replacing the clutch is not a good investment. look on Ebay and get a rebuilt compressor for about $120.Before anything else, check for leaks. If none found, Replace your old unit,recharge your system and feel coolairo!!
Here in South Texas, we know AC!
el raidman

when the freon level drops below a certain amount (pressure) the cut-out switch turns off the power to the compressor. I think you are only low on freon. Go to Frantic-Boys, buy a pressure gauge for the AC. Follow directions and add a can of R134 to your system and the BLISS will return.
el raidman

No fun in the heat.

First, read the following post (http://www.brickboard.com/RWD/volvo/1363079/220/240/260/280/ac_clutch_lesson_tonight.html). In effect, it says to check whether the compressor's ground wire is still doing its job. If it isn't, you will get the symptoms you describe.

Also, if your refrigerant pressure is below acceptable levels, an interlock switch will prevent the clutch from engaging--but in that case, you would probably not get the 12v you have observed on the green wire.

Finally, I believe the clutch can be changed in the car. IF no one else answers, do some googling, and you will find that a special tool is needed to remove the old clutch, but it is affordable. And it is not universal; you need the correct one for your compressor make and model. Volvo has used Sanden rotary compressors, and maybe some others.

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jds