How to I test heater/AC actuator?
 

What should the actuator do when I go to test it? I have mine detached from the top of the heater box on my 97 Ranger, but I have it plugged in to the electrical harness. Should the D shaped stem be moving when I turn the temperature selector, or should it be moving when I do something else? Should it happen right away? Right now the D shaped stem is not turning at all no matter what I do.

I just looked at mine visually. With it still attached to box and plugged in. On my truck there is a little door thong to the right of it. Just change the selector on the AC controls and watch the door to see if it moved

Isn't the door you're referring to the one controlled by a vacuum diaphram? The blend door is below the actuator inside the heater box.