2 are for the driver and passenger temp controls.
1 is for the blend door behind the glove box.
Like Mel's logic and because 2 of mine were noisy, I bought 3 and changed them all at once, not wanting to revisit the issue later.

The problem is that over the years as you dial the temp to the highest or lowest setting, the plastic actuator gears start to round out and just spin, failing to tell the limit switch that the actuator has reached its stopping point. The clicking you hear is the gear/actuator spinning when it has reached the end of the cycle....loud and annoying for about a minute.

So. I changed the one on the drivers side, and like the Video said, its a real PITA.
There is no way to see the screws, I got them out and the new ones in, just by feel.
6mm to big and 5mm too small. 7/32 socket fit pretty good. Also hard to un-plug the wire connector. Pryed up the locking tab with a long flat screwdriver to get it undone.
Put it back in by feel. Maybe just lucky, but the shaft position was pretty close.
No more noise! It was such a PITA that i'm going to let the other 2 sit here till needed. That might be never, hopefully.
:)
P.S. I found another utube video that says there are 4. the 4th one is for fresh air or recirc.