Mechanical Systems Troubleshooting Procedures - Continued

Troubleshoot The High Mobility Multi- Purpose Wheeled Vehicle (HMMWV)
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Check for continuity in the fan temperature switch.

Disconnect the engine harness leads 458A and 458B at the engine

temperature switch, located on the left side of the water crossover.

Using a multimeter, check for continuity between switch leads. With

the engine coolant temperature above 215 F, the switch should be open

(no continuity).

With the coolant temperature below 215 F, the

switch should be closed (indicating continuity). If the switch does

not test correctly, replace the fan temperature switch following the

procedures contained in paragraph 4-30, page 4-49 of the TM.

Step 9. Disconnect the connectors between the fan drive solenoid and

the time delay on the left hand cowl. With the engine running, the

fan should operate. If the fan does not operate, proceed to step 12.

If the fan operates, proceed to step 10.

Step 10. Test the fan clutch solenoid. To do this, use a multimeter

and check for resistance between the connector terminals. Be sure to

check for resistance both ways. The resistance should be 75 8 Ohms

one way, and 12 1 Ohm the other way. If the resistance indicated

is not what it is supposed to be, replace the fan drive solenoid and

the hydraulic control valve following the procedures contained in

paragraph 8-20, page 8-48 of the TM. Now check the operation of the

fan with