So it started when I changed the radio and disconnected the battery. I have read that this can somtimes can be resolved by disconnecting the battery again and letting it reset or by taking the HVAC fuse out and letting it reset. I have done both of these to no avail, but when I take the HVAC fuse out the blower then will begin blowing out the vents properly but when the fuse is replaced it goes back to blowing only out the defrost. This is on a 2003 GMC Yukon and it does not have the auto airconditioning, it is the manual dual zone. The rear a/c seems fine. Thanks in advance, Scott