While the engine is off, grab a fan blade at the 12:00 position and hold it firmly. Have someone start the engine (while you are still holding the fan blade and keeping it from turning) and take the engine to 2,000 rpm's and hold it steady. Let go of the fan blade and the fan and clutch should catch up to the 2,000 rpm's within a few seconds. If it does not - then it's not working correctly.