I have a 89 chevy xcab 4.3 eng. My heater works fine but the problem is
when i it the switch to make it go to defrost no air blows out. It blows
out the middle and bottom fine.When i hit the changer switch i can hear it
click to the diff positions. Do i need to replace the heater control
assembly. Or is there some sort of motor that directs the air flow.Any
help thank you