Defrost/vent adjustments

[Zilverado]

So I'm starting to have trouble with the truck not blowing hard out of the defrost vents at the base of the windshield - mostly blows from the a/c vents.

This was a fairly major concern the other day when I drove it back from the country in the dark in a pounding rain. The high humidity fogged to windshield up something fierce. Finally after playing with the controls a bit, the air volume seemed to increase.

So I've had the air box off before to replace the heater core, and I think I remember there being vaccuum and cable controls. I think I just need to adjust the damper, but is this a tricky job? Or would my vaccuum actuator be weak?

Any thoughts?

[PHOENIX]

I know the a/c models have vacuum lines and what not so I dont know if this helps you at all.

I dont know about a/c trucks. But heater only truck have two cables.
1. Controls the heat temperature (cold, hot - controls door at heater core)
2. Controls the heater / defrost door.
- When the switch is turned "off" the "heater" vent is the only one open.
- When its set to "heater" the "heater" & "defrost" vents are open.
- When its set to "defrost" the "defrost" vent is the only one open.

Maybe your cable is not hooked up properly or not at all. Check the cable that is under the dash (under the ash tray). Take the little washer off the pin and pull the cable off and try to activate it by hand and see if it moves freely. Also turn the heater on and test it while moving this lever by hand. Then turn the defrost on and test it moving the lever by hand. Maybe youll find whats wrong.
Again none of this may apply to a/c models, I dont know, just trying to help.

Looing in a book it looks like there is a vacuum defrost valve for the a/c trucks.
I would think its still right there around the ash tray. I would try unhooking it and moving the lever it attaches to by hand as described above and see if you can get it to go to heat ony, heat & defrost, and defrost only. While you have it off see how much the lever moves from one side to the other, then compare that to how much the vacuum defrost valve arm moves. Maybe that vacuum defrost valve is bad and not moving enough to get the vent (flap) to let air up to the defrost vents.