Defrost problems
 

I have a 2008 Impala that recently the windshield defrost stopped blowing. The blower is still working fine, but only blows heat out through the front vents and the lower vents. When I move the mode selector to the defrost setting, I can hear the acuator motor moving, but doesn't move enough to allow heat out the defrost vents. I did read somewhere that when the battery is removed/replaced that the electronic motors go through a relearn process and that if that process is interrupted then they won't work properly. I did recently replace the battery, so I am not sure if this is the problem or if it could be something else. Any suggestions?

More than likely the actuator is bad or the door is stuck.

What's the best way to get to the door so I can see if it is stuck? Remove entire dash, remove part of dash, or from underneath?

Not familiar with the Impala. If you can remove the actuator easily, you try and turn the piece that goes into the actuator and see how easy it moves.

I don't know what years are included on this problem but their was a problem with the door getting stuck because the doors are made from plastic and over time they would warp out and stick. I believe the best way to get at the heater is from under the dash. however it is subject to change from year to year.

There are youtube videos for this.