The maximum freon (R-12) charge on the 123 was 2.6 lbs. The factory put a underhood sticker on these vehicles detailing the charge limits for 126, 123 & 107 vehicles; the sticker should be on the cross member above the right headlamp assembly.
Freon overcharge will definitely affect system performance, as well as shorten compressor life (the W124 compressors are particularly sensitive to overcharge).
Another nightmare you may have to endure: how much refrigerant oil was added to the system during repairs? The Delco R-4 compressor circulates its oil throughout the system, as it has no sump. If the system is oil-logged, cooling will be adversely affected.
What was the reason for the compressor renewal? Was it worn or had it seized?
If it had seized, then the entire should have been thoroughly flushed and the suction manifold assembly replaced [in the 1980s M-B came out with a service advisory stating that in the event of compressor seizure, metal particles were ejected into the system;
flushing was incapable of removing all of these particles and hose renewal was thus mandated].