With the heat/ac off, there is a light mist that comes from the vents. The windsheild also fogs up w/ defrost on .
A/C not working on 1999 Dodge Durango
Sounds to me like it is time for a heater core...
I wonder if the heater core is leaking? Do you smell hot antifreeze or have you experienced coolant loss? To find out if the heater core behind the dash is leaking the cooling system will need to be pressurized with a pressure testing tool. A leaking heater core will cause the windscreen to fog up.