Australian Car Repair Issues? Ask an Auto Mechanic for Answers ASAP
More than likely low gas, so a leak should be evident, under a UV test light.
The low/high pressure switch disables the compressor if either low or high pressure exists.
Was the A/C system only marginally cold and now not working at all?
Do both radiator fans operate with A/C on?
If compressor is on initially, and both fans aren't on, you need to chase why the second fan is not on.
Or possibly an A/C pipe has been damaged when the radiator was replaced and now you have a low gas charge.
Have you found anything wrong on your car as I have suggested?