The fan gets a solid +12v to its hot side whenever the ignition switch is on. What controls the fan and actually turns it on is either a solid ground to its other side for its highest speed, or its lower speeds through resistors that are connected to ground on their other sides. I'd #1 check that it is seeing its +12 on its hot side. If it's getting that +12v, then see if it turns on by providing a ground connection to the other side with a jumper wire connected to ground. If it doesn't turn on with a ground connection and it's getting +12v to its other side, then the fan motor is bad. If it turns on, that means trouble in either the fan speed switch or the wiring between the fan, switch, and resistor pack... and that wiring commonly overheats and melts its insulation which can cause all kinds of problems.