Dear Doctor: I own a 2000 GMC Jimmy. I get heat from all of the climate control vents, but not on the floor setting. When I select “floor” the heat comes out of the defroster. All other settings operate fine. Where is the problem? Brian
Dear Brian: The heater box is controlled by small electrical actuator motors. On some models we can use a scan tool and read trouble fault codes and also use the scan tool to operate each blend door. I have seen faulty actuators and/or faulty heater control panels. There’s the possibility that something has fallen into the heater box and jammed that position of the door from operating in a full direction. If you want to do the inspection yourself, check out alldata.com. They will give you step-by-step instructions and troubleshooting.