A/c Compressor Or Clutch?

The A/c On My Truck Quit Working This Past Weekend. It Blows Like It Should But The Compressor Will Not Engage. With The A/c Switched Off, The Outside Pully Turns Like Normal And The Inside Clutch Does Not Turn. After You Engage The A/c Switch Inside The Cab, The A/c Clutch Turns But Very Slowly And Not At Near The Speed That It Is Supposed To While Engaged. Does This Indicate A Bad Clutch Even Though It Will Partially Engage, Or Is This A Sign Of Another Problem With The Compressor.

A Side Note: The Truck Has About 160,000 Miles On It And The A/c Has Worked Great Until Now With The Exception Of About The Last Few Months (the Hottest Time Of The Year Here In Texas (temps In The 100's)). The Last Few Months It Seemed Like It Took It Longer To Get Cool In The Cab But After That Initial Cooling It Worked Like Normal.

If the system is low on freon it may cause this condition you should have dye added to check for leaks and refill system before throwing parts at and spending a small fortune..