AC won't switch from defrost to any other setting. on 2005 GMC Sierra 3500

Changed battery. Now ac switch won't change from defrost to face or feet setting. What is the problem and how can I fix this?

by in Swansboro, NC on September 24, 2009
2 answers 3 comments
ANSWER by on September 25, 2009
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.
ANSWER by on July 25, 2010
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
COMMENT by on July 29, 2010
I have a 2004 with the same problem so I unplugged the fuse for 30 seconds, started the truck waited for a minuet and started the AC and it worked fine.
COMMENT by on March 12, 2011
It happened on my 2005 also. I pulled the 10 Amp HVAC fuse under the hood for a few seconds and the system works again. Thanks for the tip!
COMMENT by on June 10, 2011
Took several attempts, but I started the engine, took the HVAC/ECAS fuse out for 10 to 15 seconds and then reinstalled. Everything went back to normal. This may have started from trying to start the engine with an almost dead battery and not the actual battery replacement. I'm not really sure. It may also be a good idea to turn off the HVAC unit and or pulling the fuse before disconnecting the battery for any reason. Thanks for the input folks!

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