Aircon suddenly stopped working

[TriNode]

The aircon was working in my GFs K12 (she's had it only a few days, private purchase) and today it worked, but on the way back the light wouldn't come on, you hear a noise from the engine bay like the compressor runs for a second or so when you press the AC button, but that's all, doesn't seem to be working.

Any ideas?

- A