2005 GMC Sierra 3500 Q&A
2005 GMC Sierra 3500 Question: AC won't switch from defrost to any other setting.
There is an electric motor that controls a mode door which switches air flow to the different dash vents. Changing the battery should not affect this motor but as we all know, never say never! You can try disconnecting the battery again to see if you can reset the system. Make sure the ignition is off and leave the battery disconnected for at least 5 minutes, remove the HVAC/ECAS fuse in the under hood fuse box also. The a/c control module will attempt to recalibrate the mode and temp door actuators when when your 2005 GMC Sierra is restarted. Wait about one minute after starting for the recalibration to complete. If the system still does not work correctly after the recalibration then a complete diagnoses of the system may be necessary to isolate the cause of your concern. - Oakman
Had the same thing happen, i started truck got under the hood and pulled the hvac fuse for a few second and put back. Everything works good now - Visitor