A faulty electric door actuator is often the cause of this there is a really good video on youtube showing location and how to replace it.
2005 silverado driver side blend door actuator location.
The blend door is in the hvac box located under the dash on the passenger side.
Blend door actuator locations begin by identifying the problem either defrost mid or floor or temperature modes not working.
I have a 2005 yukon xl and the drivers side air is blowing hot independent of what the climate control is set to while the passenger side is blowing the correct temperature.
Then locate and identify the actuator to be replaced.
These units can be either hanging in front of you or in a little more obscure places such as on the side the hvac plenum.
2005 chevy silverado passenger side door blend actuator replacement.
There were several different actuators though.
There is a replacement mode or blend actuator available at most auto parts stores dorman part 604 107 price 39 99.
The mode door actuator is on the left and the resirc door actuator is at the top of the dash near the windshield.
I noticed last night that one i took out of the truck actually has a couple less pins in the harness connector.
The actuator is just on the right side of the hump in the floor.
I know its the right one since i can manually turn the door with my hand and i get cool air.
Sorry to pop in here just to clarify this is the driver side temperature actuator and the easiest out of 4 actuators.