One or more heater & AC (HVAC) air delivery and/or temperature mode door actuator may fail. This can result in incorrect air delivery or temperature. If this occurs, fault code(s) stored in the HVAC control module should be available to assist with diagnoses.Google+
Car Problem Reports
Chevrolet Silverado 3500 Heating and AC Temperature and Air Delivery Mode Door Actuators May Fail
Chevrolet Silverado 3500 Problem
Visitor, 2001 Chevrolet Silverado 3500, 202,000 mi
If u switch from a/c to heat or vis- versa the heat or a/c stay on when you want the other if i shut off motor an cool it for several minutes upon restart the heat- a/c you wanted starts.