Much obliged Gdads51. I can confirm that is the correct answer.
This morning I found out that the flapper is spot welded on and had actually popped off; it was kind of reacting to the lever moving around but was otherwise stuck in that forward position and effectively blocking off the defrost ducts. I put a hook tool in there and gave it a decent pull (but the tool was pretty light so it wasn't an abusive tug) and it fell on the floor
However, I blocked off the floor vent and PRESTO all the air now goes through my defrost vents. So although I can't switch back and forth with a cable, that'll work fine for fall up here
I'll fix that at a later date.
