WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Diagnostic Table (HVAC Compressor Clutch Does Not Disengage) (Steps 1-4)
Courtesy of GENERAL MOTORS CORP.
Fig 2: Diagnostic Table (HVAC Compressor Clutch Does Not Disengage) (Steps 5-17)