Last night I was driving with the a/c off and noticed a whirring sound from under the hood. I turned the a/c on and the noise stopped. The a/c worked fine for the next hour.

Today, the a/c is not working at all. I noticed that when I turn it on, there is a slight slipping noise (probably the belt) for less than a second. Then, when I look at the front of the compressor clutch, I can see it moving at about 1/2" every few seconds.

Any way to tell if it's a bad compressor or just a bad clutch?

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles