1987 Thunderbird 3.8 I get air through the defrost and on the floor but nothing else.
I replaced heater core last fall and do not recall taking any duct work apart, the fan only blows on high I have been told that a thermo reactor or something like that is bad.
See HVAC vacuum diagram.
The thermal limiter on the blower resisters has blown. Rockauto has them.
https://www.rockauto.com/en/catalog/ford,1987,thunderbird,3.8l+232cid+v6,1140220,heat+&+air+conditioning,blower+motor+control+module+/+resistor,6557
its just a fuse,, that blew but this special fuse is made onto the blower speed controll thingy inside your duct behind the glove box.
it can be jumped with a really super thin wire half the diameter of telephone type wire or something small you have lying around.
your just trying to recreate a fuse link again but doing so with the idea that the wire you pick will in fact blow....
clean the squirril cage / fan blade out,, its probably heavy crud build up and making the motor work hard.
lubricate the shaft again,, if i recall, there is one of those "oil here" ports on either end.