Jeremy Hazeltine

So with a/c on, set to dash, its still,blowing out the defrost as well, which causes the windshield to fog. What would cause this? I know of other cars, the controld are vacuum controlled. Same here?

dporto

The diverter plate in the dash is supposed to be covered with a thin foam. Over time/temp/humidity the foam breaks down and blows out of the vents (perhaps you've noticed this). In anycase, once the foam is gone, the plate has big holes in it so the air diversion is greatly compromised (allowing moist and dry air to blend together)... This is most likely what you're experiencing. If you can get in there and cover up the holes with some aluminum tape or something similar you'll probably be ok...

Jeremy Hazeltine

I have noticed bits of disintegrated foam blowing out on occasion. Where is it accessed from to patch up the holes?

wwest

Assuming HOT and high humidity day wherein condensate forms on the exterior windshield surface.

DANGEROUS in the evening, late evening, when it might be mistaken for fog... Only had it happen a few times, Florida and Alabama.

Once the cabin climate as monitored by the IAT approaches the temperature the 996 climate control system switches to all outflow ducts open.

According to the factory this is done to avoid the discomfort of having MASSIVE cool airflow to your face and upper body from only the dash ducts. method of dispersing the airflow throughout the system.

Best procedure to prevent "CHILLING" of the windsheild is to select and then deselect the windshield defrost/defog/demist airflow mode.

The method I have arrived at is to set the system to max cooling and recirculate, then use the blower speed manually to control cabin comfort level. Slightly increases MPG and removes condenser heat load to the radiators.

Jeremy Hazeltine

this is exactly what is happening, and i am in florida.
i do not use the automatic temp control, i set it to a temp, and do the manual fan control. i have tried switching on and off the, upper, middle, and lower controls, but it seems to end with the same condensed windshield. is there a fix? or is it really "broken"? either way, i wish i could stop it from happening

wwest

If turning the defrost/defog/demist outlet "on" and then "OFF" doesn't block system airflow to the windshield you likely have some sort of failure.

The immediate answer is lay something, towel, magazines, etc, over the outlets.

NOTE: If the OAT and RH are both extremely high the COOL cabin atmosphere might result in this effect.