AC commits pre-meditated murder on MPG

I don't disagree that you lose MPG with the A/C on. What I am saying is that the loss is less than with almost any other vehicle when you do the math. It's just that those high numbers (40-55mpg) make the loss seem higher. Most people see a 7mpg loss and they think it's the same as losing 7mpg no matter what your average MPG started off at. A 7mpg loss is huge when you are only getting 20mpg but it it is not such a big deal when you are getting 50mpg. That is why percentages work better. [/QUOTE]
I SEE SAID THE BLIND MAN

 

You're not blind. Unless it is due to those beautiful Greek women.....

 

I still don't like percentages for this. 10% loss on an SUV or full size pickup still represents far more fuel, typically 3 to 4 times more gas, than 10% on a Prius.

Gallons per 100 miles puts it into more meaningful perspective.

 

I have no arguments there. The gallons per mile measurement is superior.

 

Well after 10 pages of this "twaddle", which after 10 pages is what it has become. I find something to agree with, and in a "home boy"! Here's my H.O., the extreme hot is greater this year. My mileage "hit" is greater this summer, alarming it seems, compared to last summer. Now some thoughts as to why. Last summer we still had another car, a Camry which was used a lot as the "grocery getter". Thus not so many trips to several shops over a few hours. Getting into a car that has set on an asphalt parking lot for even a short time, leaves a lot of heat buildup to overcome. Do this several times over a couple of hours and your not going to be getting anything even near to 48mpg! My present tankful of fuel is returning, if I'm lucky, 42mpg, (indicated, MID), so we know it is even less actual. Now a dichotomy,..... previous tank, I drove 170 miles on, then topped up, just to see how I had done.....65.1mpg. Why the difference? Most/rather some of the parameters were the same. I'm one of the EARLY baby-boomers, I didn't have an air-conditioned car until 1972, so I've got it!, I'm going to use it! Especially in triple digit temps! I used ECO mode for 7months when I first got the car, turned it off after that and thought I had a "performance" car,......I've never gone back! Mileage IMHO is no worse for it.
Ok, I run the A/C on Auto, set to anything from 74 to 76, the later will be set after the cabin cools off. On the 170 mile journey I set the cruise at 60mph, never took it off cruise until I left the turnpike. The A/C is set the same when going to the "shops", and so I expect to have less FE. Now let me say this: My "worst" gas mileage is better than most any other cars "BEST". The only way in this summer heat that I'm even going to match my mileage is to ride a Lambretta scooter. Which might be fun if I was 30, but not at the age I am. That's what I like about this car is it takes care of it's self, a lot more economically, and reliably than any other I know of.

 

Lambrettas offered excellent AC too. When I couldn't sleep during sweltering Boston nights I used to get on my Lambretta 150 and ride it around to cool myself off. In those unimaginable years before AC was widely available.

 

After reading 11 pages of AC use, I feel like an oddball for running auto at 80 degrees and being at 1-2 bars in 10 minutes...
in 110-115 degree temps...

 

In that kind of heat, MPG be damned - Turn on the A/C!

 

I just went on a 190 mile trip in my mom's 2011 Camry Hybrid with the A/C on and set to 70F on auto mode (ECO enabled) and still managed to hit 49.4 MPG for the whole round trip. The half of the return trip I maintained 78.4 MPG (89.8 MPG at 70 miles into the trip), so I'm not sure using the A/C always costs you that much mileage in one of these hybrids, but it probably depends a huge amount on the driving conditions.

 

Living in Houston, a/c is a must. Temperatures exceed 90, even 100, in the summer (which itself is longer than most people's). It's not even a dry heat. Cracking a window doesn't begin to cut it in is environment. I lost a/c on a car once on a road trip, and it was a very inhumane drive back home. So houstonians can expect regular hits. Of course, one still does better in a Prius than in anything else.

But today, I upped the temperature setting, which was too low. It'd never have occurred to me to reduce a/c in previous cars unless I was actually too cold. I may try Eco next. I've only had the car a few days and am already becoming conscious of how what I do affects the car. Like easing off the pedal a bit when I see it nearing the power bar.

 

I played around with the AC today. I drove for approx. 30 miles with the windows down to air out the cabin but ambient temperature was 100°. I then turn on the AC . I used the auto setting and set the temp for 70°. I observed the usual 10mpg drop in mpg but this time I left the AC on until the cabin cooled down. For the next 15 minutes the AC stayed on full blast trying to get the cabin down to 70°. I kept turning the AC off then back on and the mpg always dropped by at least 10mpg. I ended the trip but never successfully cooled the cabin down to 70° therefore the compressor stayed on full blast the entire time.

This leads me to believe that drivers who try to use the AC at very low settings in very hot ambient temperatures will suffer a dramatic drop in mpg on short trips. Longer trips may suffer less but dropping mpg by 10 or more for 15-30 minutes is going to affect mpg total on that tank. This is especially true if you do this every day.

 

At 95 F, it takes me about 30 miles to get to 71 F and start ramping down the fan speed By 55 miles I will be under half way. On days I drive over 70 miles steady, it gets quite pleasant in the cabin.

 

The AC's effect on your mileage is really dependent on the overall vehicle speed I have found.. If you are doing a lot of stop and go/driving at 45mph or below it will kill your mileage because it is draining the HV battery. Same can be said when running the AC at long stops, or parking lots... If you are at least going I'd said 50ish to 65-70 then you can run the AC all you want because the generator is running at a high enough RPM to keep the HV battery at a constant level/supply the car with all the power it needs. So for me it is a rule of thumb to not run the AC when I am driving on roads that are 40mph or less, and I shut it off when I am stopped in traffic for long periods. My average so far on this tank is about 55.4mpg give or take. Was up almost at 60, but then the heat in FL like everywhere else..

 

Thanks, Jimbo. That jives with my testing.

Have you actually tested this? I have and the results are the same regardless of speed. From 70mph to 40mph the drop was consistently 10mpg.

 

Great video F8L! I'm surprised that the fan speed didn't matter, guess if I'm going to put the AC on I might as well go ALL ON!

 

I found that odd as well but the fan, is separate from the compressor so I guess it makes sense. You are asking the system to cool the car down, to a certain temp and the further the actual temp is from desired temp the harder the compressor has to work regardless of what you set the fan speed for. So I would think keeping the fan speed high would helps the car to cool faster thus reducing the amount of time the compressor is maxed out.

I have only been using the auto mode so maybe things work different on manual settings. I will test that out on Monday and report back.

 

I do not have a scan gauge or anything of that nature. So as far as officially "testing it" I have not. This has been my observation though after owning the car since February, and putting almost 10,000 miles on it as of this week. If I go out on 9A and fully charge the battery, and come back to where I live, and just sit in the parking lot with the AC on it will drain the battery quick. If I go back out and recharge the HV battery, and then drive up/down Hodges Blvd with the AC on (35mph road) the HV battery drains quickly as well.. If I again recharge the battery by going out on 9A, and then drive on regular roads with speed limits around 45mph or so then the battery drain is not so bad. It continues to get less, until finally you go on say I-95 doing 70mph where you can run the A/C all you want to seemingly no effect at all.

I do agree with what you are saying about the AC having little effect in itself. Is proabably true.. The problem though comes in when the compressor is drawing down the HV battery, and the HV battery is helping assist the gas engine to get better mileage. Whenever you hit that tipping point (to me it seems to be with about 3 battery bars left) the gas mileage gets pretty bad (for a Prius anyway) down into the high 40's when as I am driving it is trying to put more power into the HV pack than it is using. Ideally what I have found is you want to keep the HV battery in the top 2 bar range (with that last line left black at the very top beneath the poles on the display), and this will allow me at a steady state on a flat road to show about 75mpg on that mpg display to the right of the speed which is how I manage to average about 54 or so mpg per tank on average with the few red lights I have on my way to work..

These are just my observations based on driving the car everyday from the last few months. I am sure you guys have a lot more knowledge than me as I have never hooked anything up to the car.. From reading everyons write ups though on how the ICE/MG1/MG2 work together, and the purpose of the HV & 12V batteries I have just deducted my best thoughts on how it all works... Everyone should try it though.. If you are going 50-55mph or faster run the AC full blast, and the HV battery will still re-charge, and it will not effect the mileage but a small smidge.. Then try it all the other ways.

 

After doing some more thought figured I'd chime in on this since I ONLY use manual mode. The cabin fan is seperate from the compressor, and does not drain the HV pack so I run the cabin fan all I want. In manual mode I can select where I want the air to draw (either outside or recirc), choose the fan speed, and then choose the cabin temp manually. I think in auto you just set the temp and the car takes care of the rest (which is why I have the temp up/down arrows on my right steering wheel pad). As far as leaving the fan on max I am unsure if that is faster to actually cool the inside of the car. I leave it on max, but it seems to take the AC compressor a long time before the cabin starts cooling (or maybe it's the 100+ days we've been having here in Florida). I think ultimately how fast the cabin cools is going to depend on the temp you start at. I highly recommend people get those foil reflectors even though they are a pain in my rear to put in. They help not have to work the AC as hard in my experience. Car still winds up being hot, but just not to the point where I can't touch anything. I am really debating putting on that remote start so I can start the car/have the AC running for a couple minutes before I get off of work to try and help.

 

I live in the Nevada desert. I recenty had occasion to make the same highway trip (Las Vegas to Laughlin) twice in the same day. Once durinf mid day, and once at night. I don't recall the temp difference, but it was cooler at night (still in the mid nineties). I noted an increase of over 4 MPGs at night.

I think, in addition to the ambient temp, that the sun shining in the nice, flat windshield and backlight works the A/C hard. My windows aren't tinted, but I think they're gonna be soon.

I wonder what the effect tinting will have on MPG. Living in the desert (Laughlin is hotter than Vegas) will make it easier to determine the difference.

Damn, it's HOT out here......

 

Roadburner440,

I think we agree in general. On the freeway you take less of a hit than at city speeds as long as you are traveling long enough for the cabin to cool off. Otherwise a short trip on the freeway with the AC on high will create a 10+mpg loss until the cabin cools closer to the set temperature. The one caveat to this idea is that when the AC is on and running fairly hard, it is harder to enter a glide where your ICE is off and you are running on minimal battery power. This works when you are going over large overpasses or hills. When the AC is on and still trying to cool the cabin down, I can rarely enter a glide. The ICE simply stays on. Once the cabin is cooled down and the AC compressor is not working so hard I can then enter glides again but this is after at least 20 miles when the temperature outside is 95 degrees or higher. The AC also runs the HV battery down more than without AC such that your SOC may be too low to glide. I have found this to be true once the SOC gets to 57.5% or less. This has an effect on MPG as well if you are the type to utilize this hypermiling technique.

If it is still close to 100 degrees tomorrow I will try to use only manual mode instead of Auto mode and see if my testing holds true. If manual mode doesn't induce the same MPG hit that I observe in Auto mode then everyone should be made aware. I doubt this is true though as during my testing I would adjust fan speeds and that drops you out of Auto mode. I still observed the 10mpg hit when I did this.