well, Im trying to get the truck ready for winter, I figure Ill need a defroster when its -30 below. The heat and defrost buttons dont' activate anything, but when I push the vent button, hot air blows out of the heater ducts but not the defrost. I figure the heater core is still good, maybe I have some crap in the hvac box. I was looking for some suggestions before I remove the dash or cut into the box.

 

Remove the glove box door and the vacuum servos will be visible.
pull the lines from the servos and check with a vacuum guage.
I have also seen the doors in the HVAC box become sticky because of rust on the hinge shafts.

Here is more info about the HVAC box

https://www.dieseltruckresource.com/....html?t=248580

 

The previous owner of my truck piled stuff on top of the dash. I was shocked with what I found in the defroster ducts. Pens, penciled, loose change, paperclips, stamps, assorted scraps of sticky notes, Indian arrow heads, and an 1800's BIA burial ID tag, catchup and mustard packs, rocks, leaves, pine needles. And then there was the carpet. YUCK!

 

WOW! A guy could have a helluva time in Vegas with all that stuff!
No bottle of Ol' Harper?