[kuehl]

Clutches: things that fail on clutches:
a) the pulley bearing when either it has alot miles on the compressor, or if the compressor overheats it reduces the viscosity of the grease in the bearings,
b) the rubber laminated front clutch it has alot miles on the compressor, or if the compressor overheats it toasts it, like a severe friar's roast,
c) the clutch coil winding breaks or shorts because either the compressor overheated or either of a or b above

Compressors: things that cause compressors to lock up or freeze:
a) overheating due to high system pressures,
b) lack of refrigerant oil flow due to low system pressures or simply too little oil,
c) too many refrigerant top offs over the years and failure to add oil
d) the compressor is worn out from any of the above or too many miles and years of use
e) not following directions

You'd best off considering getting a new compressor, drier, o'rings for the system, have the lines and condenser flushed properly. Inspect the lines that have rubber.
Insure the fans operate properly.