Hi all....first post...I have a heater problem with my 04 silverado HD duramax...intermittent heat on drivers side usually resolves itself but sometimes doesnt. Heat is always good on the passenger side. It seems to cycle between working and not working. I try to mess with the control on the left side thinking that its the control but am thinking the heater or mixing? door isnt opening. Anybody have some ideas? Thanks

 

may sound weird but unplug the connector from the control unit in the dash, wait a little while and then plug back in. It has worked for me, don't know why. For some reason disconnecting the battery does not have the same result. Goodluck.

 

its a common problem use the search option as its been talked about many times.