Electric Cooling Fan Switch


The electric cooling fan switch is installed into a coolant passage of the engine near the thermostat housing and operates the radiator electric cooling fans when the coolant temperature reaches a specified temperature.

If the air conditioner is in proper working order, the engine cooling fans will operate when the air conditioner is turned on, regardless of the coolant temperature. When testing the electric cooling fan switch, make sure the air conditioner is OFF.

Below the specified temperature the switch is off (open), and at or above the specified temperature, the switch is on (closed), and completes a series circuit that triggers the cooling fan relay allowing the cooling fan to operate.


Switch Installed
  1. Locate the cooling fan switch near the thermostat housing on the left side of engine behind the distributor assembly. The switch wire colors should be green and black.
  3. Disconnect the wire terminal at the fan switch.
  5. Allow the engine to reach a coolant temperature of 196-203°F (91-95°C).
  7. Using a suitable ohmmeter or continuity tester check for continuity between the two fan switch terminals. The fan switch should have continuity (switch closed) at the above temperatures. The switch should have no continuity (switch open) when the temperature drops between 5-15°F (3-8°C) from the temperature that the switch first had continuity (switch closed).
  9. If the switch does not operate within the range of the supplied information, allow the engine to cool below 100°F (37°C) and replace the switch.

Switch Removed

Submerging the electric cooling fan switch below the threads could damage the component. Coolant must be used for this test as the boiling point of water is below the temperature required for testing some of the sensors. Perform this procedure in a safe and well-ventilated area. Do not breathe any fumes from the heated coolant. Wear eye protection and use care to not come in contact with any of the heated components. Do not use a heating device that produces an open flame.

Testing a radiator fan switch is not difficult, however to do so requires some basic equipment. To properly test the fan switch, the switch-s probe must be submersed in coolant, only as far as the component-s threads. The coolant must be heated and the temperature monitored. When the coolant reaches the specified temperature, the fan switch should be closed. Testing the switch requires the following equipment:

A safe source of heat, such as a portable electric hot plate
A container capable of being safely heated by a hot plate and handling heated coolant
A thermometer safely capable of reading 228°F (109°C)
A device to safely hold the switch such that only the coolant probe is submerged into the water
An ohmmeter or continuity tester

  1. Refer to the cooling fan switch removal and installation warning and procedures and remove the switch.

Attach a 12 inch wiring sub-harness to the cooling fan switch to avoid having to probe the switch while in the heated coolant. Place the switch into a suitable holding device such that the coolant probe of the switch is submersed in a container of coolant. Make sure the container can be safely heated using a suitable source of heat such as a portable electric hot plate.

  1. Using a suitable thermometer to measure the coolant temperature, heat the coolant until the specified temperature is attained.

    Click image to see an enlarged view

    Fig. Cooling fan switch testing-switch removed from vehicle

  3. When the specified coolant temperature is attained, using an ohmmeter or a continuity tester, check the continuity between the ends of the two-wire sub-harness attached to the terminals of the switch.
    Refer to the information in this section for test temperatures and continuity results.