For my first post, I'll jump in on this old thread just in case it helps anyone else looking for some more info on this. I just resolved the same issue - vent selection not working - in my 94 fzj80, and like the idiot I am, didn't take any pictures, but I might have some useful info.
Like tayzoid1 says, the motor/servo that moves the baffles in the vent system to divert air to different vents is accessible without dismantling the whole dash. All you need to do is take off the bottom piece of trim right below the steering wheel, and then, to really get at it, remove the piece of ducting that connects to the driver side vent. There's just one screw on the top left, then it can pop out.
You'll see a black servo box on the upper right of the drivers footwell. It's about 4" x 2" x 1/2" - it's a decent size, hard to miss. There's 3 screws holding it on, and they're pretty easy to get to with a short phillips screwdriver. Leave it plugged to run a quick test.
With the servo hanging there, turn the ignition to "on" (don't bother starting it) so the AC fans and stuff work. Try the vent selection buttons and see if the servo moves. If it does, then it's likely the actuator arms are jammed so check them to see that they move freely. If they do, then you might just be getting lucky with the servo after having removed it. Here's why:
I wasn't convinced my servo was dead. It just didn't seem like a part that would get the motor fried or anything. So I decided to take it apart. WORD OF CAUTION: keep track of the position the arm is in on the servo, as you'll want to put it back together in as close to exactly the same position as possible. Now take off the nut holding on the arm, and take out the 5 or 6 screws that are holding the box together. Inside you'll see a circuit board, a large gear and a small gear in the corner. SECOND WORD OF CAUTION: note the position of the big gear - same reason.
The magic is under the big gear. Pull it out. You'll see that there two sets of pins connected to the underside of the big gear that slide over contacts on the pcb to indicate what position the actuator arm is in. There was a bunch of grease that had gotten spread all over the contacts and pins - presumably from a lifetime of bumping around and little bits of lube trickling down from the large gear's shaft. I figured this could be the source of the issues if the grease was interfering with the contact between the pins and pcb. So I cleaned off the contacts and pins with a few q-tips and re-assembled the whole thing.
When reassembling, make sure the large gear and the actuator arm are in as close to exactly the same position they started from before you dismantled it. If not, the movement of the actuator arm will not align with the proper range of motion the parts that move the baffles can handle.
I plugged it back in, set the fan to high and selected a different vent scheme on the AC unit. And whaddya know - the servo works!
Now for re-mounting it, it's a bit tricky depending on what position the servo was previously stuck in... but you should be able to figure it out. Move the actuating arms to where the servo's arm fits in it's slot and the mounting points line up. Screw in one mount reasonably tight but leave the others for now to do a quick test, while you hold it in place with your hand. You'll want the wiggle room in case something is wrong. Switch between different vent schemes on the AC and make sure the unit doesn't push itself past it's allowed range of motion. If it does, you'll have to mess with the position of the servo's arm (no need to re-open and mess with the big gear's position at this point). The easiest is to set the vent to one of the extremes (all front vents or all defroster vent), and then work on getting the position right from there.
In case you're wondering, I learned all this the hard way
Whole process is pretty quick, and it saves you from having to source a new part!
