If yours has enough gas in it then there’s not a huge amount to go wrong short of complete failure of the compressor. There is a plug to the left of the radiator just inside the engine bay. Unplug that and make sure it’s not all crusty. Check the fuses if you haven’t already.
I have an old post from @Roadster_Robbie off the old board saved on my PC which I have just managed to find on the new board:
post number 7 is very useful much like most of what @Roadster_Robbie says 
Hope that’s as useful to you as it was to me