You did let the car idle for a little while waiting for the fan to kick in? It will only turn on when the temp gets to a certain point (around 213 degrees or so).If it does not turn on past this point yet it will turn on with the A/C engaged then your ECT (Engine Coolant Temp ) sensor is faulty.
Try this test.Start the car.Now under the hood,look behind the ignition coil pack.Theres 2 sensors back there.The ECT sensor is the one with 2 wires (NOT the one to the right with 1 wire,thats your temp gauge sender).With the engine running,unplug the 2 wire sensor.The fan should kick in a few seconds after unplugging it ...then shut off once plugged in.
Do you have an ohmmeter? Something you could use to check for resistance and voltage.