1st-pop the covers fron under the steering wheel-looking towards the center you'll see 3 actuators-top is dash, middle is defrost and bottom is floor. start the jeep and move the selector around and see if anything moves. if it does, check the arms to make sure not broken/disconnected. if not, make sure hoses are connected to the actuators-top/bottom have 1, middle has 2(thin and colored-look like wires, not hoses) if connected, remove the glove box and you'll see a connector with a bunch of colored hoses to it-make sure it's tight and connected.
this is as far as i made it as my problem was at the connector(1 hose cut) if it's connected and looks good you'll have to keep going and disconnect, remove center dash and look at the switch. this is about as far as i can help as i didn't need to go past the connector. sure others can guide you farther.