Bugs? (A/C and auto-high beams)

Discussion in 'Gen 5 Prius Main Forum' started by RogerPriusTX, Mar 4, 2025.

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  1. RogerPriusTX

    RogerPriusTX Junior Member

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    I understand that you are saying that having the A/C light on doesn't necessarily mean the compressor is running.

    However, in my quest for best mileage, when the temperature is nice outside (generally spring and fall), I just want to vent outside air into the car, and I don't want the car to think it needs to run the compressor (or the engine - more on that later). So, I set everything manually: set the fan by hand, turn the temperature down, turn off the A/C, and set the air source to be outside air.

    Regarding heating: the early Prius models (I've had a 2001, a 2007, a 2010, a 2018, and a 2024) generated heat by running the engine; setting the temperature to "LO" stopped this from happening. I understand that the Prius Prime has an electric heater -- possibly a heat pump? and that maybe newer versions all have a heat pump so that the engine doesn't have to run to heat the car.
     
    #61 RogerPriusTX, Mar 13, 2025
  2. RogerPriusTX

    RogerPriusTX Junior Member

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    I discovered (almost by accident) that if I turn on Auto, turn off A/C and set the can to heat in the winter, that the Auto will leave the fan off until warm air is available, and this is how I prefer to heat the car... let Auto control when there air goes and how strong it blows. It's worked well.


    It was still this way in the G5 today... I set Auto mode and then toggled the A/C on and then off... the Auto stayed lit.


    Very interesting information. Thank you!
     
    #62 RogerPriusTX, Mar 13, 2025
  3. RogerPriusTX

    RogerPriusTX Junior Member

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    I think I put the G4 on Auto at about the outside air temperature, and then toggled the air source and then ramped the temperature all the way down, and the fan speed never changed. (but now I'm doubting myself. I may try again).


    But the G5 doesn't. Of the A/C switch, the air source switches, and the fan speed, the Auto light only went out when I changed the fan speed - it stayed on no matter what I toggled A/C to, and no matter where I had the air source.
     
    #63 RogerPriusTX, Mar 13, 2025
  4. RogerPriusTX

    RogerPriusTX Junior Member

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    By the way, this topic has been a fascinating discussion; I appreciate the input of everyone.
     
    #64 RogerPriusTX, Mar 13, 2025
  5. Hammersmith

    Hammersmith Senior Member

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    No, that's not what it does.

    When it's set to on, Auto has control of the A/C by default. So Auto will turn the A/C compressor* on and off as needed to maintain the desired temp. The A/C light will stay off during this process as long as Auto is still selected.

    When this setting is set to off, Auto no longer has automatic control of the A/C. The driver decides when to enable A/C by using the A/C button. When the A/C light is off, so is the A/C. When the light is on, the system is allowed to run the A/C compressor as needed. This appears to be exactly what you've been asking for. (and what I tried to tell you to do in the second post in the thread)


    So change the setting to off, make sure the A/C light is off, then just hit the vent button when you want to bring in outside air. The A/C will stay off until you press the button to turn it back on. Pressing Auto will not reenable it. The system will now behave exactly like previous Prius generations.




    *or heat pump compressor in the Prime for those that want to be technical
     
    #65 Hammersmith, Mar 13, 2025
  6. ChapmanF

    ChapmanF Senior Member

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    In my gen 3, there are still some cases where the compressor will run without the A/C light showing. They are when defog modes are selected (either the full-blast defog button, or the feet-plus-windshield outlet mode).

    I don't have a gen 5, but I would not be surprised if the heat-pump compressor in a Prime can come on, for heating purposes, without lighting the A/C light. I suspect Toyota might prefer doing that over trying to explain to customers why now A/C also means heat.
     
    #66 ChapmanF, Mar 13, 2025
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  7. Hammersmith

    Hammersmith Senior Member

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    Certainly, but I didn't want to cloud the matter any more than I already was. Plus I'm getting a touch annoyed by people asking questions, me giving the correct answer, then those people not reading or trying the answer and continuing to complain/struggle for months/pages. It feels like it's happening more and more. It was probably Paul that pushed me into being annoyed initially, but now it's become like nails on a chalkboard. It's not a healthy mindset, but I'm having trouble shaking it.
     
    #67 Hammersmith, Mar 13, 2025
  8. RogerPriusTX

    RogerPriusTX Junior Member

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    Okay; perhaps I'll try this. This implies that pressing Auto should no longer do anything to the A/C light? If it's on, it should stay on, and if it's off, it should stay off.

    Having said that, most of the time (90% or more), I want Auto to control the A/C.

    What I had a problem with in the G5 was when that the auto light went off, the A/C stayed running, but the A/C light was off... and, in fact, with Auto "on", I could turn the A/C on and off without the Auto light going off. It makes it hard to know what state the car is in without pressing several buttons, which seems like a bad design.

    It may be that I would be happier with that setting OFF and just manually turn on the A/C when in Auto mode. Truth be told, when it gets warm here, I'll just leave it in the same state all the time.
     
    #68 RogerPriusTX, Mar 13, 2025
  9. RogerPriusTX

    RogerPriusTX Junior Member

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    I learned something I didn't know before about the G4, when I put the G4 climate control in Auto and bring up the Climate display, there is an "AUTO" label that shows up by the fan and be the vent settings. Changing either of these two turns off the Auto light, but leaves the "AUTO" label by the other one.

    I can change the air source (recirculate or not) and the A/C button on or off, and this does not change either label or the Auto light by the fan and vent settings.
     
    #69 RogerPriusTX, Mar 15, 2025
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  10. vvillovv

    vvillovv Senior Member

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    This is only where I wanted to make my first comment about the possible differences between the Gen 4 Prius and the Gen 4 Prime. Than a post or two later mentioning the Gen 4 heat pump ( a whole other issue of what it does and how best to use it ) . I never do use the heat pump for cabin heat, personally - - - at least not using any HAVC manual settings.

    This stuff isn't second nature to most of us. We see what happens while we are supposed to be driving and paying attention to the road. It's not often when we have many of the distractions of driving reduced to the point where we can evaluate observations easily. Thus it takes a long time (relatively) to start to understand
    what the car is doing on it own and what or if we are changing any of those base programming parameters by changing a setting or two on out screens.
    I'm still not sure there is a way to get the - old classic vent - mode in a Prius or Prime. Maybe possible, depending on how much of the HAVC system is being monitored for changes that may or may not effect MPG.
     
    #70 vvillovv, Mar 17, 2025
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