Since the auxilliary fan is working when you unplug the sensor wire, I would suspect either the hi/low pressure switch is defective or you are low on refrigerant. You will need to find out what the system pressure is in order to go further. If you don't have a complete set of ac manifold gauges, you can purchase one of those self refill bottle of refrigerant with the gauge (I hope they are available down under) and connect it to the low side of the system (remove blue cap). The system pressure should register once the bottle is attached. You need at least 1.5 bar (22 psi) of system pressure, any thing less will activate the low pressure switch. You can add the refrigerant to the system without the engine running and it may be just enough to deactivate the low pressure switch. Once the compressor is running you can continue to add refrigerant. Make sure the gauge don't read more than 2.75 bar (40 psi).
I would suggest you look for a video on Youtube on how to refill or add refrigerant to an ac system.
Last edited by upallnight; 01-26-2013 at 08:54 AM.