Cooling fan #1 not working when AC is on. 2011 Prius

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by George Jung, May 29, 2024.

  1. George Jung

    George Jung New Member

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    Vehicle:
    2011 Prius
    Model:
    IV
    The fan on passenger side doesn't work when i have the AC on but when i turn climate control off it runs when it gets over about ~205 degrees F. I believe that would be cooling fan #1. Is that the AC condenser fan? When i am driving the AC blows cold but when i am stopped it blows warm air. I have watched the engine temp on my phone and it has reached as high as 230* one time when i was at a really long stoplight for multiple light cycles in 100* heat.

    I tested relays R2 (cooling fan No 3) R4 (cooling fan No 1) and R8 Cooling fan #2) for continuance on multimeter and they all beeped and clicked when i attached alligator clips from the 12v.

    It sounds like from reading other threads it may be the AC pressure sensor or the engine temperature sensor. How can i further test this to see what the issue is? I've downloaded the wiring diagram and its honestly just confused me.
     
    #1 George Jung, May 29, 2024
  2. BiomedO1

    BiomedO1 Senior Member

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    If the AC condenser, in front of the radiator, runs the entire length of the radiator - both fans should be turning when the AC is ON.
    Some early Hondas had an AC condenser on one half and a radiator on the other half (NO stacking of cooling coils) - in that case the fans would operate separately. I haven't been under the hood of a gen3, so not sure how it's setup.
    Usually when one fan is dead, the fan motor is dead. You can disconnect the fan motor wire and jump directly to a battery to see if it's working.

    Hope this helps...
    FYI. fans should turn-on when coolant is around 200F - both of them, if they run the length of the radiator.
     
    #2 BiomedO1, May 30, 2024
    Last edited: May 30, 2024
  3. George Jung

    George Jung New Member

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    I think im just going to tap a fuse and wire in a new wire since i cant figure it out. I read the service manual but all it says to do is replace wiring harness so i dont know how to proceed. Is there a way to tap a relay or something so fan #2 will turn on when fan #1 turns on?
     
    #3 George Jung, May 30, 2024
  4. BiomedO1

    BiomedO1 Senior Member

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    Have you determined that both fans are working properly?
    Do they run when 12VDC is applied to them directly?
    Did the two motor windings ohm out close to each other?
    Has an animal been chewing on your harness or any other visible damage?

    IMHO; if wiring diagrams confuse you - you probably shouldn't be rewiring your car. You may end up frying a very expensive component; like an ECU. Some car cooling fans are regulated, turns faster when hotter - so not a simple on-off. Patching a wire across would definitely mess up a system like that- since you just doubled the resistance on that circuit. Take it to a professional, since it seems to be beyond your ability.
     
    #4 BiomedO1, May 31, 2024
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