A/C - does naff all

[clonmult]

Had my A6 (01 TDi Avant) serviced a couple of weeks back, and asked them to do a once over on the A/C - I'd switch it on, and I got a god-awful humming from under the bonnet.

That sound turned out to be some fan that had split in two, replaced and they said "It should be okay now". It didn't actually get tested on the day.

However, come along to a nice sunny day, switch on the A/C, and it does, er, nothing. Its been pressure tested, all gassed up nicely, but the air just doesn't change temperature.

Before I go back to the garage (local VW/Audi independent) and splash a load of cash, any suggestions on anything I could maybe look into myself? I've done a basic check on fuses, but they all seem okay. A/C gas was pressure tested prior to the service, and that came back fine.

[OldSkoolRS]

Does it get hotter if you turn the heat up? I had a Vectra once that had AC and one of the flaps that control the airflow lost a linkage and it meant the temp wouldn't change. I don't know if the Audi is similar, but it might be worth a quick check before hading a bundle over to the dealer.

[Tame Technician]

Failed compressor probably if your SURE its got gas in it.