No Aircon, cant work out electrics
 

Im tryign to diagnose an aircon fault with brothers 2006 holden rodeo (HOLDEN IN AUSTRALIA SELLS THE ISUZU RODEO)
No power to AC clutch.
The aircon relay doesnt click when i plug it in or unplug it, replaced with known workign relay with same result.
Anyone able to shed light on how the system works,
THe LED on the switch in the cabin lights up when pressed, so i wouldve thought that means the switch is getting power which would mean the switch is turning on and off the relay, but that isnt the case .When key is off there is one 12V positive coming into the relay holder. When key is turned to ON, there is another. So i then assumed maybe the aircon swithc grounds the negative side of the relay swithc, but no, this isnt hapening. so either, Im wrong in my asumpton that the switch grounds the relay, or the switch does ground the relay, but also sends the power on somewhere else like a thermostat or somethign.
The car doesnt have climate control, jsut a button and a heat/cold selector.
I jsut dont know how the system works, and dont have money to pay an auto elec.