2002 Windstar A/C Temp Control Issue
 

Hello All; I have a 2002 Windstar with the front / back A/C. If I slide the front temp control switch to the left (cold - blue), I hear a very loud clicking noise coming from up under the dash. If I slide it a 1/4" to the right, it stops. If I keep pushing it to the right (hot - red), the noise becomes a very low level "thud" sound which continues until I push it back toward the cold. I'm sure it has something to do with the temp control, but can't find it. Can anyone offer assistance as to how I can find it to either replace it or see if something has become stuck in it? Thank you!