A little while ago i noticed on my 04 SS that with the heater controls i would put both driver and passenger side to full heat and just the passenger side would blow heat, the driver side would just blow cold air. So i got to thinking well it seems like maybe one of the wires on the plug is loose so yesterday i pulled the dash off and pulled out the HVAC and checked the connections. With the dash off i started the car and turned both sides to heat and it worked fine, so after putting everything back together i try it one more time and it went back to the way it was, no heat for the driver seat. Without the dash the drivers side heat works with the dash it does not.

Any clues on what this could be?

 

A Chevy! (SORRY!) Is there a vacumn hose that is under stress, or maybe cracked? A wire pulled to tight?