I'm finding the 2002 is electronically controlled, but then I also see that there is vacuum to the climate control system which would indicate it's still vacuum operated?
Vacuum diagrams and mention of an electronic control here - http://www.2carpros.com/questions/dodge-durango-1998-dodge-durango-vacuum-diagram
If it proves to be electronic I would run the fuses with a circuit tester. Alternately check your manual to see if the electronic control is on an identifiable fuse, though it may be grouped with other dash accessories so you might have to hunt down a wiring diagram, I hate tracing those things.
Seems also that those with vacuum operated servos the vacuum line from the manifold t's with one line going to your cruise control actuator and one through the firewall to the vent actuator, I have seen the diaphragm go bad in cruise controls, that will cause no vacuum to the vent control. - http://www.fixya.com/cars/t2416712-heating_air_conditioning_control_stuck
- if that's the case then plug the line to the cruise control until you can get it fixed, no cruise but a properly working heater is preferable in my book.