Hello Robert There are a couple of things with early ML's .Your aware of the fuse #44 30 amp that blows for the aux fans due to cycling. If your in a hot climate your head pressure will go to the blow off stage,cause loss of charge. "Updated aux fan harness" and 40 amp fuse. The easy way to know if fuse is blown the rear washer wont operate its on same circuit.
Also depending on last seven of the vin theres a doc about the a/c control unit on start up not controlling the air mixing flap do to low voltage causing no a/c cooling or heating.
Did you say your experiencing a vibration from blower? If so Its probably full of leaves 98 ML had a foam kit to block openings in cowl to correct debris getting into blower. good luck Tim