The RPMs usually drop when the compressor comes on. The fan modules are known to fail on these cars. I replaced mines recently. I ended up buying a whole new fan with module from RockAuto. While I was at the junkyard, I also grabbed just the module from another CVPI to have on hand.
Current Panther: White 2007 CVPI SAP, 165k, Former State DOJ Admin Car
Formerly Owned Panthers: Gold 00 CVPI SAP and Black 05 CVPI SAP.