Yes, I'm well aware the A/C dehumidifies the air. What I was referring to is the the A/C evaporator gets wet as it is very cold when the A/C compressor is running and the moisture in the incoming air condenses on it. If one shuts off the A/C without running the fan the evaporator stays wet and can develop an offensive odor. And if one gets back in the car even the next day -- which has been my experience -- upon engine start and the cabin fan begins to blow the inside glass surfaces can develop a fog faster than one can say scat.

By turning off the A/C but letting the cabin vent fan run this dries the evaporator and as the moisture leaves that and then hits the cold air passages and condenses it will dry these out. The downside is in some weather conditions the inside glass surfaces can begin to fog up. More than once I've had to turn on the A/C to clear the fog then turn off the A/C to dry the system.

 

My experience is with the A/C running this defogs the inside glass quicker than just air blowing on it because the air that is being blown out the vents has had its moisture content lowered.

The A/C system has a temperature sensor -- probably uses the outside air temperature sensor -- and if the outside air temperature gets too low the A/C compressor is turned off to avoid the evaporator getting too cold to the point the water that has condensed on it freezes and blocking air flow through the thing.

 

Does anyone know how many drain holes there are ? I think I found 2 of them near the front of the hood, but it's tough to really see much. How would you make sure they are clear ? Running some water thru them and seeing if it drains ?

 

I believe there are 3 under the front trunk lid. One on each side of the battery box and one under or very close to under the battery box.

You have to remove the battery cover -- you can leave the battery alone -- and the cover on each side of the battery. This exposes the 2 outliers and with a good flashlight you should see the 3rd one.

The manual calls for these to be "cleaned" the drains at any rate with compressed air. I never had used compressed air. I remove by hand all the trash then take a pitcher of water and gently pour into the water catch basin and ensure the water drains right out. If it doesn't -- and so far with my cars is always has -- one might be able to take a suitable diameter and length of a rubber hose and gently run it down the drain hole to act as a gentle (there's that word again) drain rooter.

I stress gentleness as you do not want to damage the water catch basins or the drain hose nor do you want to knock the hoses loose from the drain basins.

 

Do you smell antifreeze in the car? If so maybe time to check the heater core for leaks.

 

It can take up to 20-30 minutes, depending on OAT, to raise the evaporator core temperature enough that the condensate begins to evaporate, and now getting it fully exhausted from the cabin, another 20-30 minutes.

Best to leave the A/C OFF, use HEAT!

 

I just drop the top and voila!!!!!!

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Hmmm, while I do understand the theory behind the BS you're spewing, I don't need to "ask myself" anything ...When the windshield starts to fog up, I hit the defog button on the top left side of the climate cluster. When I do this, the defog symbol lights up as well as the little snowflake symbol (that represents the A/C in case you don't know). In addition to these two little symbols the fans also come on full blast. From this point forward it usually takes about 5 - 10 seconds to defog the windshield. If I manually shut the A/C off and leave the fans/heat on, the windsheild stays foggy. That's called annecdotal evidence (in case you didn't know) that the A/C in conjunction with the defog/defrost function, does indeed clear the windsheild. While I've never experienced foam coming from my vents, it's my hypothesis that the foam on my mixer flap is gone (my car has had 2 previous owners), and that's why my windsheild fogs so often/quickly.

 

I got rather tired of my windshield fogging suddenly and spontaneously and added a switch to open the A/C compressor circuit.

Once you make use of the A/C you cannot turn it off(***) absent raising the cabin Rh to the point the windshield fogs over once again, unless you heated the windshield in the interim.

***: You just drove into a cold zone and the A/C was shut down automatically... SURPRISE sudden windshield fogging.. be quick with the HEAT!

Which 996 do you have? My 2001, once the cabin has acclimated to the temperature seating, at least to within 2-3 degrees, does nothing other that route more (coolish) airflow to the windshield.

 

I cover the defroster vents (driver side only) with a paper towel actually, & it prevents my windshield from fogging.
Only happens in the am on way to work, when I get there, I remover said paper towels as it looks rather tacky, lol.

 

Methinks your post be about exterior windshield fogging on a humid day.

My solution is to manually cycle the windshield vent open and then close.

I have no idea why automotive A/C designers have chosen to CHILL the windshield on a hot day.

Or is it fogging the morning following the previous day's use of the A/C... In which case the same procedure will work.

 

I am guessing it is due to humity as you say.
I'll try the recycle trick the next time it happesns, but it probably won't for quite some time now.

 

The idea is that once you start the car you take windshield vent selection out of automatic control by switching it open and then closed. The same procedure can be used to prevent the early morning windshield interior fogging episodes.

 

Is the windshield vent "blowing" when the AC is on, because that's what causes it.

 

Yes, and that's a big part of the problem. My guess is that there was a desire to widely disperse the cooling airflow such that driver/passengers are not discomforted. So, automatically, all three flow routes are open to flow once the cabin acclimates to the temperature setpoint.