Late Build 08 Charger PCM Pinout?
 

Got a 3.5L SXT RWD
I believe it should have same wiring as a 09 Charger. Getting code P0645 A/C clutch relay, absolute last thing to try is tracing the signal wire from the PCM to TIPM have had no a/c for about a year now.

Get a factory service manual for your car. That will have all the wiring diagrams you will ever want. (and then some..... :) )