Actuator or Control Module problem?

[temo]

I have a 2005 Tahoe and last week the AC was stuck in defrost, I did a simple test: remove and swap the actuator for the one on the passenger side (hot-cold air) and it didn't move, so I bought a new one, however, when I plugged in the driver side still didn't work. I plugged again to the passenger side and it worked fine.

After messing around with the actuators and climate control I notice that as soon as I start the engine the actuator will rotate and get stuck, will not respond to the vents control knob.

Is there a way to troubleshoot the climate control unit?

Hope this makes sense.

Thanks.