A/C and Heater Fan Failure Under Low Air Flow Conditions

Discussion in 'Gen 2 Prius Technical Discussion' started by John Kristl, Oct 16, 2019.

  1. John Kristl

    John Kristl Junior Member

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    Location:
    Boulder, CO
    Vehicle:
    2007 Prius
    Model:
    Two
    2007 Prius, 229,000 miles: When running in warmer temps over approximately 84 degrees in stop and go traffic the A/C suddenly quits and just blows hot air. If I get going faster after a mile or so the air gets cold again. If sitting still with the engine running and heater on for awhile, 60 degrees or less, then I shut the car off to go into a store and come back out...no heater fan. It will not blow at all. If I leave the car running the fan still runs.

    In both circumstances I can lift the hood and let it cool for 5-10 minutes and everything will work just fine.

    I took it to a very knowledgeable Prius mechanic and he replaced the inverter pump. That didn't help any so he replaced the inverter with a used, believed to be a good one. Didn't help. I replaced the radiator fans. Didn't help.

    I have noticed that the fans will run really fast once in awhile like at a stop light but do not run fast under the problem conditions. They are running but just low speed.

    The mechanic wants to replace the radiator to see if that does it but I am holding off on more expense until I get more feedback.

    Radiator fan controls? What controls that? Any other ideas?
     
    #1 John Kristl, Oct 16, 2019
    Last edited: Oct 16, 2019
  2. lech auto air conditionin

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    Vehicle:
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    Model:
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    I could tell you one thing I am 100% sure of. You did not take it to a knowledgeable Prius mechanic. This is a diagnosis I could stand behind.
    This is always like diagnosing over the telephone when you think there’s some information that is missing that could lead you down the wrong road or recommendation.
    Trying to read between your sentences between the
    #1 cooling problem and the
    #2heater problem
    #3 interior blower Dash fan sometimes works and sometimes does not.
    #4 When the interior fan does work on a hot day the air conditioning is working fine when you’re driving down the road but when you come to stop and go traffic when you’re standing still ?.
    A: The air conditioning cooling turns off but the blower fan keeps running and you start feeling hot air?.
    Questions
    1: has the air-conditioning recently been recharged within the last year?
    2: has the vehicle been in a front end collision where the bumper or hood or radiator support had to be repaired recently
    3: has there been any under the hood service procedures performed for maintenance recently.

    4: before having more parts shotgun repair style find a shop that specializes in Prius only and have been in business for more than 5 to 10 years at least.
    The next best thing find a shop that specializes in Toyotas. stay away from the shops that specialize in everything Ford Chevy Chrysler Honda Mitsubishi Suzuki infinity Lexus

    as for your heater problem there’s a lot of good mines on this form with a lot of experience combined between everyone here your problem may get solved.
     
  3. lech auto air conditionin

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    I forgot to add one thing have your 12 V battery checked just in case funny things happen when they start to get weak.
     
  4. John Kristl

    John Kristl Junior Member

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    Location:
    Boulder, CO
    Vehicle:
    2007 Prius
    Model:
    Two
    I took it to Boulder Hybrids, a Prius specialist that has been in business for years. He first replaced the inverter cooling pump, and when that did not help he replaced the inverter with another used one and that did not help. He says that the next step is to replace the radiator with a known good one and see if that helps. Then check the temperature of the transaxle and see if that is overheating. Since we are into cold weather these cannot be done.

    Now, in colder weather, the heater fan is acting up, seemingly caused by an overheating inverter. I can make it work again by sitting with the hood up for 10 minutes to cool the inverter.

    Blower for heat and A/C not working both seem to be related to the inverter being too hot.

    Under these "too hot inverter" conditions the radiator fans are not running on high, roaring like they should. So I am thinking that there is a control somewhere that is not turning them on to high. Boulder Hybrids does not know what controls them.

    The A/C works fine on cold days. It will blow cold.

    There has not been any recharge or any work on the A/C or any other work under the hood except replacing the headlights a long time ago. And there has not been any damage. The car has been just fine until this issue.
     
  5. lech auto air conditionin

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    Wow. Then n that case it sounds like, I feel sorry for the technician who has to diagnosis this car.
    1: This car has never been in a flood ?.
    2: Had a selvage title
    3: Technician used Techstream on a test drive for confrontation of transaxle overheating?.

    if all these things started happening at the same time Intermittently Did the technician start looking for bad grounds. Voltage problems.

    Give the car to the technician to used to drive home using Techstream for a few days.

    sounds like you need to catch the eye of someone here on PriusChat may have had exactly the same symptoms and solved it.

    Since this is a hybrid specialist and I don’t remember reading that the 12V battery was tested ?. Or replaced ?.

    I can’t wait to find out what finally fix’s this problem.

    Since this is a hybrid Spectly shop he must be slammed with work no time to spare and by now this car is eating up his time.
     
  6. dolj

    dolj Senior Member

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    I find it hard to believe that a Prius Specialty shop does not know how the fans work. They're run by two relays that can run them in serial for one speed and in parallel for the other speed. It is all in the electrical wiring diagram. Tell him to go look on Toyota's Technical Information System website.
     
  7. lech auto air conditionin

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    Do you get the same impression that I get a lot of shotgunning of replacement of components is happening instead of diagnosing
     
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  8. dolj

    dolj Senior Member

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    Yup.
     
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