First of all you need to be sure that the clutch is actually engaging. Look at the compressor with the a/c switched on and check that the clutch plate engages and spins, then disengages and then engages again.

If it doesn't and you want to check that the compressor functions, then you could short the low level switch on the drier and see if it engages now. If you suspect it's low on gas then only switch on for enough time to check it engages so that you don't damage the compressor. If the condenser is the original then I suspect it's rusted away and the gas has leaked out.