2010Prius- AC would occasionally stop blowing cold air (Issue in Servo? Evaporator? or Amplifier?)

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by priusth2010, Aug 26, 2021.

  1. priusth2010

    priusth2010 New Member

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    Hi All, first time posting and a bit of long post - Need help in sleuthing the AC issues in my car.

    7 years owner of a 3rd Gen 2010 Prius (150K km) - With the tropical climate temperature in where I live, I've always kept the AC running on full blast while my driving (Auto-Mode set to around 23'C to 25'C)

    In the past 3 months or so, every once in a while the AC in my car would stop blowing cold air.
    From what I observed, this would normally happen during a long drive with a lot of extended idling (e.g. 20 to 30 minute idling in a 40-50 minute drive).
    When it happened, it would start with a drop in the air breeze coming out of the vent and after a minute or two, the air coming out of the vent wouldn't even be cold at all (sort of like Fan-mode only)
    >>> The WEIRD thing is, the whole issue would go away once I turn off the car, wait for 15+ minute and turn it on again - the AC will be back to normal.

    I've brought my car to a local mechanic (a dedicated PRIUS shop) several times since this happened - the first time I brought it in, it was a day after I encountered the issue, hence the AC was working properly then, the owner/lead mechanic plugged in a TDT into the car and told me there's an error code - something to do with Servo (?) (I didnt remember to ask him for code number - but see note**note-1** below).
    He looked at the Servo (not sure which one - it's under the driver seat) - and told me things seem to be working ok (well yeah the AC is working fine then) - He simply reset the error code. He told me maybe the error code was just a false positive since if it is really the servo issue, the system will not even allow him to reset the code (is this true??).

    Few weeks after - the issue happened again, and this time I went straight to the mechanic shop without turning off the car (AC blowing warm air and all). This time he plugged in the TDT and no error code came up. His crew proceed to clean the front condensor and top up the freon (think he mention something about freon not being full?)

    Today (couple weeks after the second trip), the issue happened again - again I went straight to the shop (it's only 3 min away from my home) - this time, again no error code. He peeked under the dash to look at the servo (not sure what he's looking for). Then he ended up topping up the freon again (he mentioned it's okay). and he suspected that the Evaporator might be either dirty (need cleaning) or might be leaking (need replacement) (???)- this suggestion make me super skeptical.

    **note-1** 2 years back, I had the AC evaporator replaced; brought it in couple times to a Toyota dealer and was eventually told it's the leakage in the evaporator(they tested by filling in the freon first but after couple days the issue still persist)
    3 weeks after the evaporator was replaced back then, I bumped into this issue of cold air not blowing out (although it went away after car restart), went back to the dealer, and was told there's a error code: DTC B1441. The dealer just cleared the code since all seem to be fine. Since that point I've been starting my AC by pressing "Auto" (before I mostly use the fan up/down button) - and all seem to be OK till now.

    I dug deeper in the forum and found out DTC B1441 error has something to do with "Air Mix Servo" part - and from the description of the error in the repair manual this does sound to be issue that I'm experiencing. I did remember seeing the mechanic check the Servo and told me

    My questions:
    - How likely is it for a two-years old evaporator to be leaking again?
    - How do we know if servo is working properly or not? (I'm not a big auto-mechanic person)
    - The one million dollar question: What seems to be the issue? (Evaporator/Air Mix Servo/ AC Amplifier?)


    Other things of note:
    **note-2** Recently, (these past 2-3 weeks) I can smell faint odor from outside the car even when AC vent is set to recirculate (Servo inlet issue??)
    **note-3** Previously, I turned on my AC manually through the Fan Up/Down button and every now and then the air-flow would seeem to malfunction (setting would be in "Face" but air coming out from "Face-Foot" or "DEF" but coming out at "FACE - low vent"- this would go away when I restart the car after stopping for few minutes) - this seem to go away after I started turning on the AC via "Auto" button. (Servo outlet issue??)
    >> skimping through the repair manual - could all these caused by a faulty AC amplifier - maybe?


    **note-4** on the local mechanic shop; this is one of the few shops (maybe two) in my city that do work specifically on Prius - everytime I visit, I can see 10-20 Prius-es going in and out his garage. So I'm assuming (hoping?) the owner know what he's doing(he's so far been okay and pretty spot on with his other fixes albeit minor ones) - also he's been quite fair w/ his pricing; In the three recent visits that I had for this issue - he only charged me once (the 2nd one when they did the cleaning). Although his last diagnosis on the evaporator make me bit skeptical.
     
  2. rjparker

    rjparker Senior Member

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    First it does sound like there is a leak but they can't find it. The evaporator is always blamed in those cases but it typically takes a skilled ac specialist to find a difficult leak. Usually there are no codes for low refrigerant. Topping off is a waste of money if it leaks out quickly.

    Most likely you do have an airflow servo problem if the code is there and the air flow is misdirected. This just may make the air flow come out in an inefficient way like on the floor. Setting the fan speed manually will bypass the Auto mode which tends to slow the fan. An eco driving mode can shutoff the compressor as could an overheating engine. These are obvious so they may be unlikely.

    This ac tech has many videos on Prius ac and sometimes checks this forum:
     
    #2 rjparker, Aug 26, 2021
    Last edited: Aug 26, 2021
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  3. ChapmanF

    ChapmanF Senior Member

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    There are three different servos in the HVAC box. What happens if one isn't working depends on which one.

    If the air inlet servo doesn't work, you'll be getting fresh air when you want recirculated, or vice versa.

    If the air outlet servo doesn't work, you'll get air coming out where you didn't want, like the floor.

    If the air mix servo doesn't work, you'll get hot air when you want cool, or vice versa.

    B1441 refers to the air mix servo.

    In the Repair Manual section for B1441, there is a "Hint: confirm that no mechanical problem is present ..." before just concluding the problem is really the servo itself. There's another recent thread (just this week IIRC) where somebody was getting the code, but saw the servo itself seeming to move the right way ... but inside the HVAC box it mechanically wasn't moving the air max door really.
     
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  4. priusth2010

    priusth2010 New Member

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    Thanks for the reply - main reason why I am skeptical with the mechanic's suggestion on a leaking evaporator as the source of issue is because I've just recently replaced the evaporator (about 2 years ago - due to confirmed leakage - work done by dealer & parts from denso). How fragile is the evaporator part anyway?

    also as in my note above - I did bump into a similar issue (DTC B1441) couple weeks after the initial evaporator replacement work was done 2 years back (dealer reset the code & which I've started to just turn-on the AC via pushing the "Auto" button - these seem to do the trick till now)

    I'm guessing one of the servo might be problematic?


    Sorry but what do you mean by "slowing the fan"
     
    #4 priusth2010, Aug 27, 2021
    Last edited: Aug 27, 2021
  5. ChapmanF

    ChapmanF Senior Member

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  6. priusth2010

    priusth2010 New Member

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    Thanks for the response - yes from what I read and saw in the repair manual - am aware of the three different servos in the HVAC system ..

    quick question:
    I'm no mechanic and never actually seen the any of the three servos directly but how do I verify that the air-mix servo is not moving the air-mix door? (tbh I don't even know which one is the air-mix door)
     
  7. priusth2010

    priusth2010 New Member

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    Also would want to point out that this thing only came up every now and then (mostly during a drive with a prolonged idling - 20-40 minutes idling?).

    and in all the times that it happenned, turning off the car completely and restarting it after 15+ minutes would solve the issues.
     
  8. ChapmanF

    ChapmanF Senior Member

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    You might have to begin by changing the "never directly seen" part. While they are difficult to reach, you ought to be able to get a view of the servos by removing the glove box. Then put the air mix through its paces by having your accomplice change the heater's temperature setting from LO to HI (or use the test mode described in the repair manual) while you watch the servo.

    Then what you hope for is that you actually don't see the servo working as you expect, and you have a simple problem that can be fixed with the servo or its wiring. I almost wish I hadn't mentioned the other guy's servo moving with the door linkage failing internally; clearly that can happen, which was the point of mentioning it, but it's a coin-lands-on-edge case, and it isn't the case you want, because that's a PITA to fix.

    The deduction that the door isn't moving is easy, if you see the servo moving and the engine is running at operating temp but the air temperature doesn't change. One thing that took extra time in the other guy's thread was that he didn't at first believe his symptoms could be explained that way, so he couldn't get there until he saw it with his own eyes.
     
  9. rjparker

    rjparker Senior Member

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    While not directly a problem for the ac, long periods of Ready while not moving, eg "idling", is not good for your engine or the hv battery. Advice from a trusted Toyota master mechanic and my own experience. For one thing the engine experiences pretty significant thermal cycling particularly in hot weather with the ac on. As much as 50f many times in 40 minutes. Possible head gasket ramifications as well. The hv battery is allowed to discharge and then slightly charges but only a little.

    Certainly a refrigerant leak is the most common failure mode, apparently techs have topped of your refrigerant a couple of times. Likely without repairing what could be a big leak. Plus you have observed a servo blend door failure which is still there as well. I don't think there will be a simple fix either way.

    Like everything, logical diagnosis starts by knowing how the system normally works. Ideally at a functional and a technical level. It then becomes easier to determine where failures exists. Much of that skill is learned from experience but depends on fundamental knowledge and accurate documentation.

    The fan slowing in Auto is exactly that, the automatic control in Auto will slow the fan speed. A lot. Using the manual fan speed control locks the fan speed in.

    The servos acting up is a problem that needs repair just like a repeated low refrigerant level means you have a leak. It theoretically could be the controls causing random servo movements but the odds are it is the observable mode failure. Careful observation should isolate which servo / blend door / air flow mode is consistently failing. Certainly if the heat blend door is allowing hot coolant to warm your cooled air the ac would be ok when the engine coolant is cold. But the coolant builds heat within five minutes and stays somewhere between 150f-205f under most conditions. So if you can get cold air anytime (around 40f at the vent in recirc if everything is good) when the engine is warm, the odds of a stuck mix door is slim. Certainly if you can adjust the temp from 70f to 85f and it goes from cold to hot quickly, you are testing the blend door.
     
    #9 rjparker, Aug 28, 2021
    Last edited: Aug 28, 2021
  10. ChapmanF

    ChapmanF Senior Member

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    I think that was part of the misconception in Pyro da Cat's thread that led to a delay in solving the problem there. It's important not to forget that the hot coolant is only circulating in the heater when the water pump runs, and that pump is electric and under ECM control.

    When you have set the controls for heat, the ECM keeps the water pump running even when the engine stops, and the air keeps blowing warm a long time, on the heat in the coolant itself and in the mass of engine metal.

    But when you don't have the controls set for heat, the ECM stops the pump whenever the engine stops. The air quickly finishes off the heat of the ounces of coolant stopped in the heater core, and then blows cool, even though the indicated temperature of the (non-circulating) coolant is still pretty hot. As soon as the engine restarts, the pump restarts also, and bang, the air is warm again, without much delay.

    Overlooking that involvement of the water pump seemed to be why Pyro at first assumed the odds of a stuck mix door were slim, and had to sort of put his finger into the mark of the nails before believing.
     
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