As VS indicated, you can at the very least see if the compressor is siezed by turning the forward most part in front of the pulley. This is attached to the compressor input shaft. It turns smoothly, but with smooth pulsating resistance, there is a chance that the compressor is okay.

If the belt is gone, the chance is very high that it was removed because of a bad compressor, but it's quick and easy to find out as described.

Test the compressor first, and then we can get on to the next step.

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2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

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