A/C clutch will not engage

Hey guys and gals, I yet have another question for all of my Buick friends!!! I have had this car for close to a year now and never really looked into why the A/C system is not working. Now of course its that time of year here in Atlanta so I need to do something other then going down to the A/C repair shop! I feel if you can do it then DO IT. Here is the issue, Blower works for fan and heat (even on in the AC Max and other modes) But for some reason the compressor will not activate (clutch will not kick in is the best that I can say). I have checked all wires/connections and see nothing that is missing or damaged/disconnected. Now the old boy could just be shot and I am done with it but in the past with other cars I have had bearings go out and them freeze up and others that would just try to move nothing in a leaky system. Any ideas on where to start? Relays that could be bad, Fuse that is out for some reason that I don't see..... I am really at a lost in this arena so any and all help will come to good hands. This is a 91 Century Limited with 145,000 on it. I have replaced the ECU about a year ago to fix some other issues but this issues still hung around. Thanks for anything that you can give me.

-Aaron

I too have a 91 Buick Century (3.3 V6).....If your AC Compressor is not locked up (And assuming all electrical is functioning correctly), What you need to do is check the AC system for the correct pressure levels (High and low side).....If the AC System is low on refrigerant (Freon)......The "AC Pressure Switch" will not engage and and activate the compressor. Have this checked 1st! You may only need to add more freon to the system but make sure to check your label under the hood for what type of Freon your system is using (R12 or R134A).... My 91 Buick Century was the older R12 Type refrigerant.....My AC Compressor locked up (Bearing failure) and since it needed to be replaced, I flushed the entire system out with AC system cleaner (From Autozone), then installed a new Compressor, Drier Bottle, Orfice tube screen in the condensor.....Then had the entire system Vacumned down and filled with the newer R134A refrigerant at a local AC Shop.....Nice cold AC now!