turbo bob1.8

Hi , had my air con re gassed about 3 months ago, it blew cold but not freezing after re gas (i think, weather was poor for weeks after) .tried it yesterday and blowing but no cold air(no different from cold on heater) light is on , and I'll take it back to kwik fit, but just wondered where I could check if compressor is working ,or any other ideas ,cheers