Mercedes Benz Air Conditioning Compressor

First of all, some compressors just wear out. You put a bazillion miles on them and their time is just simply up. However, the majority of the time the compressor fails is from lack of proper maintenance or the result of poor service procedures.
Let's remember that most of the A/C compressors that Mercedes Benz have used do not carry their own onboard 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.

Ok, now you realize your Mercedes A/C compressor is kaput so let's fix it right the first time. No use crying over spilled milk. The key now is to get you cool again and make sure you do not have any more problems.
Do not just bolt up another compressor without trying to analyze why this one went bad. Check for signs of leaks and make sure the auxiliary fan works. If the compressor clutch is white or shows signs of being subjected to extreme heat you can figure the compressor was intermittently locking up. This is due to lack of lubrication or internal breakage or both. Whatever the reason, shrapnel from the compressor was introduced into the system. Failures to remove this shrapnel will grenade your new Mercedes compressor. This is not covered under the warranty.
You must change the receiver drier when changing your new compressor. Just consider the receiver drier the oil filter for your air conditioning system. Some of that metal will be found there. By the way, if you do not change the drier the manufacturer will not warranty the compressor.
Another item that we recommend changing at this time is the expansion valve. These for the most part are easy to change and very inexpensive. The expansion valve allows the refrigerant to be sprayed on the evaporator. The orifices are very small and easily clogged by debris. You are not going to clean the valve so just change it now so you can assure yourself that when you install the new components described above the system will blow really cold air. It is a shame to redo the whole recharge over a part that costs approx $25.00 for many applications.
One last thought. If you are going to use a refrigerant other than what came in your vehicle check to make sure the refrigerant temperature switch you have installed on your drier is the right one for the refrigerant you are using. R134a uses a different switch than R12. The switch with the pigtail is the refrigerant temperature switch. These are temperature switches not pressure switches. Different refrigerants operate at different temperatures so double check your application.
Ps: It has been our experience that when the clutch is bad on your Mercedes compressor, it failed because of the scenario above. Don't waste your money just replacing the clutch. Change the compressor. We can argue that point till the cows come home but that is our opinion and we are sticking to it. We have seen to many people try it and lose. Why take a chance, besides when you see the price of a clutch versus the price of a compressor with a new clutch it becomes a no brainier.