Also be aware that this nut is used to set the air gap, it _won't_ " tighten up " like a regular bolt until the plate is pulled fully against the pulley face resulting in the compressor runing full time. Turn the nut only enough to set the gap.

Other brands of compressors use shims on the shaft to set air gap.

Check the voltage across the plug with it plugged in to be sure you are getting full power. You can cycle the clutch with the engine off as it is safer.