Hi, new guy on the block. Just bought my 2003 Silverado. The heater only works when I set heater to manual and 90 degrees. I can control heat pretty good by cycling the fan speeds but if you set tem to say 70 degrees heat doesn't work. Has anyone else had this problem. I looked at the diagrams and found indoor and outdoor sensors but it doesn't show where they are located. If you put it in auto , the heat wont work even is set at 90. Any help will be appreciated.

 

I saw on a post that this guy had the same problem with his 2003 and no one knew what caused the heater problem. He said almost exactly the same as the post above.