A quick check to see if the temp sensor is working, while the quad is running, unplug the wire to the sensor, the fan should immediately start running, if not, trace the wires for the fan back, there should be a plug, check to make sure the plug terminals are clean, and tight, I know a lot of Yam. Raptors had problems with loose plug contacts not letting the fan run, yours could have a similar problem. If you have a meter, ohm out the fan motor to see if it is still good, and see if you have voltage at the fan when the temp sensor is unplugged.