I have 2003 gmc 4x4 sle sierra pick up , i am having problems with duel air . Blowing hot air on drivers side when setting on duel air is cold. This the second time in two years.Had shop do it last time and it failed again well i would like to tackle it my self . I have a good idea its the blend door on drivers side just cannot find any diagrams were a how to get to it has anyone had this problem or can pull up instruction on were and how to locate the part. Thanks 