1994 Chevrolet Silverado

Heater problem
1994 Chevy Silverado V8 Two Wheel Drive Automatic 175000 miles

my heater is not blowing hot air. The fuse is good and the fan is blowing as it should as long as I give the housing a little tap. I can deal with that part but I think there is a problem with the damper door actuator or something can you tell me how to go about fixing this?
December 15, 2008.

Is it auto or manual? Is there anything flashing on cotroler?
Temp control motro on HVAC box up and to left of blower. See if it is moving when changing from C to H.
Let me know will be on line most of day.

Dec 15, 2008.