My Audi's auxiliary fan does not kick on and the car begins to overheat on 2001 Audi Allroad Quattro

I was told this was a thermostat sensing switch. I replaced this part and the problem still exists. Any ideas what else I should look for or do I need to put it on a computer for further diagnosis?

1)How long does it take for the engine to run to hot?
2)Does the aux. fan come on with the a/c running?