Will not switch to defrost?

OK that car uses the actuator to move the cam (white gear) that gear then moves the levers under it that actually move the doors themselves. The levers are a common failure item. As you can access the cam already you can likely see the mode levers in the first image as well They are under the cam. Replacing them isn't that hard but you have to time them correctly and then install the cam and perform the mode cam learn procedure. The parts all snap into place. The basic process is, remove the actuator, then release the tab in the middle of the cam and pull the cam off. Now look at the levers, are both in place? Commonly they gear or lever cracks and falls off. Get the replacement parts, then to install them you push the gears onto the shafts, then rotate the gears one at a time until the internal door stops, now you put the levers into place with the last tooth engaging the gear, repeat that for the lower lever. Then you snap the cam into place and then rotate it to be sure it is moving both levers. If it is then install the actuator. Now you need to do a recalibration. The scan tool is the easy way but if you don't have one, go to the fuse panel and remove the HVAC Module fuse 54 in the underhood fuse box for 20 seconds. Put the fuse back in, turn the ignition on and the actuators will run the calibration. Test that it all works. I commonly replace all of the plastic gears and levers because they get brittle.