1986 A/C-Heater air flow, not right

1986 F-250 6.9:
A/C - Heater control on the dadh no longer allows air to defrost/floor/mix (maybdodoe mix?) I don't use A/C (disconnected the belt).
All was working as it's suppoed to. Then last week, when moving the arm/lever for defrost/mix/floow/vent, all that would come out was air blowing on each side of the dash an next to the glove box! Not good, especially with cold weather approaching.
I bought a Motorcraft A/C - Heatrer Valve (E1AZ-19B999-B, small town Montana Ford dealership had one in stock - since 2010).
Did the change out of that part (oh what a wonderful time that was) and no change to the condition of only blowing air on each side of the dash and next to glovebox.
Most likely some sort of vacuumn issue?
There is a small vacuumn tank(?) to the left of the glovebox. I'm not familiar with all it does, and of course there are vacuumn lines to be scouted out.
Any suggestions would be most helpful.
I'm no major mechanic, but do some and always willing to dig in n' give things a try.
thank you...

Not sure your exact issue, but I've rebuilt my entire AC/Heater system and can tell you the issues I found.

The blend door itself had hinges that were damaged, so I made my own hinges. The rear of the heater/AC control panel had a rubber block that all of the vacuum lines attached to which was then plugged into a vacuum switch of sorts. This switch leaked, I went to the junkyard and robbed 2-3 and the first one functioned for me. Past that it was just a couple of general vacuum leaks from old lines.

Circled the offending switch in blue, it is the tan piece that the rubber vacuum line connector plugs into. Some of the prongs had cracked, probably from less than careful handling on my part.

Thank you for the input/suggestions.
Now to scout out pieces n' parts...

I'll throw in my 2 cents worth. Typically if the HVAC vacuum hose fails, the default position for the vents is the defrost mode.
If you have air coming out of other vents then I suspect your control is broken. As for the hard plastic lines, you can repair those easily enough with rubber windshield washer hose. Get the smaller inner diameter hose, wet the hard plastic and the inside of the hose and slide it together. If you don't have to force it, your hose is too big.
Wet, ie, spit.

Here are some diagrams and info on a 86 system.

Electrical part of it.

Function description and legend for above electrical diagram.

How to troubleshoot vacuum circuits.

@BlindAmbition
I realize this is an older thread but I wasn't compelled to start my own when this was close to the same issues I'm experiencing.
A few questions. The vacuum motor I have pictured is connected to a door. Is that the blend door that you mentioned having to build a hinge for? Mine has a door attached to the rod but not fastened to any hinge so the door flops around.
In the other picture to the left of the heater core; is there supposed to be some type of door to block off any heat coming from the heater core when the ac is running so as to not have a temperature battle? The warm/ cool selector lever on the dash operates a different door which prevents the cold air from going to the duct but the hot air always seems to be open to the duct work by lack of an additional door. (Maybe I'm over thinking things)
Lastly, the picture where the hole on the heater core cover; would that be where the lever pokes through if there was some type of door separating heat from cold?
I appreciate any help since you seem to have been there, done that.

The blend door is purely mechanical with a cable hooked directly to the temp lever, just like a lawnmower throttle. See if that actuator in your picture moves when you move the lever from panel to heat.

That one moves just fine. The one I'm curious about is connected to that vacuum motor by a small lever. It seems like it's the door that varies the flow between the dash vents and the floor. Not the windshield vents. Plus that opening to the left of the heater core, where the light from the engine compartment is shining through. I'm wondering if something is missing.

The light is shining through from the engine compartment because that door you're talking about is open.

I believe this is the door you're talking about. It works from the temp lever you mentioned. I'll try to get a picture of the other door. I had to take two pictures since I'm not certain how to change my phone camera settings to get a video to upload to the site. It won't take mp4.

This picture is looking from the engine compartment through the open evaporator core housing. You can see the lever connected to that gray door; I'm thinking that should have some type of hinge connected to it. Right?

@tbowker That last picture is the door I made a hinge for. I used either a few small hinges or one strip of hinge (piano hinge?) that I cut to fit. I recall adding some sound deadening material I had laying around to fill any gaps on the hinged part.


Here is a link of what I mean - https://www.homedepot.com/p/Everbil...-Matte-Black-Continuous-Hinge-28806/314151799