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?

Asked by for the 2001 Audi Allroad Quattro
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?