Fan Clutch Question

Russ Knight

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Perry, FL
The fan on my truck engages automatically when first starting for about 15-20 seconds, then disengages. With the air system pressurized, engine off, key on, when engaging the clutch manually, the fan physically moves in towards the engine. However, when sending air manually with the engine running, fan will not engage. Truck has yet to get over about 190 when running, but I have never heard the fan engage at any other time other than when first starting. Any ideas?
 

Elijah95

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Georgia
For future reference, there is an air solenoid up by your horn solenoid with a red circle and a slot in it, you can take a small flathead (think glasses or control screw driver) and manually engage the solenoid to test run your fan.

The MTVR uses a improved system over the old M939 5 tons for engaging the cooling fan clutch by essentially locking the fan in if the truck loses air pressure allowing the truck to still limp out of a bad situation if needed without overheating when air is lost whereas the old M939 trucks would lose the ability to engage the fan clutch if air was lost.


Sent from my iPhone using Tapatalk
 

Russ Knight

Well-known member
Steel Soldiers Supporter
970
669
93
Location
Perry, FL
For future reference, there is an air solenoid up by your horn solenoid with a red circle and a slot in it, you can take a small flathead (think glasses or control screw driver) and manually engage the solenoid to test run your fan.

The MTVR uses a improved system over the old M939 5 tons for engaging the cooling fan clutch by essentially locking the fan in if the truck loses air pressure allowing the truck to still limp out of a bad situation if needed without overheating when air is lost whereas the old M939 trucks would lose the ability to engage the fan clutch if air was lost.


Sent from my iPhone using Tapatalk
Yes sir, that assembly has been replaced with a brand new one. I just did not know the fan engaged when the air supply was cut off and vice versa. Makes sense to do it that way. Thanks!
 
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