The Tech-2 eliminates any guess work into what is going wrong. There are two temperature actuators, one for the driver and passenger. The driver's side actuator is under the passenger footwell, just to the right of the center console and left of the cabin filters. The passenger side is directly above, more or less, accessed through the glove box usually. The guts are the same but we have different generations so consider that. You correctly identified the other two, Mode and Recirculate.
Even after researching these actuators for three years, I still came across conflicting information. Several GM dealership websites and ACDelco all gave conflicting information. The first actuator purchased was the wrong one of course. Ordered the other and all was well. When the wrong one was in, AC was blowing hot, counts were backwards almost like we put it in backwards which is physically impossible.
On the GMT900s, if you replace the main control unit, it has to be programmed. Not plug and play.
