I think I now know the reason my Uncle had the dash apart !! I bought this 84 F150, straight 6, a week ago. I have been doing a lot of small maint items ever since. This weekend I tried the heat controls, and you know what?? Everything seems to come out of the vents, heat, defrost, etc. Can anyone give me some ideas of how to correct this or at least the most common areas to look??

Thanks !!

 

One of the "doors" that open and close directing the air up, out, or down, is either stuck/broke (most likely.....welcome to the club) or if you're lucky one of the vacuum lines running from the control is leaking. Or one of the vacuum "motors" is shot.
This can be a very labor intensive fix, either for you or a shop.
My recommendation.....praise God you've got any heat at all, and leave it.

 

IN my 84 f-150 a vacuam line had can off behind the radio bezal also check the vacuam in the enginge carpment goning to the firewall. I have also seen leaves, pine needles, paper plastic bags, and nurmois other item suck in the vents keeping doors from opening.

 

This problem is fixable. I also have an 84 F150 and it is probably the flapper hinges that are broke. It is a pain in the neck to fix but i can tell you one way it can be done. First you need to check the vacuum system. The vacuum comes from the small black line in the engine compartment above the blower motor. This is the door vacuum motor that lets heat in to the cab the line dissappears into the cab and goes to the heater controls. under the dash is another vacuum motor for the flapper.This motor is just to the left of the back of the glove box under the dash. when you move the heater controls to the right the vacuum motor should extend. This does not mean the flapper is working. To see whats going on you remove the glove box then under the glove box is a plastic cover that housed the heater core. Unscrew it and with a flashlight and a mirror you should be able to see the flapper up in a hole to the left.
When you turn the heat on you should see the vacuum motor for the heater move. The heater core on these trucks is always hot.When the door opens air flows thru the core into the cab. Ford started the construction of this truck with the flapper and built the truck around it.It takes about a full saturday to fix it and some of the time two people are needed.
If the hinges are broke let me know.