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It's a bad blower motor resistor pack. Very common problem on Dakota's and fortunately it's very easy and inexpensive to fix. You need to get a new blower motor resistor from the Dodge dealer. Don't buy one at a parts store, they don't work as well as OEM. The OEM resistor should cost less than 20 bucks. Dodge did a redesign on the resistor pack a few years ago and used much better quality and longer lasting parts. You will see the difference when you compare the old part to the new one. I read online that Dodge sold all their old stock of resistors to Napa.
Look under the passenger's side of the dashboard, down below the glove box in the passenger's foot well, on the bottom side of the HVAC housing. The blower motor itself is to your right, and immediately to the left of the motor is the resistor pack, It is about 2 inches by 3 inches, rectangular shaped and is held in place with two 5/16" screws. It has an electrical connector plug with about 8 wires on it. Disconnect the plug and remove the resistor and reinstall the new one and plug it back in. The fan should work fine after that. It also helps to remove the passenger's footwell vent tube right there in that area, it's not absolutely necessary to remove it but if you do remove it you will have more room to work and easier access to the resistor pack.
Hope that helps.