The air vents would just click like crazy trying to open.

2006 Ford Expedition began to make a knocking sound when I turned on the rear A/C. Dealer says the gears on the actuator that open the rear A/C vents are made out of plastic and the teeth break off causing a flap to continually slam shut which is what makes the knocking noise. Dealer replaced the actuator for $400. This is what happens when parts are cheaply made. Time to wise up Ford!!!

The air comes only through the upper when you just started the AC, the computer does not let you to make the air come through the front holes, when the temperature inside is not that hot, the computer unlocks this thing, so the air can come through the holes that you choose... this is very uncomfortable during summer