Hey Manta928 - You should do a thorough search on the 928 A/C system before replacing any components. I agree with Neil when it comes to letting someone make a "shoot from the hip" troubleshooting suggestion on a 928 without an extensive knowledge of the vehicle.
The A/C system is not terribly difficult to understand but there are definitely a few specific areas to check and verify well before replacing the expansion valve. Keep us posted on your progress.
Good Luck, Michael
