Let's remember that most of the A/C compressors that Mercedes Benz have used do not carry their own on board oil supply. The refrigerant oil is delivered throughout the system via the refrigerant.
Just as you would not run your engine without oil people attempt to run the air conditioning compressors without oil. How does this happen? Underneath the hood of your car is a pretty hostile environment subject to all kind of heat, cold, and vibration. Over time refrigerant may be lost through the various seals and out the front of the compressor. Since the refrigerant carries the oil it stands to reason that when you lose refrigerant you lose the oil at the same time. If you fail to replace the oil when you add new refrigerant you might as well log on and start pricing a new compressor. If you are not doing the job yourself, do not assume that refrigerant oil has been added. You must ask and make sure. It will be cold when you pick it up but not for long.
Preventive maintenance goes a long way. When you open the hood do a visual inspection of your Mercedes air conditioning system. Check your air conditioning hoses, Mercedes compressor, and Mercedes condenser for signs of leaks, that is oil residue at any of the joints or on the parts. Failure to repair the problem may damage or destroy the compressor since you are losing the oil that lubricates the moving parts of the air conditioning system.
If your Mercedes air conditioner is not working properly do not use it until you can check it out. This may prevent further damage. Remember that your compressor turns on when you turn on the defroster too so do not assume that it can wait till spring to have it repaired.