Just poking around under the hood of my 89 crew cab. I notice the plug is disconnected on the compressor. I hook it up and flip on the air, and the belt just starts to squeel Can you replace the clutch on the compressor without opening the system? I idon't know if the R-12 is even charged, but if it is I would like to just try and replace the clutch. Can a shop check the level of refrigerant in the system?