Well, I have to admit that I failed to get to the temp control actuator today. I removed the lower panel with little trouble, but the instructions tell you to remove the driver's side shower duct after loosening the screw at the bottom. That did not work, at all. I removed the screw, but no matter how I yanked, pulled, twisted or pried, it would not disconnect from the main heater housing, which you can barely see behind the dash. If anyone has done it, please share your method!
I disconnected the 12V battery while doing all this, and when I reconnected it everything seemed to work correctly and the code had cleared itself from the HVAC system.
So for now, I'll just see what happens in the coming days.