Count me in - same issue!
2002 Highlander V6 manual temperature control.
Center AC control (temperature) got "sloppy" and continued to hang on for about two months. Now I have the
HOT AIR conditioning feature that Toyota seems to include in many models. I will try this fix since it sure sounds like it worked for everyone thus far and mine does do the changeover when moving the control knob. As a side note, I did find the part online for "only" $458.00.
Glad I researched this issue and found this site! I will post results.
Jim