I just picked up my '63 Series 62 from the shop yesterday, after it spent 51 days there for repair of various oil leaks.  Started it up and turned on the A/C, it ran great for about 30 seconds and blew cold air, but then the compressor started screeching loud enough to bring people running out of the shop.  My mechanic looked at it for short time, rotated the clutch back and forth for a bit, and things were okay again. He thought it may have been from sitting too long.  I got about 3 miles down the road and it started screeching again. Same deal again this morning.  The noise starts when the clutch engages.  The belt is not slipping.  Any ideas what I am up against?  This is a 34,000 mile car, so the A/C components are all original equipment. Thanks!

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The belt may not be slipping, but the clutch might be.  The clutch will wear away over time or get grooved, and then stop holding.    Start off by checking the air gap between the clutch and driven section of the pulley.  It should be 3/32" according to the 64 shop manual,  and it can be adjusted in or out using an AC clutch installer tool.   If adjustment doesn't eliminate the problem, replace the hub and clutch or the whole compressor.   
It could be an internal compressor issue, but that is usually a knocking or grinding rather than a screeching.  You can spin the compressor by hand by turning the center hub with the engine off, and if you feel roughness, then it could be the bearings or the 'gut pack' in the compressor so it will need to be changed. 

Thanks for that info, Mark.  I checked the '63 shop manual and it says the air gap should be 1/32 to 1/16, and mine is within that range.  The center hub also turns smoothly when turned by hand.  I'm leaning towards just ordering a clutch plate and hub assembly to start with, as it can be replaced without removing the compressor.  Looks like there are many after market ones available on line that claim to fit a '63 Cadillac compressor.  Mine is a Frigidaire model 5910438.  


disconnecting the electrical harness from the compressor

It  should prevent the clutch from engaging the compressor  thus stopping the screeching until you have time to address the  actual problem you are having with the AC compressor clutch ?

just a bandaid until the problem is addressed and the screeching  noise is under control until you fix the problem 


Tony and Ginny 429, I always turned off the A/C at the dash control as soon as it started screaming.  But I did take your advice and disconnect the compressor harness this morning, and found out that I can still get outside air through the A/C vents in the car, so that was definitely a bonus. Prior to doing that the only way to get outside air (with the A/C turned off) was to switch the control to heat, but on the coolest setting.  The only problem is that the air came in through the floor vents, which wasn't much help. So thank-you for the suggestion.   

Glad my suggestion worked out for the best 


on my 73, it was the bearing, I replaced it, and it stopped,, 



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