I have a 2003 Silveraldo 2500 HD. After a power loss to my AC controller (pulled it from the dash to work on the radio) air will only blow from the defrost. Controller shows correct settings. After starting the engine with the vent selected to front vents, air will blow out of the proper vent for about 10 seconds and then switch to the defrost vents and stay there.
I pulled the HVAC/ECAS fuse for 10 seconds and restarted... The AC didn't correct itself...
I have auto HVAC controls with dual climate zones.