I have an 05 TJ sport that has what appears to be an odd issue:
My vent selector/vacuum lines work and air blows out of the selected position (So no stuck in defrost problems here!). The fan speed switch works as well, except when defrost and defrost/floor are selected. The vacuum lines can be heard and air trickles out the defroster while moving, but the blower, no matter what speed is selected, stops functioning/cuts off when defrost of any kind is selected.
It's cold and snowing here, so this is bad news for visibility!