Yung pulley yung mahirap.

See, the Calsonic uses a mechanical clutch on the pulley mechanism. This clutch is what helps attach or disconnect the compressor from the pulley. But a surplus clutch will have issues... poor lubrication, stuck-up mechanisms... it's easy for a surplus clutch to break or becomes stucl.

That's why a surplus Denso is a good idea... they use a rubber clutch... and while these might conceivably degrade over time, they won't get catastrophically stuck.

You can buy clutches separate from the compressors, but having once bought three clutches in a row (all of which failed within a month) for my surplus Calsonic on my SR20, I'm kind of wary of doing this.