Force ICE to start before SOC bars purple when A/C on?

Discussion in 'Gen 2 Prius Technical Discussion' started by pasadena_commut, Jul 5, 2025 at 8:20 PM.

  1. pasadena_commut

    pasadena_commut Senior Member

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    Lately I have had to make a lot of short trips in hot weather with lots of stop and go, and it feels like mostly stop. The A/C is on, the car doesn't get much of a chance to charge when driven like that so the SOC stays in the lower part of its range, and at stops SOC has dropped into the purple bars, often without starting the ICE before the light changes. So when the light changes and the ICE starts the car wants to charge the battery heavily, and then the car doesn't accelerate well.

    It would be better, from my perspective, if I could force the ICE to start sooner, like at one blue bar, when the car has been or will be sitting for a long time. When this is needed the transmission is in D and my right foot is on the brake. I suppose I could put it in P and press the gas, which would start the ICE. Is there a way to do it without shifting out of D or taking my right foot off the brake?

    Sometimes I turn off the A/C to prevent the SOC from dropping into purple. Not a good workaround though because the car heats up very quickly in the sun when the A/C isn't on. Also I worry that it might not be great for the A/C to be turned on and off like that.

    Note: temps in the high 80's or low 90's, although the "outside temp" display is often over 100. That only comes down to something approximating the true temperature with extended driving. This is what comes of putting the air intake next to a lot of hot metal and glass.
     
    #1 pasadena_commut, Jul 5, 2025 at 8:20 PM
  2. dolj

    dolj Senior Member

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    You can force-charge it in D; there is no need to move to P.
     
    #2 dolj, Jul 5, 2025 at 8:45 PM
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  3. Tombukt2

    Tombukt2 Senior Member

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    Putting in p will start the ice but I don't notice it charging the car like when I put it in D and hold the brake which is easier for me to do in traffic than for whatever reason I would be moving it to p or N for I think it do not charge them ? I have to be in seriously heavy traffic which I avoid like plague or really driving like I'm lost which is rare. I also do not fit parked w airs on I get the hair out of my car onto someone's free air McDonald's the silly strip mall etc . Prius do not do mobile office worthy at all
     
    #3 Tombukt2, Jul 6, 2025 at 7:39 AM
  4. Isaac Zachary

    Isaac Zachary Senior Member

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    May I ask what your goal is? Why do you think it would be better, from your perspective, if the gasoline engine turned on and started charging the battery before the battery bars got down to the purple ones?

    Remember that the battery isn't really down near 0%, but from no bars to full bars is only something like 30% to 70% state-of-charge, so it's not like it's hurting the battery from deep discharging it.

    It does hurt fuel economy. But then again, using the A/C while driving around in stop-and-go traffic in any car will hurt fuel economy.
     
    #4 Isaac Zachary, Jul 6, 2025 at 9:08 AM
  5. Brian1954

    Brian1954 Senior Member

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    The correct values are 40% to 80% state of charge.
     
    #5 Brian1954, Jul 6, 2025 at 9:27 AM
    Last edited: Jul 6, 2025 at 10:01 AM
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  6. pasadena_commut

    pasadena_commut Senior Member

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    Primarily it is to be able to drive the car normally at all times that it is moving. When it is down in the purple bars the car struggles to keep up with traffic. If there was nobody around I would just live with the slow acceleration, what do I care if it takes an extra 20 seconds to get up to speed? Unfortunately the people behind me in these situations don't have the same patience.
     
    #6 pasadena_commut, Jul 6, 2025 at 1:37 PM
  7. Tombukt2

    Tombukt2 Senior Member

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    And this is going on in sunny Southern California where it never rains and beautiful weather. Wow. But in a business suit I guess. Can be pretty hot
     
    #7 Tombukt2, Jul 6, 2025 at 2:32 PM
  8. Tombukt2

    Tombukt2 Senior Member

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    And you guys have lots of traffic right big California like Texas but lots standing traffic. Yeah I couldn't do that at all . My brothers in thousand oaks Ive not been to visit. I'm fraid I'll spend all my time in traffic.
     
    #8 Tombukt2, Jul 6, 2025 at 2:34 PM
  9. Tombukt2

    Tombukt2 Senior Member

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    I noticed that if I have the fan above medium for some reason it pulls the HV display down quicker . Alot . I usually run med or 1 sq below it . With proper system on 102 degree day just the other day . Quite cold in car and staying in blue in town . And if I'm sitting in traffic on the highway I can just floor it and hold brake . I catch this early on hi way stops.
     
    #9 Tombukt2, Jul 6, 2025 at 2:46 PM
  10. ChapmanF

    ChapmanF Senior Member

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    The fan runs off the 12-volt system. But the higher the fan runs, the faster heat gets transferred to the evaporator, so the compressor can run harder to dispose of it, and the compressor runs off the high-voltage system. If you watch the "A/C watts" reading (power consumed by the compressor) on a scan tool, you can see that effect.

    I know there's an A/C watts PID in gen 3, anyway. I might not have seen it in gen 2 but I would expect it to be there, since the compressor was already electric in gen 2.
     
    #10 ChapmanF, Jul 6, 2025 at 3:03 PM
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