AC compressor on an old old mercedes and alternator


OK, so we just bought a lovely 71’ mercedes 250 C. …with 60,000 miles. The AC needed to be recharged with R12 which was expensive but we did because it was 108 degrees down here in Texas. We got it recharged, still had 1/2 a charge to it, and 4 days later quits on us. We start the car, let it sit for a minute because just carburettors, makes a very loud noise like some one is shoving a crow through a paper shredder, and the whole car dies. We tried that a few times and now the generator light won’t shut off when we are driving and the car handles rough and is very rough to start up. We where told by a mechanic we trust that the compressor was probably out on the AC. Which means now we have to shell out $1,100-$1,700 to have the AC converted to R134a, since no one makes or can find a compressor for a 40 year old mercedes for some reason.

My real question is this. The AC is dead to me for now, we will deal with it when we have the money, but what about the roughness and the generator light? Over the phone, the mechanic says alternator. But the alternator and most of the car was just fine before we had the compressor problem. Should we have been warned about any of this happening by the mercedes dealer that we took it to to have the AC recharged? Also, is the AC dying and the alternator going rough on me somehow linked? We are assuming we will have to get a new or rebuilt alternator, if not now then very shortly. We know the AC is linked by a belt to the engine and the dealership told us about that, but a dead compressor and a dying alt were not brought up. Should we be worried in a few months when we have the AC retrofitted?