Fan clutch troubleshooting tip.

Dear Half-Mast,

What's with the fan clutches for M939A2-series 5-ton trucks? When the Fan clutch won't engage, I thought the right thing to do was to replace it. But the replacement clutch still won't engage. How can I fix this?

SSG Y.M.E.

Dear Sergeant Y.M.E.,

You're not the first soldier to complain about brand new fan clutches being defective. Things aren't always how they seem, though.

Take a look at Item 7 in Fig 121 of TM 9-2320-272-24P-1. This elbow, NSN 4730-01-315-5596, could be the key to unlocking your troubleshooting door.

The elbow has a tiny metallic screen inside of it. If the fan clutch doesn't work, this 90- degree elbow fitting at the supply air line to the fan clutch may be plugged. See if either cleaning the screen or replacing the elbow gets the fan clutch to work.

If the fan clutch still doesn't work, eyeball the fan clutch actuator, NSN 2930-01-285-5027, shown as Item 6 in Fig 121. It has another small metallic screen inside of it. Make sure that one isn't plugged, either.

If your problem still exists after both screens have been checked, go ahead and replace the fan clutch actuator. That ought to get your cooling system working properly again.

You can test the operation of the fan clutch using the guidance on Page 4-376 in TM9-2320-272-24-3.

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