Engine fan on, coolant temp low.

Discussion in 'Ask An Owner Operator' started by BJSingh_TruckersReport, Oct 24, 2021.

  1. mtoo

    mtoo Road Train Member

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  3. BJSingh_TruckersReport

    BJSingh_TruckersReport Bobtail Member

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    I do have a switch on the dash for the fan, it’s in the AUTO position. The fan is on with or without A/C on.

    I see two pressure switches by the EVAP valve, both are labeled A/C HP Switch. I have another pressure switch on the SMALL Line coming out of the A/C Compressor, this one is labeled A/C Pressure Switch…which one controls the fan?
     
  4. mudflap77

    mudflap77 Heavy Load Member

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    Build up air, shut the engine off, turn the key to the on position (make sure the a/c is off and engine temp is low enough that the fan won't be locked), try to spin the fan by hand. If you can't turn it your fan clutch is worn out.
     
  5. BJSingh_TruckersReport

    BJSingh_TruckersReport Bobtail Member

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  6. mudflap77

    mudflap77 Heavy Load Member

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    You're welcome. Next step is connect cummins insite and see what is calling for the fan..
     
  7. BJSingh_TruckersReport

    BJSingh_TruckersReport Bobtail Member

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    Man, i was hoping to avoid the expense of a diag charge from Peterbilt.
     
  8. Gliding ProStar

    Gliding ProStar Medium Load Member

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    I wouldn't take it to Peterbilt. I would go to a local independent with a proper scan tool or Cummins Insite and ask them to diagnose it.
     
  9. Long FLD

    Long FLD Road Train Member

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    Wasn’t on a Cummins, but I had an intake air temp sensor go bad on a Cat and it caused the fan to run constant.
     
  10. Antinomian

    Antinomian Road Train Member

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    Try unplugging those AC high pressure sensors you found first and see if one of them makes the fan turn off. You may need to stop the engine and unplug it, then start it up. Worth a try, though I don't know if those are normally-closed or normally-open switches. The other thing that will make the fan come on is the coolant temperature sensor.
     
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