If the driver's side temperature does not change when temp control buttons are adjusted, the Lucerne's driver's side blend door actuator is the issue. This actuator can be replaced WITHOUT removal of the dash.
To access the actuator, remove the plastic panel below the steering column (remove 2 screws and panel snaps out by pulling panel straight up towards steering wheel). Once this first panel is removed, the kick panel above the accelerator and brake pedals must be removed (panel is secured with 2 plastic barbed pins, which can be pulled or pried off). Be careful when removing this kick panel, as there is a lighbulb connector that must be unclipped. Also pay attention to how the right side of the panel hooks into the heat ducting, as this this connection must be reattached during reinstall of panel. Once kick panel is pulled off, the small plastic panel on the right side of the accelerator pedal must be removed. Panel is clipped into center console with 2 clips. Pull panel straight off (pull in direction of driver's side door). Now that all panels are removed, slide driver seat all the way back and lay on your back with your head near the brake pedal. You will need a light and a stubby Phillips screwdriver to remove blend door actuator. Actuator is mounted against the airbox (the large black plastic box located directly behind radio). Make sure that you don't confuse the blend door actuator with the recirculation actuator. The blend door actuator has a white plastic lever, whereas the the recirculation actuator has a metal lever.
To remove the blend actuator, there is an air duct in the way. This air duct has a round clip on the top, which secures end of duct to a metal tube. The duct can be disconnected from metal tube by unsnapping clip, which allows duct to be pushed out of the way just enough to reach up and reach actuator mounting screws with a stubby screwdriver. Actuator is held in place with 2x screws. Make note of the orientation of actuator and wire harness BEFORE removing actuator. Remove both screws BEFORE attempting to disconnect electrical connector from actuator. Once screws are removed (this requires patience), the actuator comes right off and the electrical connector can be unhooked.
Connect wire harness to new blend actuator and re-position actuator into its correct mounting position. Warning, do NOT rotate the white actuator lever, as this will damage the actuator. Note that the wire harness must be run on the visible side of the actuator. The actuator has two screw holes for mounting, and 2 holes that align with plastic guide pins on the airbox. At this point, do not try to connect the actuator’s white lever to the corresponding lever on the airbox. These levers are much easier to connect once the first mounting screw is partially installed. Install one mounting screw, but only thread screw in about 2 turns. Once screw is started, pivot the airbox lever until the slot in the airbox lever aligns with the pin in the white plastic actuator lever. (Do NOT rotate the white actuator lever, as this will damage the actuator). Once the levers are connected, push the actuator against the airbox and install the 2nd mounting screw. After 2nd screw is installed, go back and tighten the 1st screw. After screws are installed, the actuator installation is complete. The air duct can be snapped back onto the metal tube.
When reinstalling the kick panel, be careful to ensure that the panel attaches correctly to the air duct. There is a guide lug that slides inside the duct for alignment. Also ensure that rear of kick panel is mounted securely above brake pedal arm, and ensure that panel does not interfere with brake arm motion.
Once panels are reinstalled, the blend door actuator must be recalibrated. This can be accomplished by turning key to ON position, without starting car. Wait 3-5 minutes, during which you may hear actuators clicking as they self-calibrate. After 3 minutes, remove key and then car can be started normally.
