Fan Clutch Tutorial - Part 3 Replace the Fan Clutch and Water Pump at the Same Time How to Detect a Faulty Fan Clutch Fan spins excessively when engine is stopped. Poor A/C performance at idle or low vehicle speeds. Fan speed does not increase when engine is hot. Fan speed does not increase until engine is excessively hot. Fan blade tip moves more than 1/4” front to back. Fan turns roughly or does not turn at all. Excessive fan noise at all speeds due to failed bearing. Vibration that increases with engine speed.