Electric Cooling Fan Does Not Operate

ELECTRIC COOLING FAN DOES NOT OPERATE




TYPES OF FAILURES
Bad Fan Control Circuits- The fan control circuits fail to energize the cooling fan when necessary. This may be the fault of either the coolant temperature switch or the cooling fan relay.

Power/Ground Circuit - A blown fuse or broken/shorted wire is preventing the fan from operating. A poor ground connection may reduce the performance of the cooling fan.

Bad Fan Motor - The fan motor fails to operate when both power and ground are applied. If this is suspected, always verify that an object has not become wedged between the fan blades and shroud, and is preventing the fan from rotating.

CAUTION: When checking the fan blades for free travel and spin, always disconnect the negative battery terminal to prevent personal injury.

SYMPTOMS
- Engine overheats at idle or low driving speeds.
- Engine does not overheat at cruising or highway speeds.

NOTE: With speeds in excess of 25 mph, sufficient air flow is forced across the radiator to cool the engine without the use of the cooling fan (under normal conditions).

VERIFYING THE PROBLEM
- With the engine cold, verify the radiator and expansion tank are properly filled, fill and vent if necessary.

NOTE: Low coolant level or air trapped in the thermostat housing may prevent the cooling fans from operating properly.

Thermostat Open:

- Start the engine, warm up the cooling system and verify that the thermostat opens properly.

Fig. 1 Cooling Fan Wiring Circuit:

NOTE: Refer to Fig. 1 when diagnosing electric cooling fan system.

- Monitor coolant temperature using suitable thermometer and observe cooling fan operation.
- Cooling fan should begin to operate when coolant temperature reaches approximately 191-197°F. Fan should stop running when coolant temperature drops to approximately 182-188°F. When coolant temperature is above approximately 220°F, the condenser fan runs until the coolant temperature drops to approximately 214°F.
- Place control in maximum cooling position. Cooling fan should run whenever A/C compressor clutch is engaged.
- Using suitable gauge to monitor underhood temperature, stop engine and listen for cooling fan operation.
- With engine stopped and underhood temperature above 220°F, cooling fan should run for a maximum of ten minutes or until temperature drops below 220°F.
- If system fails to operate as outlined, inspect fan circuit for blown fuses, loose connections and damaged wiring, and repair as needed.
- If fan circuit wiring is satisfactory, test components individually and replace as needed. If all other components are satisfactory but system still does not perform as outlined, replace timer module and recheck system operation. Do not attempt to perform resistance measurements between module terminals, as timer module may be damaged.