A/C problem. Panel or actuator?

The car has dual zone control sliders driver/passenger. The DRIVER'S side does not turn cold or hot, it stays the same unless you keep pressing on the slider.

I popped the dash cover and looked behind the panels to see the actuator. It IS working and it turns when you move the slider, but it turns back to neutral (center) position once you let go of the slider.

It doesn't matter which way you move the slider; up (hottest) or down (coldest) the actuator will turn to the correct position but it returns back to center position.

http://i68.tinypic.com/2hs8429.jpg

Would this be a problem with the Control Panel or the Blend Door Actuator?

I've replaced dozens of actuators on "W" cars- never a control head (you say panel) so I'd play the odds..but I will say they generally fail and quit working altogether due to a cracked gear- take your actuator apart, is gear cracked? there is a seller on Ebay who sell new steel gears.....for 1/4 th the price of a new actuator...

If it stays in place as long as you hold the slider, I'm thinking control head......check the numbers on the actuators for both sides...if the same swap them, and see what happens....

Update.

It wasn't the actuator. I replaced it and the issue remains. So eBay, here I come.