I agree with MATT. Those are the three most likely causes.

I am a DIY, and not a professional, but I have experienced the slipping fan belt and a bad sensor...

Fan belt slippage is, in my opinion, the most common cause. Check the tension and quality of the belt. If it slips, the engagement (rotation) sensor in the compressor will sense it and "lock out" the compressor until you reset it by turning the key off and on. (Yes, sometimes it will reset after a period of time, but may slip right away and kick right back out.) Mercedes belt tensioners are quite troublesome.

My compressor engagement sensor went bad recently on my 92 SL. The "business end" of the sensor is inside the compressor, so if it is somehow dirty, it is not really anything you can take care of without draining the freon and removing the sensor. In my case, the wire from the sensor on the REAR of the compressor that runs to the 3-prong connector near the clutch had become brittle and the insulation had cracked and was shorting out the signal from the sensor. (I replaced the entire compressor.) My suggestion is to inspect that wire and make sure you have all 3 conductors (two from the sensor, and one from the clutch coil) connected to the harness at that new compressor. This style of compressor is used on many other cars without the sensor. Surely the new compressor is the right type with the sensor! On my sensor, a good reading between the two sensor wires was about 600 Ohms.

The low pressure thing is possible, but I don't know that it will lock the compressor out until you restart the car... That sensor is a pressure switch on the receiver/drier. (Closed is working, open shows low pressure.)

Leakage is about the only thing that goes bad about an evaporator. If the freon leaks out enough to disengage the compressor, it won't reset and start working when you restart the car.

Good Luck!

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02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)