Yep, I have that problem also. While the air is blowing, you will hear a sound and the air moves solely to the defrost. I usually turn it off, then on and jiggle the switch back and forth and can usually get it back going again. I have not attempted to fix it. I would like to hear more from other who might could give us some details on locating that vaccum hose.
1998 TJ Sport, 4.0 I6, 4.88's, super 35, Auburn lockers f/r, 7" RK, 36 Iroks, 15X10 ProComp series 51, K&N, swaybar disconnects, Ramsey 8500lb winch