[hatzie]

If you leave the actuator hanging, without being bolted or latched down and connected to the linkage etc inside the HVAC box, the HVAC controller will still be angry with you because it can't calibrate the stop locations.

Why?

The actuators don't have stops because it's less difficult to assemble and service if you don't have to line up timing marks and the engineers figured someone would mis-assemble them and break parts... out of stupidity, malice, or haste. A for engineering effort. They made em easy to assemble and easy to service... but people can still screw them up. Nothing is foolproof. Fools are too ingenious.

What the procedure I outlined in my last post does is cause the HVAC controller to run a calibration cycle.

Here's what it's doing... The HVAC controller cycles the actuators several times from stop to stop. This calibrates software stops based on the current draw on the tiny little DC motor in each of the actuators. Once the running current is known, between the linkage travel stops, the HVAC controller can accurately determine when the linkages the actuators are attached to have reached the end of their travel by the rise in current above the "normal" current needed to run the linkages.

If the linkages or doors bind up the HVAC controller will think they have reached the travel limit and stop. The small DC motors are completely capable of breaking the linkages and stripping the internal gears in the actuators. The controller limits the torque applied in an attempt to avoid that.

Boy that was wordy. Hopefully it's clear what's happening.

BTW: GM used this same scheme in many vehicles. The last generation of W-Body Impalas are notorious for the HVAC actuators stripping gears as they age and get brittle.