Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
Which vents blow hot? Is your truck a new body style 2007, or Classic body style?
The problem is in the drivers side temperature actuator. Once the actuator wears and goes beyond the normal travel limits, the control module goes to a default mode (full heat). You can either replace the drivers side temperature actuator or you can have the dealer reprogram the control module (usually around $100 charge to do this).