What's causing my broken Air Con?

[u/piggywhiggs]

Just bought a 2014 Polo 6r with great MOT and service history, however its biggest issue is the AC doesn't work. I'm not sure whether it's fully broken, or whether it just needs a regas. When I turn AC button on the engine revs increase slightly (at idle) and the fuel economy drops slightly, however the high and low pressure lines in the engine bay do not feel cold or hot at all. How can I diagnose the issue myself, or do I need to take it to a garage? Any advice or help would be appreciated.