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Fan clutch wont disengage

Discussion in 'Trucks [ Eighteen Wheelers ]' started by freightlinerman, Apr 6, 2014.

  1. Apr 6, 2014 #1
    freightlinerman

    freightlinerman Road Train Member

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    Mar 4, 2011
    Florida
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    On my 91 Ford L9000 with a Series 60, the fan clutch wont disengage. The air lines are intact, I traced them around and it branches around several places. Nothing amiss. When the truck is off, the fan clutch is locked as it wont turn by hand. WHen I turn the key on, it would normally hiss, but no more.

    I'm thinking about just cutting the belt off for it, as the temperature never goes over 170 F and I don't have an A/C. Thoughts? What is causing this to not disengage? There is no working A/C on this truck either.
     
    freightlinerman, Apr 6, 2014
    freightlinerman, Apr 6, 2014
    #1
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  3. Apr 6, 2014 #2
    bowtieboy77

    bowtieboy77 Light Load Member

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    Do not cut the belt or you will overheat! The fan hub is unlocked by air pressure controlled by a electric solenoid that controls the air flow to the fan. The fan stat gets its signal from the ecm which reads the engine temp. This is why you would hear a hiss with key on it had a air leak. If you cut the belt the crank wont drive the fan, fan wont spin, and you will overheat. Diagnose fan disconnect air line from hub and with key on check for air supply. If no air I would suspect faulty fan stat which will be located on firewall usually. Take shop air and put blower tip in to fan hub air port and check if fan dissingages. I have seen fan hubs fail and locking on. Also if it is a horton some models have 2 holes in the front that you can thread to 3/8 bolts into to lock it on. The bolts should not be there only for emergencies to get you to a shop. Mayby previous owner locked it with bolts.
     
    bowtieboy77, Apr 6, 2014
    bowtieboy77, Apr 6, 2014
    #2
  4. Apr 6, 2014 #3
    Yogibear

    Yogibear Light Load Member

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    Nov 4, 2008
    Bristol, Florida
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    You have to first identify the style fan clutch you have. Most take air to engage but you may have a Kysor for example that takes air to release. once you have identified the system you have it will be easier to trouble shoot than assuming you have air pressure locking up the fan.
     
    Yogibear, Apr 6, 2014
    Yogibear, Apr 6, 2014
    #3
  5. Apr 6, 2014 #4
    freightlinerman

    freightlinerman Road Train Member

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    Florida
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    I believe it is a kysor. When I start the truck with no air, it takes till about 65 PSI to disengage the fan hub, it stops running. When I turn the key on, or off, there is a brief hiss of it airing up. The A/C system is a Kysor. I see one tiny little air line the size of a spaghetti string that runs from the fan hub through the side of the block, then it branches into a valve near the engine that branches further down to the fire wall where there is a 2 wire sensor, which then connects to the main air connection.

    I don't pull anything with this truck, I just bob tail around with a pick up bed on the back. The fan has never came on and never gotten close to over heating. Before this happened, the fan would disengage after building up air pressure. Cutting the belt wouldn't bother me. I can idle all day at 1,000 RPM with no issue.
     
    freightlinerman, Apr 6, 2014
    freightlinerman, Apr 6, 2014
    #4
  7. Apr 6, 2014 #5
    spyder7723

    spyder7723 Road Train Member

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    sarasota, fl
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    Logic. Either you have the only detroit on the planet that doesn't need a fan, or maybe you should get it fixed instead of removing it. Which seems more likely?
     
    spyder7723, Apr 6, 2014
    spyder7723, Apr 6, 2014
    #5
  8. Apr 6, 2014 #6
    passingthru69

    passingthru69 Road Train Member

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    I would go with fixing the problem. My Detroit heats up even at an idle. Might be the selenoid went bad.
    Check for power at the selenoid
     
    passingthru69, Apr 6, 2014
    passingthru69, Apr 6, 2014
    #6
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