Dealership? Are you joking? I have more faith in the various independent Audi shops I know in the city than any stealership. 
Ross tech wiki for that code…
00819 - High Pressure Sensor (G65)
00819 - High Pressure Sensor (G65): Open or Short to Ground
Possible Causes
Wiring/Connectors from/to High Pressure Sensor (G65) faulty
High Pressure Sensor (G65) faulty
Possible Solutions
Check Wiring/Connectors from/to High Pressure Sensor (G65)
Check High Pressure Sensor (G65)
00819 - High Pressure Sensor (G65): Signal too Low
Possible Symptoms
Climate Control stuck in ECON Mode
Possible Causes
Insufficient Refrigerant Pressure
Wiring/Connectors from/to High Pressure Sensor (G65) faulty
High Pressure Sensor (G65) faulty
Possible Solutions
[b]Check Refrigerant Pressure[/b]
Check Measuring Value Blocks (MVB)
Check Wiring/Connectors from/to High Pressure Sensor (G65)
Check High Pressure Sensor (G65)
My guess is you’re low on refrigerant
Yeah either low on refrigerant or the sensor went
That’s very helpful. Thanks!
I was just low on refrigerant. All is good. Phew…
If you get low again, ask them to put some dye in it and check for leaks around some of the AC connection points. The washers are notoriously bad once they’ve been tampered with once. I know JHM puts new AC rubber washers on after installing their new lines, but if they get crimped or twisted at all they can become a little iffy. I had the same thing with mine, replaced a $0.10 rubber washer on the front condenser and all has been good since then.
Will do, thanks for the heads up.