Tahoe has no rear heat

[Boog]

My '03 Tahoe with rear climate control is only blowing cold air.
I removed the temp door actuator and it was turned full to the cold side. I unplugged it, removed the cover and manually reset it to center then plugged it back up and it immediately turned to full cold again. For now I centered the actuator and left it unplugged so it does blow warm air.
I found a thread on another site on this topic. Some say the module is bad, some say it was the actuator. How do I test the actuator to know that it is really bad? Or the module? I understand either of these will set a dtc but it's only detectable with something more than just the low end scan tool. I have an Innova tool.
This is only and air distribution issue as there is plenty of hot water going to the heater core.