I have an unco-operative selector and presently getting only Vent air unheated - doesn't matter the setting (other than def - it closes the lower heater doors but still no def).

Worked fine till today - I had a quick look around the engine comp for busted or split vacum hoses found one minor, to no avail. Had a look through the search items nothing too specific. Anyone got info?

If you've got any air blowing at all the problem is in the passenger compartment. Each of the sliding controls simply actuates a damper at the other end of a cable. They should be easy for you to follow. It's possible that one of them came loose at the far end.

The plastic gear that that lever moves may have broken. That happened to my 78 a few years back and I ended up replacing the whole control assembly.