My AC suddenly quit on my 1999 C280 and it's necessary here in GA...91 degF again today!
My trusted MB shop ran numerous tests and says the signal is being transmitted to the compressor but it's not coming on. I can turn the compressor by hand and I don't hear any grinding or noise, however, the clutch apparently won't engage.
Mechanic wants $1200 to replace the compressor and dryer.
Based on reading posts in this forum, I did try gently banging on the crompressor clutch plate to see if it would free up but no luck.
Any suggestions?

My first inclination would be to jump power directly to the clutch to make sure it isn't operable.
The thing is, you say that the compressor is free, the shop says power is going to the clutch but it isn't operating.
So, why replace the whole compre$$or when it might just need a new clutch? Personally I'd bet it's low on freon and that's why the thing ain't engaging. You don't by chance all of a sudden have the "EC" light on in the AC control panel do you?
Gilly

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Gilly,
I believe the Shop checked freon level first but was OK.
The EC light is not on.
Does that help?
Paul

Do you have a pushbutton control unit? If so, do you know how to extract diagnostic codes? That would be my first step.

I have had 4 mb's in the last year with inoperable ac, every single one took a freon charge and started operating properly. 2x the previous owners gave me the same story that mechanics had said the system needed to be replaced at a cost of 1200-2000.

I would buy a can of refrigerant and fill it. Best $25 you can spend. Likely a small leak that over time has left the system low and keeping the compressor from engaging. You will still have a leak but if it worked for 12 years you will likely get several years out of a charge.

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1981 300TD
2005 C55
2004 E500
1999 ML430
1992 400E
1998 C43
2001 SL500
1988 300SEL
1986 190E 16V
1991 190E 2.6

My friend has a 1999 C230 and it does not have the pushbutton unit, no display, just knobs. But I thought I saw someone with a 1999 say that they had the display so maybe some do and some don't. All the 1998 C's have the display...

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra