first what makes you think it's the compressor that you called locked up? Just the fact that it's not turning when you turn it on?
there are a lot of steps you should take before determining it's the compressor. Make sure it's getting power, make sure it has enough freon in it for the compressor to come on., Make sure the low and high pressure switches are not defective etc.
if you've gone through all those steps and you're really sure the compressor then I would probably just go new, that compressor isn't that expensive.
But there are some good YouTube videos on how to check if it's the head or not. First thing to check is if it's getting power to the compressor at the plug when you turn it on.
the clutch is just basically a big magnet. When it gets power the magnet activates and pulls the clutch in that makes the compressor turn. The pulley for the compressor turns all the time regardless if it's on or not.
and of course get yourself a cheap gauge and see what the pressure in the system is, if it's too low then it's not going to come on regardless..