Hi - I recently recommissioned my AC and I learnt a bit abut the P38's system.
1. You should hear the ac compressor "click" in. If it doesn't (for some reason) the "text book !" mark will display on the panel after a few moments. If it is working, you should also see the center of the compressor clutch/pulley rotating.
2. The "ghost fans". My two fans in front of the condenser seem to come on when they feel like it. Unlike other cars, these fans don't seem to come on right away when the AC is switched on.
3. Pressure switches on AC receiver drier. There is some debate on here as to whether these can be changed with the system charged. On my car these can be changed with the system charged. There are schrader valves behind the switches, allowing you to remove them without loss of refrigerant. My three way switch was faulty which is how I know this. Apparently this is a common fault.
Hope this helps answer some questions.