Windshield Fogs at Startup
 

On my 87 300 TDT, the windscreen fogs up when i start the car.

this is more pronounced in the middle of the day, say after the car has been driven, then sat for a period, then started again. the fog is easy to clear, but i am worried that in the very cold weather we get here that it will be more of a problem because it may turn the frost. if i have the whole family in the car the fog is pretty extreme and almost immediate upon startup. it seems to me that there is a lot of moist air being trapped in the climate control unit and as soon as you start the vehicle this moist air is immediately released and fogs the windscreen.

i usually leave the thumb wheel between 22-24 and the selector button on the double-white arrows. i have tried using the EC setting to see if this makes the issue go away but it does not seem to help, if anything it is worse.

i know that a small amount of fogging could be seen as normal, especially with a lot of people in the car, but i don't think this is how the ACC system is suposed to work, fogging the windows immediately at startup.

any thoughts on what might be going on?

You might try using the white down arrow. The owner's manual says that the double white arrow and the defrost setting should only be used when needed - not all the time. The white down arrow is the one that should be used along with the "auto" setting. My windshield still fogs up sometimes like yours. I am not sure why.

windshield fogging is a sign of heater core leak. moisture in the heater box rises to the windshield and on engine start up the heater is in defrost mode until vacuum is built up for heater controls to operate, thus fogging the windshield.
just my $ .02 worth
Joe

The white-down setting keeps the AC compressor running all the time. So the system should be always drying the cabin air. Make sure the drain tubes leading out of the car are clear, and if you smell anitfreeze in the vents, there might be a small coolant leak.

A common cause of windshield fogging can be a tired vent actuator allowing some cool air to flow through the defrost vents, causing fogging. Should not be a problem come cooler weather

thanks for all the replies, folks. i know troubleshooting the ACC can be difficult in a forum setting - and i do appreciate the input from those with a lot more experience that myself. i have the factory manual sections printed out and i have been studying them, which is helpful, but the system is so much more complex that what i am used to.

this sounds very possible. there is a funny smell on startup. it doesn't smell like coolant however, more musty.

where are the drain tubes located?

this is plausible also. i do know for sure that the center nozzle flap actuator pod is bad, and to compensate, the PO had the center flap propped open. but you are referring to a different pod, correct?

I would start at the switchover valve then move to the defroster nozzle.

Is your "funny smell" the sickly sweet aroma of coolant? No mistaking the smell.