I'd try what was suggested above, then before spending $$ to swap out parts randomly, check the ECU and climate control computer operation. The climate control system sends a signal to the ECU, which in turn draws the wire to the compressor clutch to ground to engage.
Reaper has an FTP site (
http://reaper450128.homeftp.net/servicecd.htm) with two files that need to be downloaded to troubleshoot the system: a) Automatic Climate Control (troubleshooting and computer voltages), and b) J-Pin Voltage Charts (this has the ECU signal line voltages).
If it turns out to be an ECU problem, I can help. It's relatively cheap (less than $5), but it requires wiring surgery and you lose the ECU cutout of the compressor during WOT - I would prefer you look around for a used ECU - I found one locally for $45.