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Thread: AC vs. MPG: impact of air conditioning on fuel economy tested

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    Administrator MetroMPG's Avatar
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    AC vs. MPG: impact of air conditioning on fuel economy tested

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    How much extra fuel does the Micra burn running the A/C ? ENQUIRING MINDS WANT TO KNOW!

    Just for kicks, I did a series of bi-directional averaged runs at 3 different speeds with the A/C on and off.

    I set the fan on the 2nd speed and left it there for all runs, just toggling the A/C switch.

    Here's what I saw:

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    The average fuel consumption increase with A/C on vs. A/C off was 0.3 L/100 km or 5.9%.

    Here are the raw numbers...

    Code:
    speed   AC      N.      S.      avg L/100 km*
    
    60      off     4      4.1      4.05
            on      4.3    4.4      4.35
            on      4.3    4.5      4.37
            off     4.2    4.1      4.16
                            
    80      off     5      4.5      4.75
            on      5.5    4.7      5.10
            off     5      4.5      4.75
                            
    100     off     6.3    5.6      5.91
            on      6.6    5.8      6.15
    
    (* Some of the averages are affected by rounded conversions of initial 
    readings that were taken in MPG)



        __________________________________________

        click to view fuel log View my fuel log 2015 Micra S manual: 5.0 L/100 km ... 56.5 mpg (Imp) ... 20.0 km/L ... 47.0 mpg (US) ...


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    Daox (08-21-2014),icefly (10-28-2015)

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    Senior Member Howie's Avatar
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    Thats pretty awesome.. Now you have to do the mythbuster thing. Do that same test with all the windows down! (testing drag)

    But the AC doesnt seem to suck too much fuel but there is definitally a difference!

        __________________________________________

        click to view fuel log View my fuel log 2015 Micra S automatic: 7.9 L/100 km ... 35.7 mpg (Imp) ... 12.6 km/L ... 29.7 mpg (US) ...


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    Administrator Daox's Avatar
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    6% is pretty significant. Just imagine adding 6% to the price of fuel by pushing a button...

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    Administrator MetroMPG's Avatar
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    Quote Originally Posted by Howie View Post
    Now you have to do the mythbuster thing. Do that same test with all the windows down! (testing drag)
    Yeah - not enough time with the Micra! Feel free, though.

    But we probably all know the rule of thumb: at low/mid speeds, windows down is better (more efficient) than A/C.

        __________________________________________

        click to view fuel log View my fuel log 2015 Micra S manual: 5.0 L/100 km ... 56.5 mpg (Imp) ... 20.0 km/L ... 47.0 mpg (US) ...


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    Junior Member MicraJordan's Avatar
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    Quote Originally Posted by Daox View Post
    6% is pretty significant. Just imagine adding 6% to the price of fuel by pushing a button...
    Dammit... that's good perspective. Now I'll have to think twice.

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    First post to share some A/C experience with you folks.

    For the Nissan I've owned, Nissan Sentra SeR SpecV 2002, Nissan Versa 2008 and my current Nissan Cube 2009, they all show the auto AC at ''ON'' when selecting the windshield or windshield/feet.

    You can turn it ''off'' while pressing the AC button, but, the compressor is still running down there if you leave the selector at either feet or windshield/feet.

    So in the end, the engine still required fuel to feed that ''need'' of AC even if you didn't ask for it.

    ---

    Admin note: I split the discussion / demonstration about how to disconnect the A/C switch from the defrost settings to a new thread.


    Thread: DIY: disconnect air conditioning switch from defroster setting

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    Senior Member dani3d's Avatar
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    Well, if I put 25$ in my car per week, and it would cost me 26.50$ instead to run the AC and be comfortable, I would use the AC for sure. Not enough difference to be a big deal, even if I care about fuel economy. But if the thing keep turning ON when all you want is heat, then it's very anoying. 6% more is anoying when we don't need the AC and forget to turn it off.

    But I am not so bold as to cut a wire and risk voiding my warranty.

        __________________________________________

        click to view fuel log View my fuel log 2015 Micra SR automatic: 7.0 L/100 km ... 40.4 mpg (Imp) ... 14.3 km/L ... 33.6 mpg (US) ...


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    Senior Member dani3d's Avatar
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    Something hapened. At first it was much warmer outside and I was getting 6.8 average l/100km. Then as the temperature went down I was getting less and less. Last week I was getting 7.2 average l/100km. Then Tuesday here it was -9C in the morning. I got to fuel and reset the average l/km, drive to work and back and to my surprise it now show 6.5 l/100km average. When I reset it, the average went way up to 16l/100km because the engine was cold and all the red lights etc...but after warm up and short ride on the highway it went down to 6.5 and pretty much stayed there since then.

    So what hapened? Did my engine finaly broke in? or was the fuel that I was putting in before mixed with water? I always gas at the same place though, so not sure if that's the case.

    Is it possible that the oil became thicker with the colder temperature and that helped the metal to metal contact, giving better fuel economy? Not sure yet what to make of it. I will see with time but now I am getting 6.5 instead of 7.1 l/100km. Now this is much better! I am driving the same way since day one, eco-driving.

        __________________________________________

        click to view fuel log View my fuel log 2015 Micra SR automatic: 7.0 L/100 km ... 40.4 mpg (Imp) ... 14.3 km/L ... 33.6 mpg (US) ...


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    You just get less MPG when it's cold out. Both our Micra and Elantra have lost like .3 to .5 l/100km's.

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    Senior Member AlphaMicra's Avatar
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    Automatics are terrible for fuel economy in the cold, as they won't lock up until the engine warms up. The colder it gets, the longer it takes the engine to warm up, so the longer it takes before your transmission can lock up. As for my 5 speed manual, not much change in fuel economy.



    In our culture obsessed with absurd excess, the Nissan Micra is my counterculture car of choice.
    Be sure to visit my blog at mymicra.com!

        __________________________________________

        click to view fuel log View my fuel log 2015 Micra SV manual: 6.4 L/100 km ... 44.3 mpg (Imp) ... 15.7 km/L ... 36.9 mpg (US) ...


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