Hi, thank you for your replies.
johnnyroper- The a/c compressor pull rotates freely by hand and does not seem to be doing anything unusual when being rotated by the belt.
The vibration does go away if the revs are increased slightly, so when driving the vibration is not there, just when stationary or at low revs...is this because more power is being put into the battery?
Chrispb-
The centre bolt is still in place on the compressor, the thread on it is in tact and the splines that engage the clutch plate are ok. the nut that holds the plate on is missing. ( the centre bolt is attached to the compressor and not the clutch plate, is this the same with all models?) the clutch plate its self is in tact apart from the splines that would have engaged with those around the central bolt on the compressor are worn away. I feel that the clutch plate had come loose and was chattering about for some time before the nut eventually came of.
the pully seems ok but i will check again for loosness.
i think i will replace the alternator pully, tensioner and clutch plate for good measure and see how we go!
thanks
again,
Sam