Air door actuator fault

Passenger air door actuator does not respond to HVAC controller commands. It stays in the hot position.
I have a GM Tech 2 scanner. When I select a cold temp (15C) the passenger air door voltage readings fluctuate (0.61v-4.83v); when I select a hot temperature (32C) it does not fluctuate (stays at 0.61v).

I tried to re-calibrate the actuator doors (several times now). The passenger air door does respond, cycling through its range.

The air door also does respond to the TEch 2 command to hot or to cold, except it does the opposite of the command.

The Tech 2 is showing the solar sensor readings as unchanged at 235 counts, whether covered with a black cloth or when allowing daylight to shine on them (or about 4.63 v, when changing the readout to volts). I tried unplugging the sensors; each time the voltage went to 5.00 v on the Tech 2.

I replaced both solar sensors with new ones. It made no difference.

I have tried two other used HVAC controllers. No difference, except for one of them, the actuator appeared to respond to commands in the lower half of the temperature range. It did this only once. Despite repeated attempts to replicate this, I could not.

Checked voltages from the HVAC control model to the pass air door actuator and then wiring resistance. Both appeared to be within correct parameters.

Vent temp sensors appear to show the correct temperature.

No codes present, except at first when I bought the car. A previous owner had removed the passenger air door actuator altogether (obviously they could not fix the problem so removed the actuator)