It should be behind the glove box. Empty your glove box, squeeze the two tabs at the back of the box to release it and allow it to swing all the way out. You should now be looking at your blower motor resistor. It will have at least five wires connected to it and be retained by two screws. It's a very easy do-it-yourself fix. Just disconnect the wiring harness, remove the two screws, remove the resistor module, and replace with a new one. Then reinstall the screws, and reconnect the wiring harness.
Behind the glove box
The resister is right behind the glove box.
Usually if the resistor is bad the heater will only run on full blast.
The front blower resistor on a 98 Dodge Caravan is replaced by removing the cover and disconnecting the wiring harness. The resistor can then be pulled and a new one put in its place.
Perhaps resistor packs on blower motors is defective and need replacement
Failed blower motor, resistor or switch.
It is over the right front strut tower, accessible under the hood.
Blower resistor. I have an 04 that does the same thing. Bad connection between the resistor and the plug for me. Big topic though for durango those resistors.
you might want too check the fire wall on the passanger side right up under the wiper motor it should pull out with a little help.
Often, the blower will operate on only high speed, no matter what the speed control is set to. And a bad resistor, and sometimes the wires near it, will usually be obviously melted or burnt. Remove the resistor and have a look; It's usually just two screws and two wiring harnesses holding it and on later models, it's located behind the glovebox.
under the front passenger seat/ right under the glove compartment
It is on the rear passenger side, all the way in the back. You have to take out the seats and take off the trim panes to get to it. Here is a related "how to" courtesy of Autozone.com. It's how to get access to the rear blower motor, to which the resistor is attached http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c15280041daa