Defrost stopped working 90 C1500

[OlSmokie]

All of a sudden, my defrost decided to stop working on my truck. It blows hot from the floor vents and it seems to blow out of the dash AC vents no matter where it is set, but there is nothing coming out of the defrost vents. Is this controlled by vacuum or is it electrical? When I switch from floor to defrost, I can hear a click, but it doesn't seem to do anything.
Any ideas would be greatly appreciated.

 

[someotherguy]

On A/C-equipped trucks it's electric; the actuator is on the HVAC box roughly in the area above the gas pedal. The silver "brain box" of your factory stereo obscures the view of it a little bit, if it's still in there.

Common issue is the factory lube on the sliding linkages gets gummed up. Lay down some newspaper to protect your floor and spray the linkages with WD40, work them (gently) a little to free them up, wipe off the excess. Spray some white lithium in there and work them a little more. They're kind of delicate so be careful.

You must be registered for see images attach

Also, sometimes the push nuts fall off the linkages. Not too common but it happens. On the 95-up trucks for some reason the "axle" at the edge of the flap sometimes breaks off, and that sucks bigtime...



On the heat-only trucks it's cable operated but I haven't worked with those at all other than just looking at one.

Richard

 

[ncdmax03]

Would this cause the selector switch to not work at all and be stuck on one setting. And don't matter where the switch is set to