I had to troubleshoot my aircon not turning on too. A mechanic mate of mine helped me and we resolved it in less than 10mins.
First, take this little cap off and press the valve in *briefly* to check there is gas in the system.
**It's marked with an L for low, DO NOT press in the side near the radiator marked with an H, that is high pressure**
If there is gas in the system, it's either a problem with the compressor, electrics or control module.
http://www.nissanpatrol.com.au/forum...2023/04/74.jpg
My problem ended up being a dirty contact in this terminal preventing the receiver/dryer from switching the system on.
http://www.nissanpatrol.com.au/forum...2023/04/75.jpg
I cleaned the contacts in this plug with some electrical contact cleaner and it worked perfectly again!
Hopefully yours is an easy fix too!