Control Head unit issue -not actuators;both behave the same at the same time.

I have a 2001 Tahoe with the manual controls 3 knobs fan, temp, and area setting. Everything seems to work just fine except the recirculate to fresh and back and forth. Sometimes it just seems to ignore the setting from the area knob to recirculate or the button itself. I've swapped the control head unit with a used one once before and it worked for a while. The behavior is typically the same for days, little to no heat in winter or heat vs. AC in summer. Both blend doors have the same output so I know they are both not moving correctly due to a failure to signal or loss of signal from central source such as a relay that the knob and the button share that may have a cold solder joint or loose/poor connection that can be serviced. Does anyone know the electrical diagram of the HVAC control head and solved this issue? I have tried the re-calibration exercise of pulling the fuse for a min, and running the car for 2mins, off and then back on after 10-30 sec.