Truck Repair: cummins m-11 fan clutch, fan clutch, clutch fan

Question
I have a 2000 Volvo with a cummins m-11 engine. Where can i find any information on troubleshooting and replacing the fan clutch?

Answer
Fan clutch is not a complicated device.Requires air to engage which is done by an electric valve controlled by the ECM.Meaning some sensor tells ECM to turn fan on,ECM supplies voltage to electric/air valve and air goes to fan clutch & engages clutch.Running the A/C is the simliest way to check fan circuit for working properly if it is warm outside.What is it doing exactly?