06_aspen_sti

I have a 95 RX-7 and my directional air venting system does not work. the venting setting is stuck on full defrost. know matter where you turn the knobe the vent stays on defrost. everything else seems to work, fan speed, A/C, heat. any suggestion. could something have come disconnected from the back of the control knobe or a blown fuse or relay. any ideas would greatly help before i rip apart the dash. lol.