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2005 Peterbilt 378, Intermittent Fan

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Mountain_Dweller, Sep 27, 2018.

  1. Sep 27, 2018 #1
    Mountain_Dweller

    Mountain_Dweller Bobtail Member

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    Oct 18, 2014
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    Good evening!

    I have a 2005 Pete 378 with a C15, MXS serial. The fan is on nearly all the time, and it intermittently cuts out when it’s supposed to be off but is otherwise on. Sometimes it does this rapid fire. Just put a new clutch on it because it went bad probably from this issue. I imagine the root cause is a bad wire or connection.

    So I’ve been poking around and was under the impression that the dash switch was the last step in the chain before the solenoid, but am not positive about that. Is there a diagram of this circuit out there somewhere or can someone explain what goes through the ECM and how the power gets from there to the solenoid? Otherwise I’m just guessing!

    Thanks!!!

    - Nathan
     
    Mountain_Dweller, Sep 27, 2018
    Mountain_Dweller, Sep 27, 2018
    #1
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  3. Sep 27, 2018 #2
    Goodysnap

    Goodysnap Road Train Member

    3,752
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    Jul 12, 2017
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    Start with fan cycle switch on the high side ac line. Repin and replace the connector too. Cut back the wires to new good copper. The switches fail and pins and connector get loose and lose contact. If the circuit goes open and the fan will come on, the ecm timer starts all over again. You can also fit a jumper temporarily to see if that's the issue.

    This is the first most likely issue. A close second would be fan solenoid or wiring.
     
    Goodysnap, Sep 27, 2018
    Goodysnap, Sep 27, 2018
    #2
    peterbilt_2005, Mountain_Dweller and spsauerland Thank this.
  4. Sep 28, 2018 #4
    Mountain_Dweller

    Mountain_Dweller Bobtail Member

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    Oct 18, 2014
    0
    Morning. Thanks for the help! I’ll give that a shot. I should have mentioned I swapped the solenoid too.

    The high pressure switch is the one up near the radiator and compressor right?

    I am quite sure the fan is cutting on and off much faster than the ECM would allow, is there anything that actually bypasses it to bring the fan on?

    Best,

    Nathan
     
    Mountain_Dweller, Sep 28, 2018
    Mountain_Dweller, Sep 28, 2018
    #4
    Goodysnap Thanks this.
  5. Sep 28, 2018 #4
    Mountain_Dweller

    Mountain_Dweller Bobtail Member

    29
    12
    Oct 18, 2014
    0
    I should have asked, does the dash fan On/Auto switch go to the ECM to trigger the timer or does it just interrupt the ECM output pin going to the solenoid?

    -Nathan
     
    Mountain_Dweller, Sep 28, 2018
    Mountain_Dweller, Sep 28, 2018
    #4
  7. Sep 28, 2018 #5
    Goodysnap

    Goodysnap Road Train Member

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    Jul 12, 2017
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    Yes the ecm controls the fan. The switch is the one on the rad and is normally closed switch. Unplugged or switch open the fan will come on for the programmed timer amount until it sees closed again but must remain closed for fan to stay off. This is why an intermittent open will keep the fan running near constant depending on the timer length. Longer fan on time is encouraged to prevent rapid cycling of the fan clutch to lengthen fan clutch and belt life.

    Think of the override switch just as another ecm input to turn the fan on. No matter the input request for the fan the timer length is the same. The fan will only operate based the inputs received. Clear as mud????
     
    Goodysnap, Sep 28, 2018
    Goodysnap, Sep 28, 2018
    #5
  8. Feb 24, 2021 #7
    Tippytruck

    Tippytruck Bobtail Member

    1
    0
    Feb 24, 2021
    0
    Can anyone help me out. I have a 98 pete 378 that we are basically retrofitting with a c15 acert. I am having trouble finding the right fan clutch for it. Anyone have any ideas of a part number I could look for that would fit this application?
     
    Tippytruck, Feb 24, 2021
    Tippytruck, Feb 24, 2021
    #7
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