Because I could not get hold of my local specialist before a 550 mile drive and the aircon didnt seem as cold as it was I figured top up the aircon with one of those cylinders from Halfords. Connected the gizmo looked at the gauge yup slightly low. Did what it said, engine running aircon on max cools and all apeared to be going as it was supposed to. Nearly got the needle into the right zone but thought stop there and drive it and see how it is. Half a mile later smoke coming from under the car. Bonnet opened and sparks and flames shooting from the slipping aircon clutch. Switch off quick let it cool down and drive home to tell Halfords what just happened. I assumed that my compressor had now siezed and the black death I read about here had now struck. The clutch rubber bushes were all but burned away but the aircon compressor still turned when cold. Restarted it and switched to auto - yep still working and cooling fine. Tried upping the revs to 2000 then next time the clutch tries to cycle in it slips again. Result econ and no cools for the next 2 weeks and 1500 miles in 30c heat. Expert on the aircon top up gas explains no way it could have caused my problem. So was it a pure coincidence with the way aircon problems happen with this car? I began to imagine that maybe I actually overfilled it even though the little guage said there was more to go to be in the correct zone pressurewise on the LP side.

Got home acquired a new compressor. Aircon man pulled out the gas. I took the old one off and looked inside the ports expecting the worst. Findings, spotless inside oil clear as water. compressor turns smoothly but the pulley bearing is now quite tight after the roasting from the clutch. At least there does not appear to be debris in the system

New compressor is on and refilled today and so far seems fine but I havent driven it on the roads yet. I noticed on the professionals guages how much the low pressure side pressure varies while the cooling cycle operates. System seems to test out healthy. It could well be that in trying to reach the pressure on the refill canister it could be overfilled.

What happened to the old compressor and clutch to lock up the clutch?

Mystified and down a few hundred getting chilled again!