1993 300D 2.5 Turbo W124 161K miles:

My AC compressor is off, I have checked all fuses, including strip fuse, belt is good, climate control works, blowers are working, clutch turns by hand, what else should I check??
Thanks

__________________
2000 Ford 7.3 Powerstroke 4x4
2006 Mazda Tribute
1983 Black 300 D (donated to charity)
1993 Teal 300 D (160K) Sold
"I love the smell of burnt diesel fuel in the morning, it smells like ....VICTORY"

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USMC 1973-1976

In your reciever drier unit (the sightglass), there is a low pressure cutoff switch. The purpose is to not energize the compressor if the freon level is low. It prevents burning out the compressor.
If you unjack the plug from the drier and put a jumper across the 2 wires with the car running and climate control set for a/c you should hear and see the compressor click on. You probably need to charge up your system a bit. I have seen only an ounce or two low will cause the pressure switch to remain open and not give you a/C.
Incidently, When you recharge a system from zero say after you did a repair, This is how you get the system to draw in freon. HTH Mike

If the system has been de-pressurized you will need to draw a vacuum on it before you charge it with freon/134. You can't just energize the clutch and draw freon into the system since it's full of air, very bad.

Low refrigerant levels will cause the system to not engage the compressor and there is a device called a KLIMA relay which will also disengage the compressor as a safety measure. There are about 3 million posts about this topic and Steve has also written an excellent explanation of how the system works on this website, check the the links from the homepage of mercedesshop and you will find them.