I have had my Porsche 2006 911S for 2 years now. I bought it used with only 6k miles on it. Since I usually only drive it when the weather is fairly nice, I never had to use the front defroster.

Well a few months ago, I drove it in rainy weather, but it was quite hot that day. I had the AC on LO at mid-fan level. My windows began fogging and so I decide to use my front defroster for the first time. Steamy hot air came out even though the AC was set on LO.

Thinking something was wrong, I took the car to the dealer and after leaving it there for a half a day, the mechanic told me it was a normal function of the car. He said the purpose of the front defrost is not to be left on but only for a short period.

Is that normal or was the mechanic pulling my leg?

 

My was the same, and I only had my 06 997 for a few months, and I don't like that feature...!

 

Thats the right behavior.. well the hot air coming out of the front windshield vents, at least. That removes the moisture form the inside of the windshield the quickest - dry warm air absorbs the most moisture.... so the AC dehumidifies the air, and the heater heats it.. once the moisture is gone, turn off the front defroster blower and the AC alone and in-car air circulation will keep the window clear.

That said, if you are getting moist air coming out of your ac/windshield vents for any length of time beyond a few seconds after starting up the AC, then there is a problem with your ventilation and/or A/C system that needs to be addressed. On humid days you typically get some very moist air when you first fire up the ventilation, and with the A/C such cold air can be damp and condense on the window, but once the A/C is up to speed after 10-20 seconds, it should be sending out dehumidified air that absorbs the moisture on the window, not deposit more.

So either your A/C condensor is sitting in liquid (no-draining or clogged AC system ) or the heater core may be leaking (another source of liquid moisture sitting in the ventilation system pathway that gets blown out over long periods of time with the ventilation running). Both are other failures and not a problem of the defroster.

 

It's normal as your dealer indicated. Had the same issue in my Boxster and now with the 997. At start up of the glass fogs nearly completely and, almost immediately, the condensation on the inside glass clears. Switch back to AC and you're good to go. The effect is so pronounced due to the fact that the windshield is small compared to other cars and the system is very effective. As I recall the Touareg did the same thing on occassion.

 

Under the "is this normal" heading, I've had to use my front defroster quite a bit lately with the cold mornings and rain coming to the Bay Area. When I push the button, mine seems to go to full hot, full fan, air conditioner on. It does a great job, but as soon as I turn if off the windows fog right back up again. So, fine, I keep the defroster on turn the fan down manually, and turn the temp down. Everything seems to work except for turning the temperature down. No matter what I do, the air comes out full hot. Is that normal? I get why everything else works the way it does, but shouldn't I be able to turn down the heat?

 

mine does it as well. I did change out the cabin air filter and it seems to have reduced the amount of fogging up on that initial blast.

 

Just picked my car up from the dealer for the exact same issue and was told the exact same thing, that it's normal. It works to get rid of the foggy windows well, but the air gets really hot when I switch it on. When I switch back to auto it's fine. Never used it in our Boxster because we don't drive it unless we can let the top down, which isn't very often in Chicago.

 

It doesn't work well for me, but that is the normal function with our cars (although not with ANY other car I've owned...) The front defrost function will blow hot air regardless of what you set your temp to. I've always had more success defrosting windows with COLD air and the AC on... You can still do this in the 911, but it's manual. Turn on the AC, and then switch the directional arrow all the way up, and that should do the trick...

 

+1 - thanks for confirming that this is normal. Seems kind of lame that you can't control the temperature, but I hadn't thought about the workaround and that's WAY helpful.

BTW, with respect to the family wagon, that CTS-V wagon looks pretty appealing...