Can you identify the fuse for the AC or heater circuit? Don't just look at it, swap it with a fuse of the same rating from a circuit that works, or a new fuse.

It's probably not a bad resistor pack if it doesn't work in max. Sounds like the blower motor needs new brushes, bearings or flat out replacement. Hopefully it's the same motor as US 201s.

Sixto
87 300D