Foggy windows
 

I am getting mist whenever I run my air conditioner or heater or defroster.
I notice in the summer if I keep the temp at its coldest setting it doesn't do it but turn up the temp control and you see mist coming out of the vents. Now coming into the colder months I am going to need to do something about this as the trucks windows get foggy real fast and I can't do anything about it.
I am thinking I may have a vent that may be partially blocked but before I start looking I thought I would ask if anyone has had this problem.

It has been happening since last winter but I want to get this resolved if I can find the problem.

Thanks for any help.

Leaking heater core, pressure test the rad.

I'm not certain but I have driven maybe 10k miles with this condition without any radiator losses. There is no smell, just a noticeable mist and window fogging.

ON second thought, I will have it tested.
Thanks

Check the drain
 

See if maybe the drain hole is plugged from the heater/ac box. Maybe it's holding some water in there. That could explain the fogging up, but yet no coolant loss or smell.

Check the seal along the firewall, where the hood slams down. I've seen cases before where that is missing or damaged. Your air intake is at the grills in front of the windshield. The seal lets alot of moist air out from under the hood, and it goes right into that air intake.

If it gets real cold outside, make sure you have the vents open to allow outside air in. On defrost the truck will cycle the ac and if there is no outside fresh air in the mix, the windows WILL fog.

If I'm not mistaken on a 2000 the only vent position that doesn't draw in outside air is Max A/C.