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?
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Those doors are notorious to break and then flop around; and, once broken, you have little if any defrost air movement.
For the current time being, I have my broken door completely removed.
When I know summer is here to stay, I have a piece of "eve flashing" (super-thin Aluminum that builders use to trim out the eves) slid in behind the glove box that I slide out.
With the sheet slid in between the two pieces of the air duct, it blocks off the dash vents and forces all the air to go either up to the defrost or down to the floor.
With the sheet slid out, almost all the air comes through the dash vents.
I have to remove the glove box to make these changes.
If I have the dash vents blocked off and it happens to get warm enough for A/C, plenty of cooling air comes through the top or the bottom, just not in my face where it feels the best.
There is an excellent write-up on how to re-hinge that broken door at fordtruckenthusiastsdotcom.
The original hinge was an almost through slice in the plastic that was a break waiting to happen; I plan to make my hinge out of heavy leather so that it will behave much like the original.