It could mean a problem with the blower motor. Could need new brushes or a whole new motor. It's pretty easy to get to the motor on a W126, but I don't know how to diagnose that it is the motor that's causing your fuse to blow. I suppose you could disconnect the motor and turn on the ACC. If the fuse doesn't blow, maybe it is the motor.

FWIW, my SE ACC fuse blew in June 2000 and June 2001. I'm waiting to see what happens in a couple of months.

Sixto
91 300SE
87 300SDL
81 300SD