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Discussion Starter #1
Now that we're in the heat of the summer I use the A/C a lot... okay, all the time :roll:

OUCH!

I'm half way through this tank and sitting at 41.3 average. I usually average between 46-48 mpg on each tank. That is a pretty big hit for turning the A/C on.

What experience have the rest of you had with this?
 

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90+ percent highway driving, a/c on all the time. 50-52 mpg. I refuse to be uncomfortable on a 70 mile round trip commute (or any time, for that matter).
 

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I've had the same experience, especially since I've been doing a lot of short city trips back and forth to my summer job, and practically no highway driving. My solution is simply to leave the windows open since I'm going slowly - a little fresh air does you good. The mileage drops stopped after I started this.
 

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A/C will hurt you big time in local driving, but should have a minimal hit at highway speeds as the ICE will always be running anyway.

This is especially true in a normal car or a pre-04 Prius that has engine driven A/C. But even with the electric at 60 mph it will cost you very little gasoline to produce the electricity to run the compressor. It will actually cost you more to drive with the windows open at that speed due to resistance.
 

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I leave mine on Auto A/C year round set at about 73 degrees. My average so far on my 04 is 45 MPG. There are a lot of short trips in that lifetime average, so I don't think the A/C is that big of a hit.
 

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Very big hit. It's been in the upper nineties every day in Tidewater Virginia, and I keep the A/C set to meat locker. Only take short trips in town ( a tank of gas usually lasts me 3 weeks). Present tank at 120 miles averaging only 38 mpg. DOD
 

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I agree with firepa63. The A/C is installed for driver and passenger comfort. It costs extra on most cars and some can be orered without it, but in this day and age very few are. (order one without it and there goes the resale value) It is true you might receive some comfort at slow speeds by opening windows but long proven you do better with milage using the A/C on highway speeds because of the remakable difference in "drag." I use mine at all times and still get my overall 45 MPG. You can "mickey mouse" it like extra high tire pressures ect: in that elusive hunt for more mpg but is that the way you really want to live?
 

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dod said:
Very big hit. It's been in the upper nineties every day in Tidewater Virginia, and I keep the A/C set to meat locker. Only take short trips in town ( a tank of gas usually lasts me 3 weeks). Present tank at 120 miles averaging only 38 mpg. DOD
I could have written this. Nearly same weather conditions here. Short trips + AC=significantly lower mileage. I was at 40 on my last tank.
 

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Since I took delivery of my Prius two months ago and since I'm a New Yorker transplanted to TN, I run the A/C full blast constantly. As a matter of fact, I've never turned it off. My geographical area is very hilly (the foothills of the Smokey Mountains, actually) and I still average between 48 and 51 mpg.
 

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A/C impact on mpg

Phoenix AZ
Spring & fall highs = 65-75 (no A/C)
Average summer highs = 110-116+ degrees (constant A/C)

2002 Prius
Spring & fall mpg - 51-53.5 mpg
Summer = 41-43.5 mpg

80% city driving in suburbs @ 45 mph.
 

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More data from Phoenix

I also live in Phoenix, and have my A/C set at 80 degrees (just like my house). I know that sounds high, but compared to 115 its cool!

Conditions:
50 miles freeway driving per day

1994 Prius
winter/spring w/o A/C: 54MPG
summer A/C on low(1st tick): about 52MPG - needed 85-100
2nd & 3rd tick: about 50MPG - needed about 100-100 degrees
4th tick (med): about 45MPG - needed about 110 degrees
high: about 25-30MPG - I never use that setting, because it kills me to see my mileage go that low! :oops:
 

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I see the mileage hit. 46-48's down to 40-41's. I could care less. I still get over 400 miles a tank and thats all I care about. No way will I sacrifice comfortability for better mpg's. I usually have my A/C Auto set to about 74-77.
 

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One factor to consider is how hard the AC is working. If the cabin is close to desired temp, then it is only needed to maintain that temp, and won't work so hard. If you get in the car at 5pm after sitting in the parking lot in blistering heat, the AC may run full power for something like 20 minutes. At full power, the AC does use quite a bit of energy, but to maintain a temperature, not so much.

Think of it as comparing MPG at acceleration versus MPG while cruising at a constant speed.

As for AC versus windows open, crude tests that many of us have done, and even casual observations, have shown that AC seems to take more energy than a lowered window. However, the noise and wind may make having the window open more undesirable.
 

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I've got a Classic Prius so my A/C is belt driven by the ICE vs. the electric AC of the HSD Prius, so YMMV, but I find that once you have the cabin cooled to a decent level, switching to recirc and floor level vents, results in a nice comfortable cabin, with the A/C compressor running relatively infrequently. At this point, if you also turn *up* the temperature dial a click or two, the compressor runs even less and there's no real difference in cabin comfort. Aside from the initial hit when the A/C has to cool down a hot car, when I run floor level recirc with the temperature up two clicks with my A/C, there's not a lot of difference in MPG: once the condenser is cool enough, the A/C will stay "off" and I can still do extended runs of stealth at 98F, and the ICE will stay off through most stop lights.

On the other hand, if I keep the bi-level going, the compressor runs a lot more often- I can't sit through more than about 5-10 seconds with ICE off at a stop light, and my MPG gets a very noticable 3-4 MPG hit (again, this is on a Classic Prius with belt driven compressor). According to the NCF booklet, the A/C ECU seems to use the climate control settings on the console mostly as a suggestion and the computer tries to figure out the best settings, so on bi-level it tries to use more outside air (even if recirc is on).. The outside air is usually hotter than the internal recirculated air, and the bi-level also tends to move more air volume around, which means there's more heat exchange needed at the condenser, and thus the compressor has to run much more often to keep the system cool...
 

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Very big hit. I never let my tank get down to one blinking bar, and still fill up about once every three weeks, so you can see I take a lot of short trips. With the temps running 95-100 here in Tidewater VA, and my A/C set at 72, I'm only showing 38mpg on the current tank. Normally I get 43-46 in town. Have gotten 53mpg on trips in cooler weather. I know I could do better by raising the temp setting, but I'd rather be comfortable. DOD
 

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dod said:
Very big hit. I never let my tank get down to one blinking bar, and still fill up about once every three weeks, so you can see I take a lot of short trips. With the temps running 95-100 here in Tidewater VA, and my A/C set at 72, I'm only showing 38mpg on the current tank. Normally I get 43-46 in town. Have gotten 53mpg on trips in cooler weather. I know I could do better by raising the temp setting, but I'd rather be comfortable. DOD
... or take longer trips.
 

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Right now I have my A/C set to 73 and I do mostly short trips to work and home (less than 5 miles, about 10 minutes each) and run errands. Ah, the joys of not living where you have to use the highway to go to basic places.

Anyway, my last 2 tanks during this rather warm July have been about 48 mpg each. I'm very happy. I'm not convinced that the A/C is all that draining to the vehicle, however as we have learned over the years, your experience may vary.
 

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I have wondered if you would be better off turning the AC to Max, or at least under 70, and letting it run for a short period of time to cool the car, and then turning it off again until it got warm in the car again. It would be somewhat like accelerating and then coasting with the engine off, to follow up on DanMan32's example.
 

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sub3marathonman said:
I have wondered if you would be better off turning the AC to Max, or at least under 70, and letting it run for a short period of time to cool the car, and then turning it off again until it got warm in the car again. It would be somewhat like accelerating and then coasting with the engine off, to follow up on DanMan32's example.
With its massive front window and slate-gray dashboard, the Prius seems to heat up almost instantly with the AC off. Toyota should consider installing some sort of infra-red solar panel on the dashboard: In the summer, it would probably be good for a free mile or two of daily driving. :)

We've experienced a definite mpg hit recently. Last week was the hottest in Colorado Springs' history - one day while driving on a nice asphalt road, the Prius claimed the outside temperature was 108 - and our in-town mpg plunged to the low 40s, which is the lowest it's ever been over any length of time. (But we haven't yet had the Prius during a lengthy cold spell.) Current tank mpg is a little over 50, the lowest we've had on a tank since March.

(Yes, I've become jaded enough to complain about "only" 50 mpg. :wink: )
 

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Discussion Starter #20
Re: More data from Phoenix

Where'd ya get a 1994 Prius??? :shock:

orbops said:
I also live in Phoenix, and have my A/C set at 80 degrees (just like my house). I know that sounds high, but compared to 115 its cool!

Conditions:
50 miles freeway driving per day

1994 Prius
winter/spring w/o A/C: 54MPG
summer A/C on low(1st tick): about 52MPG - needed 85-100
2nd & 3rd tick: about 50MPG - needed about 100-100 degrees
4th tick (med): about 45MPG - needed about 110 degrees
high: about 25-30MPG - I never use that setting, because it kills me to see my mileage go that low! :oops:
 
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