A/C compressor acting up

[92 Arizona Towncar]

Alright... I just had my A/C recharged with R-12 this weekend, and before that I had the A/C system checked out... My mechanic said everything was fine, and I left it at that... I picked up my car, turned on the A/C, drove home, and on the way the temperature slowly went from cold to warm... I can hear the compressor kick in when I turn on the A/C and when I hit the gas, the compressor squeals until I turn it off... I've heard this before and if I'm not mistaken, it's the compressor clutch seizing up... My question is, how hard is the clucth to repace yourself, or should I have the mechanic do it, and do I need to have the R-12 discharged if I want to replace the clutch?
Just to clear things up, the compressor ONLY squeals when the A/C switch is turned "on", and then it takes a few seconds for the squealing to start...The car engine is fine, but I think something is up with the compressor... I had another fellow from another forunm say it was the belt not be tightened enough, but I'm kinda skeptical on that theory...

 

[Topcat]

I would check the AC Belt and the tension of the belt ...A loose belt will squeal and if the belt slips the AC will get warm...he may have also overcharged the system , if the system has too much freon in the compressor can lock up after it runs awhile , causing the belt to squeal..ask him to recheck the preasures , after it has run awhile..