Climate Temp Setting Seemed to Reduce Fuel Economy with Auto Turned Off

Discussion in 'Gen 2 Prius Fuel Economy' started by cycledrum, Jul 10, 2009.

  1. cycledrum

    cycledrum PSOCSOASP

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    ** I don't think it is ever wise to dial a high temperature (i.e. 80F) into temp setting for Auto A/C mode. Who would want cabin 80F anyway? See below why**

    This morning, when 59F outside, I noticed warm air coming through upper vents into the cabin (I had outside air, upper vent selected, Auto/AC turned off). I did not expect warm air to come into the cabin since the auto system and fan were turned off (Didn't notice for a while since floor vents selected recently).

    Couple weeks prior, dialed the auto temp to 80F per someone's recommendation to make A/C work less on a hot day.

    But this backfired this morning as warm air coming into cabin on a cool morning, even with auto system turned off and outside air selected. Seems outside cool air should have come in, instead of heated air from engine which seemed to have reduced fuel economy on this tankload (only 50.5 MPG's. should be couple MPG's higher).

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    So, I turned on auto A/C, dialed temp down to 65 IIRC, turned auto off. Cool air started coming into cabin and saw FE guage go up a couple 10th's.
     
  2. Submarine Dude

    Submarine Dude Junior Member

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    No need to turn A/C on, just dial the temp down, that'll turn the heater off.
     
  3. dogfriend

    dogfriend Human - Animal Hybrid

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    Even when not in Auto A/C mode, the system will try to maintain whatever temp is set: i.e. if temp is set at 80°F, it will try to maintain 80°F. AFAIK, the difference between Auto A/C and manual is that the fan speed is fixed in manual.
     
  4. Celtic Blue

    Celtic Blue New Member

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    So it's never off?
     
  5. dogfriend

    dogfriend Human - Animal Hybrid

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    There is an Off setting where no air is directed to any of the vents, but when any of the other modes (dash, bi-level, floor, def) are selected, the climate system will try to maintain the set temp even when not in Auto A/C.

    This is noticeable for me when I drive the car in the early morning; if I had the temp set at 76°F, and the current temp is only 66°F, then warm air will blow from the vents even though Auto A/C is off.

    This also means that the car will run the ICE (when the ICE is cold during warmup) when waiting at a stop to provide warm air to the climate system. If you run the temp down, then the ICE will shut down when warm air is no longer needed.
     
  6. cycledrum

    cycledrum PSOCSOASP

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    That is true if a fan speed is set. No temp displayed if fan off.
     
  7. dogfriend

    dogfriend Human - Animal Hybrid

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    You can adjust the temp up or down with the steering wheel controls, even when Auto A/C is off.
     
  8. cycledrum

    cycledrum PSOCSOASP

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    Thanks. I drove around and became more familiar with the climate system.
     
  9. cycledrum

    cycledrum PSOCSOASP

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    If a fan speed is set, yes.
     
  10. ETP

    ETP Ancient sloth foot

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    If you did what I did and set the temperature too high, the electric strip heater will kick on and you will smell burnt wires in the morning. I thought I had an electrical short!:mad:
     
  11. Celtic Blue

    Celtic Blue New Member

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    I always run with the fan set to 1 or 2 or off. I don't trust auto.
     
  12. cycledrum

    cycledrum PSOCSOASP

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    If running A/C at low fan setting, is it less strain on system to select recirculated air? (since it won't have to cool hot outside air)

    I know this has been asked in other threads. My '88 pickup owner's manual says recirc should be used when cooling cabin down, then use outside air.

    I know the Prius auto system uses recirc for low temp settings, but switches to outside air at higher temp settings.
     
  13. alanh

    alanh Active Member

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    There's actually several degrees of "auto" -- air conditioning available or not, fan speed, and temperature. Each can be turned on or off individually -- in full auto, the computer controls all of them.

    1. Manual fan speed: set a fan speed.
    2. Manual A/C: deselect A/C button, A/C won't come on.
    3. Manual temperature: set the temp all the way down to "LO", heat won't come on.

    If you do all three you get a "vent" setting where it doesn't do anything but blow the fan at the speed you select. No heat, no A/C.
     
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