Fan doesn't come on with AC

Discussion in 'Kenworth Forum' started by irishluck09, Jun 14, 2022.

  1. irishluck09

    irishluck09 Light Load Member

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    1998 kw w900 n14

    So recently we got my fan clutch working and my AC.

    Problem now is my AC works but the fan doesn't come on when it's needed so I have to run the fan manually as not to damage my compressor. We've checked everything. Installed a new fan switch and nothing. At this piont we think there is a broken wire.

    Can I run a new jumper wire? Like from the fan override sensor to the compressor? Or where ever it goes? Does anyone know where a can run a jumper wire?
     
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  3. spsauerland

    spsauerland Road Train Member

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    So if you look at the diagram I attached in your other thread, the A/C high pressure switch is an input to the ECM. It is called a Unitary Switch on diagram, has A5 next to it. Wires going to it are gray (common from ECM) and green/white (signal to ECM). Signal goes to connector A of ECM, pin #8. If circuit is intact, just unplugging the pressure switch should make the fan come on.
     
  4. irishluck09

    irishluck09 Light Load Member

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    Okay so it is #8. That was my big question cause I wasn't actually sure if that was it. So my problem is likely between pin #8 and the high pressure switch, correct? Cause I can ohm that out and see if it has a broken wire in there
     
  5. spsauerland

    spsauerland Road Train Member

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    Not necessarily. If you look at the diagram, the switch is a Normally closed switch. When refrigerant pressure on high side increases, the switch opens and circuit is opened letting ECM know to turn on fan. If wire was open the fan should run all the time. You really need Insite or a quality scan tool so you can see the status of the a/c high pressure switch that ECM sees and go from there.
     
  6. irishluck09

    irishluck09 Light Load Member

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    I think my mechanics have insite. Ill have to ask them. And that switch your talking about is the one called "unitary sw" on the diagram correct? that is the high pressure sensor/switch?

    When we got the AC fixed we did try a brand new High pressure sensor and also put on a brand new plug as well.
     
  7. spsauerland

    spsauerland Road Train Member

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    Yep, the Unitary Switch. Insite will really help narrow the issue down.
     
  8. Mr.kenwortht800

    Mr.kenwortht800 Bobtail Member

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    Jun 24, 2022
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    I want to charge the ac on my 04 Ken t800, can’t find the low side port. Can someone point me in the right direction.
     
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