2001 Tahoe Odd Blend Door Actuator/HVAC Behavior

[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 the system is in manual or ACC (auto mode). The system 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 in the same direction, pauses, rotates a few degrees in the same direction, pauses, rotates...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 endless cycling.

 

Sometimes when the A/C is running, the temperature will remain 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 remaining 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 have the system maintain that temperature with the temperature control. The system used to work correctly, either in manual or ACC (auto climate control), blending cold and warm air as the temperature control was rotated to the desired setting.

 

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

[Doug_Scott]

My experience with the newer(for me anyways) is very low, but, one thing I have heard repeated a lot is that auto temp control systems that are acting in a strange way can sometimes be corrected by simply disconnecting the battery for 30 seconds or more, then reconnecting will cause the system to reset itself.  Have you tried that?