OK, after a long while I finally fixed the A/C always on problem. I received a used heater control unit (which is the unit on the center dash that has the three knobs for the fan control, vent settings and heat control) from a business on eBay and installed it today. Basically I removed the center dash cover panel (using nothing but my fingernails), disconnected the wiring harness for the digital odometer, removed the starter switch trim piece (also with my fingernails) and then unscrewed the heater control and the cubby hole below it (four screws). I then removed the heater control wiring harness and attached it to the new heater control and then reversed the above procedure to button everything back up. Your mileage may vary on what you need to get the center cover panel off; you might need a plastic putty knife or something (don't use metal as it will probably scratch your dash).
I tried to find the heater control at junkyards but didn't have any luck finding a decent 2004 or later GP with the exact same heater control I have in my car. So eBay basically saved the day for me, for $40 and a few minutes of labor I can now turn my A/C on and off from the dash. Yee haa!
