An electric radiator fan only starts spinning once the engine reaches a preset operating temperature. To test it properly, there are a few steps that should be taken to ensure all the components are checked. These steps require a moderate amount of mechanical knowledge.
The first thing to check is the fan motor. This is done by unplugging the radiator fan from its connector and applying 12 volts of power directly to it, along with a ground. This can be done using jumper wire from the battery. When this is done the fan should spin and there should not be any strange noises.
If the motor works, the next things to check are the relay, fuses and wiring. This can be done by switching on the car and immediately turning on the air conditioning as high as it will go. If the fan runs, all of these components are okay, leaving one more to check.
The final component to check is the temperature sensor. The easiest way to do this is to let the engine warm up to a normal operating temperature. This is not an instant check, but it can be done by leaving the engine idling for a period of time. When the coolant temperature reaches somewhere between 200 and 230 degrees (depending on the car) the coolant fan should automatically turn on.