I have a 1998 Dodge Durango with the 5.9L engine. Changing air temperature from cold to hot works fine and air blows to the floor and the defrost vents but not through the front dash vents. This is true no matter which air mode setting is selected and the problem is present at idle or at speed. There are no unusual sounds associated with the failure. This problem came on gradually. Air to the front dash vents worked fine then turned on more and more slowly with less and less air volume until failure. All vacuum lines under the hood and dash seem good as I could find nothing disconnected or broken.I think it may be a bad actuator or stuck mode door problem. I don’t know how to locate either one and can’t find a hvac diagram online. If someone can help me find them and troubleshoot it would be appreciated.

 

The default position for the hvac system with no vacuum is defrost.