On my wife's 99 Durango, it doesn't matter where the selector switch for where vents are it only blows out at windshield. Does anyone have any ideas? Thanks

 

vacuum leak going to the control box, probably the line that goes through the firewall from the engine bay, it is set up to default to the defrosters in case it breaks while you need them, you can drive just fine w/o air coming out the vents, but if you cant keep the windshield clear forget about driving

 

+1

Sounds like a vacuum leak! Check the little kinda harder line that comes out of the same hole from the cab fire wall on the drivers side and see if it is broken. It "T" up right behind the service port with a green label on it next to the brake booster on the left side. Also check all your other hoses.

 

The black vacuum line is the only one that I can't pump vacuum to. Tomorrow I will investigate further. Thanks for all your help. I'll let you know what I find.

 

Meaning the heater core coolant line on the drivers side.

 

Listen closely when you switch between modes (i.e., defrost, floor, etc...). Can you hear a noise for a few seconds? If so, your mode cam may be broken or cracked. This is a small wheel with grooves in it. The linkages for the vent doors connect in these grooves. As the mode cam spins, it causes the linkages to be pulled or pushed in a specific direction which in turn opens and shuts specific pathways for the air flow. If the mode cam is cracked, the linkages can break free of the grooves.

 

Thats what it sounds like. If you shut car off with the vent selector on a position but off you can hear the vacuum leaking.