If your car has AUX cooling fans, I would check those. I would not recommend replacing any mechanical components before the electrical systems have been checked out.
In general, in a W124, AC compressor is usually turned on and off every 20 secs if the engine is overheating and to prevent AC components from freezing.
There are numerous senors in the AC system which can also cause a problem, but the AUX fans seem like the most likely cause.
Does the engine overheat while the car is stopped?
94 E320 58000 Miles