Hello my new to me 2004 accord coupe has a problem with the ac buttons. The buttons that redirect the air to like defrost or to feet only do not work. They light up when you change them but it always just blows out through the front vents only. What could be the problem? The previous owner did put in a aftermarket stero could that be the problem? A fuse maybe? Any help is appreciated.

 

There is a thread on how to get HVAC codes in the DIY section. You should give that a shot.