ideally this should be checked my an expect but there are things u can try yourself.firstly is the compressor going round when ac is switched on,it will be a click when u switch it on from engine bay when running and normally located on the bottom of the engine.secondly youd want a thermometer in the air vents and switch ac on its coldest setting and see how low the temp drops.
thats just a couple of things im sure others will come up with some other ideas