GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Jimmy - 4WD 🢒 HVAC 🢒 Heating, Ventilation and Air Conditioning 🢒 Fan Clutch Diagnosis

Noise

Sometimes fan noise is present under the following conditions:

    • The clutch is engaged for maximum cooling.
    • The noise is present the first 15 seconds to 1 minute after start-up. This condition occurs until the clutch can redistribute the silicone fluid to the normal disengaged operating condition (after settling 2-4 hours).

Fan noise or an excessive roar generally occurs under all high-speed conditions (2,500 RPM or higher) if the clutch assembly is locked up due to internal failure. If the fan cannot be rotated by hand or there is a rough grating feel as you turn the fan, replace the clutch. Refer to Fan Clutch Replacement .

Looseness

Inspect a loose fan assembly for wear. Replace a worn assembly as necessary. Under various temperatures, there is a visible lateral movement at the tip of the fan blade. Allow approximately 6.5 mm (1/4 in) maximum lateral movement measured at the fan tip. More movement is cause for replacement.

Silicone Fluid Leaks

Small fluid leaks around the bearing assembly will not affect the fan clutch operation. If the leakage appears excessive, replace the fan clutch. Refer to Fan Clutch Replacement .

Engine Overheating

Inspect for engine overheating as follows:

  1. Start with a cool engine to ensure complete fan clutch disengagement.
  2. If the fan/fan clutch assembly free-wheels with no drag (revolves more than five times when spun by hand), replace the fan clutch. Testing a fan clutch by holding the small hub with one hand while rotating the aluminum housing in a clockwise/counterclockwise motion will cause the clutch to free wheel. This is a normal condition when operated this way. It is not a test to determine replacement.
  3. Position a thermometer between the radiator and the fan blades. Do this by inserting the thermometer sensor through one of the existing holes in the fan shroud, or by placing it between the radiator and the shroud.
  4. With the thermometer in position, cover the radiator grille enough to induce a high engine temperature. Start the engine. Turn the air conditioning on. Run the engine at 2000 RPM.
  5. It takes approximately 5-10 minutes for the temperature to become high enough to allow engagement of the fan clutch. This will be indicated by an increased in roar in the fan air noise. There also will be a drop in the temperature reading, from 3-15°C (5-15°F).
    6. • If the clutch does not engage between 65-90°C (150-195°F), the fan clutch should be replaced. Be sure the fan clutch is disengaged at the start of the test.
    • If the fan noise level is constantly high from the start of the test to 88°C (190°F), without any noticeable noise level increase or drop in temperature, the fan clutch must be replaced. To prevent engine overheating, discontinue the test, past a thermometer reading of 88°C (190°F).
  6. As soon as the clutch engages, remove the radiator grille cover. Next turn off the air conditioning. This will assist in engine cooling. Run the engine at approximately 1500 RPM.
  7. After several minutes, the fan clutch should disengage. There will be a reduction in fan speed with decreased fan noise. If the fan clutch fails to function as described, you must replace the fan clutch. Refer to Fan Clutch Replacement .