It sounds like yours is engaged all the time. There should be a little gap (at most 2 mm) between the front plate on the compressor, and the pulley behind it. That front plate is spring-loaded, so the compressor clutch engages or disengages, depending on whether there's current being sent through the coil behind it. You can check to see whether it works or not by dis-connecting the wire at the top of the compressor, and then applying 12 volts through it. Run a positive lead (+) to that wire, and negative (-) to the compressor housing. The gap should be closed when the current is applied, and open when no current is applied.
