Odd blend door actuator or HVAC control head?

[2001EAYoung]

My 2001 Tahoe's HVAC is acting weird. I recently checked, replaced and calibrated the temperature blend door actuator because it was grinding (split gear). So after all that was done, I noticed that I now am unable to set the temperature and have the system maintain that temperature. It does this if it is in manual or auto mode, it can't maintain the cabin temperature when the control knob is turned.

 

I can feel the air temperature cycle from warm to cold to warm to cold continuously. I removed the actuator and watched the shaft rotate a few degrees when I turn the temperature knob on the control unit. However the shaft pauses a couple of seconds and then rotates a few degrees, pauses, rotates a few degrees, pauses...You get the idea. It is doing this without me turning the control knob. It continues this cycle until it reaches the end of it's travel and then reverses direction, doing the same cycle of rotating a few degrees, pause, rotate a few degrees, etc., until it reaches the end of it's travel in that direction. At that point it switches direction again and continues this cycling.

 

Sometimes when the A/C is running it stays on full cold unless the control knob is turned to full hot. Anything less than full hot and the actuator begins this back-n-forth cycling of hot, cold, hot. It does this regardless of manual or auto climate control.

 

I also replaced the cabin temperature sensor, above the driver's seat in the headliner. All the temaining controls function correctly: mode actuator switches from floor to vents to defrost, the fresh/recirculating air actuator switches normally, all fan speeds are good. I just can't set the temperature and maintain it.

 

Is the control head bad? Did I get a bad actuator? Is there a climate control code that needs to be cleared?

 

I am baffled.