meets a cold surface condensation appears on the cold surface because the temperature of the air carrying the humidity drops, resulting in it discarding some of it's humidity. To minimize this effect one have two options, one: keep the temperature of the inside of the cabin the same as the outside. Or two: always keep the inside of the car dry. I opt for number two of course as it's normally quite cold here.
Recommend buying 997 rubber floor mats (not available for 996), they do wonders, and you see how much water your actually bring into the car with your shoes in the form of a puddle on the mats (in my case). It's difficult to believe but when the floor mats hider the water soaking into the carpets you see just how much water you drag into the cabin.
In my part of the world Bergen, Norway. The wettest and most rainy place in Europe. This is something that most people experience here from time to time.
The cause of the problem is that there is a temperature difference from inside to the outside of the cabin. If the inside is warmer, it can hold more humidity in the air inside the cabin, basic thermodynamics. When warmer air carrying humidity meets a cold surface condensation appears on the cold surface because the temperature of the air carrying the humidity drops, resulting in it discarding some of it's humidity. To minimize this effect one have two options, one: keep the temperature of the inside of the cabin the same as the outside. Or two: always keep the inside of the car dry. I opt for number two of course as it's normally quite cold here.
Recommend buying 997 rubber floor mats (not available for 996), they do wonders, and you see how much water your actually bring into the car with your shoes in the form of a puddle on the mats (in my case). It's difficult to believe but when the floor mats hider the water soaking into the carpets you see just how much water you drag into the cabin.
Last edited by Arne Klinge; Dec 22, 2015 at 09:17 AM.
Drifting
Joined: Sep 2001
Posts: 2,467
Likes: 16
From: redmond wa
Hello
In my part of the world Bergen, Norway. The wettest and most rainy place in Europe. This is something that most people experience here from time to time.
The cause of the problem is that there is a temperature difference from inside to the outside of the cabin. If the inside is warmer, it can hold more humidity in the air inside the cabin, basic thermodynamics. When warmer air carrying humidity meets a cold surface condensation appears on the cold surface because the temperature of the air carrying the humidity drops, resulting in it discarding some of it's humidity. To minimize this effect one have two options, one: keep the temperature of the inside of the cabin the same as the outside. Or two: always keep the inside of the car dry. I opt for number two of course as it's normally quite cold here.
Recommend buying 997 rubber floor mats (not available for 996), they do wonders, and you see how much water your actually bring into the car with your shoes in the form of a puddle on the mats (in my case). It's difficult to believe but when the floor mats hider the water soaking into the carpets you see just how much water you drag into the cabin.
In my part of the world Bergen, Norway. The wettest and most rainy place in Europe. This is something that most people experience here from time to time.
The cause of the problem is that there is a temperature difference from inside to the outside of the cabin. If the inside is warmer, it can hold more humidity in the air inside the cabin, basic thermodynamics. When warmer air carrying humidity meets a cold surface condensation appears on the cold surface because the temperature of the air carrying the humidity drops, resulting in it discarding some of it's humidity. To minimize this effect one have two options, one: keep the temperature of the inside of the cabin the same as the outside. Or two: always keep the inside of the car dry. I opt for number two of course as it's normally quite cold here.
Recommend buying 997 rubber floor mats (not available for 996), they do wonders, and you see how much water your actually bring into the car with your shoes in the form of a puddle on the mats (in my case). It's difficult to believe but when the floor mats hider the water soaking into the carpets you see just how much water you drag into the cabin.
Keeping the cabin (atmosphere) dry....
Remember that a big part of this equation rests on human metabolism, breathing and perspiration.
The solution for that is air flow through, OUT of the cabin, NEVER use recirculate mode in the winter months, and it not a bad idea to manually control/set the blower to a higher speed(/pressure) than that which would be selected automatically... Forced exit airflow, even lowering the windows ever so slightly.