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Impossible to have climate control set to ONLY not exceed a temperature, right?

Discussion in 'Gen 3 Prius Main Forum' started by Johnny Cakes, Jul 15, 2021.

  1. Johnny Cakes

    Johnny Cakes Senior Member

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    Obviously, you can set the climate control to (for example) 70 and it will keep the cabin at 70.

    Is it possible to set the climate control to not exceed 70? So no matter how cold it gets, that's AOK, but should the temp exceed 70 then the climate control cools the air?

    House thermostats have that function, it doesn't seem like if its possible in the Prius,
     
  2. PriusCamper

    PriusCamper Senior Member

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    That would make too much sense... Life is all about being too hot or too cold, not just right. Goldilocks and the three bears is fake news!
     
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  3. rjparker

    rjparker Tu Humilde Sirviente

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    Thats Auto mode
     
  4. Johnny Cakes

    Johnny Cakes Senior Member

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    @rjparker Auto mode keeps the temperature at 70. I'd like it to only cool *above* 70 and totally ignore any temperature under 70. Like when the home thermostat is set to "cool." It has no ability to heat.

    @PriusCamper As a fellow camper, you know what I'm talking about. It's pretty easy to have a warm sleeping bag or blanket that's going to serve just fine throughout the night. Low temps are not a problem. But once that Florida sun starts to hit the car in the morning, it's oven time. I've become accustom to the "shake" when the ICE starts and normally sleep right through it, but it can be jarring in a light sleep so not having the battery used to heat the car under 70 would be awesome. Also, the less the ICE runs the better for stealth camping.
     
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  5. PriusCamper

    PriusCamper Senior Member

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    Yeah, I've camped in my Prius many times even at temps as low as 15 degrees fahrenheit but I've never left the car on overnight. Instead I wake up and turn the car and heater on for 15 minutes. And when in a hot place that heats up first thing in the morning, that's my alarm clock to wake up and start driving more. :)
     
  6. rjparker

    rjparker Tu Humilde Sirviente

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    Turn it off auto and press ac
     
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  7. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    I can't think of a way to do this with the controls provided.

    The easiest hack I can think of would be to spoof the interior temp sensor. Assuming it's some kind of thermistor, add a cut-out switch and put a fixed value resistance equivalent to 70°F on that line so that the car thinks there's no HVAC work to do.

    Once the sun hits the sensor on the dash, it'll add some cooling and that might get you to when you'd wake up normally. Then you would throw the switch to go back to full auto.
     
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  8. dbstoo

    dbstoo Senior Member

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    That should do it. So simple.
     
  9. jerrymildred

    jerrymildred Senior Member

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    That's what I'd try doing. If it's in AC with the temp set to 70 and NOT in auto, I would expect it to not run in heat mode. But that's impossible for me to test in this location at this time of year since our morning lows are usually about 80º and it refuses to go under 75º.
     
  10. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Maybe ours is different, but if I did that in our car, the air conditioner would run continuously at the set level, rather than only when needed as controlled by the thermostat.

    This would certainly allow the car to get quite cool overnight, but it would use more energy and run the engine more.

    I think the real goal is "run the engine as little as possible" and not "prevent the heater from running"
     
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  11. rjparker

    rjparker Tu Humilde Sirviente

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    The thermostat works with auto on or off. Realize that the air coming out of the vents will usually be significantly cooler until it mixes. The car also factors in solar radiation during the day.
     
  12. Johnny Cakes

    Johnny Cakes Senior Member

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    Bingo! ....and prevent the car from getting hot. No concern about the car getting too cold.
     
  13. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Then it's worthy of an experiment to see if that runs the engine "less enough."
     
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  14. jerrymildred

    jerrymildred Senior Member

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    Agreed! We can kick around ideas all day, but you don't know for sure till you try it. Our low this morning was 81 and it's 86 in the garage, so not much chance of experimentation here. :unsure:
     
  15. Johnny Cakes

    Johnny Cakes Senior Member

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    Not getting cold in these parts either, not even at night, so you are right, can't test.

    But as I was cruising today, I was thinking that this solution might a flaw: once the climate control is not in AUTO, it can't control the fan. So the fan would always be blowing at whatever level was manually set. And if the sun really starts to beat down, that level might be too low to cool the car. At night when its cold, that level might be too high, wasting the battery and causing the ICE to run (which I'm trying to avoid).
     
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  16. PriusCamper

    PriusCamper Senior Member

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    Another reason to develop your skills and tricks for manually controlling the weather inside your Prius so well you can do it in your sleep. :)
     
  17. Leadfoot J. McCoalroller

    Leadfoot J. McCoalroller Senior Member

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    Well that's exactly what needs to be tested. I was thinking about it too- my old Subaru would pass this test. It had full auto climate control, but if you hit the mode button then the mode is the only component that would not be automatic. Likewise if you had been in auto and pressed the fan speed + button, then the fan speed would go up one notch and stay there forever, but the mode would still be automatic.

    In other words there is such a thing as semi-automatic on that car, and there's no reason that a Prius system couldn't work the same way.
     
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  18. Johnny Cakes

    Johnny Cakes Senior Member

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    Tested this today -- works with the Prius!
     
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