Is any body clued up with air con systems on cars??

Mine has stopped working. I got the car regassed a few days ago. I've checked all fuses,I've checked to see if the pump clutch works(it does when I put a live feed to it).

I've found there is no live feed to the air con pump.

Where does It get it's live from? Will the live come from the engine ecu when the air con is switched on??