How could it be a fuse if the fan works now and then? if the fuse blew it would not work at all right? Is there some sort of relay module that controls the fan? maybe its bad. I once had a bad power window motor in a 280 Z a few years back, it would roll up a bit then stop. if I waited it would do the same. it turned out the motor was so worn out of tolerances that it was triping a "breaker" type of device that would reset itself. just some thoughts...

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1996 E320
2000 C230 Kompressor
1988 190e 2.3 - 225K miles, owned for 7 years. I cannot say enough good things about this car. Very well built, even at 225 it ran like new.