99 Expidition
When running the air conditioner a very slight fog can be noticed coming from the vents in the dash. There is also an odor of engine coolant. If you turn off the air conditioner fog and smell go away. Anyone with an idea?

 

Don't use MAX A/C all the time. Sounds like the condenser is being overworked and moisture is being trapped in the duct. When you get close to stopping, turn the A/C to vent or panel and air it out.

 

Your heater core is leaking!
Get it fixed.

 

What he said , heater core is leaking. Or there is a leak where the heater hoses go through the firewall.

 

I vote heater core,had that happen to me.

 

I had thought about the heater core also. I checked coolant level and the floor and found nothing. Does'nt seem to be very repeatable. I tried to get it to do it again in the driveway and nothing happened.

 

That happen to my previous car and got worst and worst until it let go. Check the heater core as suggested.

 

Ditto. You should not be smelling coolant at all. Get it checked pronto