Original post by: Al Poldaas ,
Before you disconnect the battery, make sure your ECC (Electronic Climate Control, if you have that option) is turned OFF. The ECC computer has a program flaw that causes it to overcycle the blend valve motor when seeking its original setting after you hook up the battery, which usually results in a broken gear inside the blend valve actuator. Then you have no control over A/C or Heat, the blend flap usually defaults to A/C which means no heat ever. Replacement of the blend valve actuator is awkward at best and very expensive at worst (most shops will take apart the entire dash to get access). Or if you are very inventive you can make a hillbilly workaround by disconnecting the actuator arm through the back of the glove box, and rig a manual control from coat hanger wire (not elegant).