The dial that controls where the air is being directed isn't working and is stuck on defrost. The dial itself is still in good condition and I still hear clicks like it's moving into place yet nothing happens. What would be the part that I need to buy to fix this?

Thanks

 

You have lost the vacuum to your vent controls.

It starts at the vacuum tree on the driver's side of the firewall marked "A/C". A small, hard plastic line runs across the firewall, then goes in at the passenger side where the evaporator lines are. It then heads to the vent controls to give source vacuum (yellow line).

Most common is...

1) Hard plastic line has cracked and developed a leak.
2) The line has come off behind the controls.