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 2500 HD Heating and AC Temperature and Air Delivery Mode Door Actuators May Fail
Chevrolet Silverado 2500 HD Problem
Average Mileage: 125,800 mi (75,000 mi - 200,000 mi)
Visitor, 2004 Chevrolet Silverado 2500 HD, 75,000 mi
Yes, sometimes you turn the ac on and the heater comes on for a while then it will take 5 min or so and it will finally switch to cool air.
Visitor, 2001 Chevrolet Silverado 2500 HD
some time it wont go into coling it heat,s instead hasent ben fixed
Visitor, 2004 Chevrolet Silverado 2500 HD, 85,000 mi
blowing cold air then after much trying with slide selecters a little heat then nothing.Will take to the shop soon.