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Discussion Starter #1
During wintertime, I normally default to warm air directed to the windows (using the "defrost" vent direction) to keep the windows clear of fog on my other cars. This is usually good enough, and even then I can drive around with warm air directed to my face most of my time and only use the defrost vent direction occasionally. Only in very rare cases do I need l turn up the heat and fan speed, and turn on the AC in order to defog the windows.

On my Boxster, this doesn't work at all. With the vent directed at the windshield, fan at medium, and temp set to 65, all the windows fog up every ten minutes, and I need to turn on the "nuclear option" defrost switch to blast my windows clear. This is complete overkill and gets the cabin way too warm.

What do you guys do?
:helpme:
 

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That's strange, my windshield and windows stay pretty clear. I wonder if your recirculation valve is stuck on?

Make sure the glass is clean inside and out. The heat from the defroster may actually be vaporizing some plasticizer residues that start to condense on the inside of the glass again as soon as you turn it off.
 

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Should only fog up if its detecting exhaust fume and switching to auto-recirculate...or you have max AC enabled. Normally, new air is brought in the same humidity as the outside and there is no fog.
 

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When you say that you direct the air to the windshield, do you mean you aim the slats, or do you mean that you push the button that directs the air to come out of the defroster vent? I believe that if you do the latter you should get defrost action without the nuclear option. If not, something is happening that I don't understand.
 

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Good point, there is an option buried in the menus to enable/disable airflow to the vents on top of the dash. I keep mine enabled. Maybe windshield fogging is more likely if you turn that option off?
 

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Discussion Starter #6
When you say that you direct the air to the windshield, do you mean you aim the slats, or do you mean that you push the button that directs the air to come out of the defroster vent? I believe that if you do the latter you should get defrost action without the nuclear option. If not, something is happening that I don't understand.
I mean, I push the button that directs air to the defroster vent.

Any idea how to check if recirc is stuck in "on?" And where is the menu option for enabling the top vent? (I don't have PCM.)
 

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There is also an option to disable auto recirc. Go into vehicle-settings-air cond in the MFD, IIRC.

BTW, I turn off the top vent option for top-down, and turn it on for top-up.
 
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Discussion Starter #8
It turns out that I *did* have auto-recirc on, which was probably the source of my problem. I turned it off; we'll see if it improves things...

I also had the airflow to the vents on top of the dash turned off in the settings, but according to the info screen, that setting is related to auto-air con somehow. In any case, turning that setting on or off did not alter how it behaved with the dash button pressed to direct air to the defrost vents. Those vents on top of the dash appear to work whenever the "face vents" are working, not when the "defrost vents" are working.

:thanks:
 

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It turns out that I *did* have auto-recirc on, which was probably the source of my problem. I turned it off; we'll see if it improves things...

I also had the airflow to the vents on top of the dash turned off in the settings, but according to the info screen, that setting is related to auto-air con somehow. In any case, turning that setting on or off did not alter how it behaved with the dash button pressed to direct air to the defrost vents. Those vents on top of the dash appear to work whenever the "face vents" are working, not when the "defrost vents" are working.

:thanks:
Good discoveries! Will be interested to see if you get better results. It's possible that even with auto recirc on, it wasn't recirculating because it didn't decide to do it. Could you say more about the extended vent settings related to auto air conditioning? I do think it's probably right that the vents on top of the dash work with the face vents not the defrost.

You're welcome and good luck!

Another possibility just occurred to me: some folks here have reported that their cars were delivered without a full charge of Freon. If your air conditioner is not working properly, it won't be dehumidifying enough for good defrost.
 

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I have had this misting problem from time to time, but only because I push the "AC Off" button most of the time (except when humid or raining).

Does anyone know whether or not the AC compressor is temporarily turned off under WOT?
 

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The A/C compressor is normally never turned off in these cars, unlike the way they have worked in the past. Rather than a mechanical or electromagnetic clutch the compressor uses some kind of linear mechanism called a "swash plate," according to the service information book. If the "AC Off" button forces the compressor all the way off, then it's not clear what's really going on. I've never felt the need to hit that button with the automatic climate control system equipped in my car.
 

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Discussion Starter #12
It works much better with auto-recirc deactivated in the software, even with the AC button set to “off.” Now it works like a normal car... Thanks for the tip! I never would have guessed that a SW setting was overriding the HW button... Keep It Simple, Stupid (Porsche)!

Regarding the upper vent menu item and auto aircon, here is a screenshot of the rather hilarious info screen describing the function:

Top Vent Description.JPG
I have no idea what it could mean and why the message is so badly garbled; is not difficult to find German people who can speak competent English.
:taunt:
 

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The A/C compressor is normally never turned off in these cars, unlike the way they have worked in the past. Rather than a mechanical or electromagnetic clutch the compressor uses some kind of linear mechanism called a "swash plate," according to the service information book. If the "AC Off" button forces the compressor all the way off, then it's not clear what's really going on. I've never felt the need to hit that button with the automatic climate control system equipped in my car.
Interesting information; thanks. The reason I asked about compressor decoupling during wide open throttle is because my 997 GTS noticeably decouples the compressor when I floor it with the AC running, but I haven't noticed a similar effect with my CGTS. I guess the mechanicals differ between the 987/997 series and the 981/991 series.
 
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