Defrost Problems

[crawdad]

There is a second one I believe. It is near the center of the dash in between the glove box and the radio, somewhere in that area. It is concealed by the duct work. Take the bottom duct work off and look up under there and you'll see it. It's near or on the end of the main heater box, for lack of a better way of describing it. If I remember correctly, that is the one that controls the defroster. At least it was on mine. If I can find a schematic, I'll post it for you. HTH

[Phuloi68]

there are two things, assuming all your vacuum is intact and original, that causes most defroster issues.
The rubber hose coming off the t right behind the carb cracks with age and heat and the heater flapper door has a little white plastic piece that always breaks on the older trucks. My guess it is one or both of those items.
Do a search on the general forum (I think) and you will see a couple of pics.