Hmmm... I've spent my share of time staring at the electrical schematic for the 124 air conditioning system, and I can't recall a fuse between the Klima and the compressor. I'd guess a shorted clutch coil on the compressor. It can be measured with an inexpensive DVM - I think it should have something like 4 Ohms resistance. Anything less, and it's fried.
BTW, it's impossible to determine whether the a/c system is fully charged without running the compressor. Certainly you can see if there's pressure in the system, but without actually running, it's impossible to distinguish between overfilled and barely filled.