WARNING: This page is about a different car, the 2003 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: HVAC Compressor Clutch Does Not Disengage - Diagnostic Table (Steps 1 - 10)
Courtesy of GENERAL MOTORS CORP.
Fig 2: HVAC Compressor Clutch Does Not Disengage - Diagnostic Table (Steps 11 - 17)