xt heater controls dead

It is getting cold here in w. mi. My sort of newly acquired 85 xt non turbo auto is more fun to drive then anything but my old long departed 1964 austin healey sprite.

But those charming controls on the steering colume that set the air to defrost, heat, bilevel or vent, do nothing. My schematic makes refernece to a mode control and mode actuator. They are black boxes in the print.

Should I suspect here or are there some other common failure items?

Fortunately it is stuck on defrost so I can at least dump the dew.

tnx

rick