How much does your ac affect your mileage?
 

I haven't updated my vehicle mpg here in a long time but I keep track of it vigilantly at home. My 2008 ranger 2.3 5 speed rwd averages 27.6 over it's lifetime. Upper 20s low 30s in warm weather and 24+ tanks in the winter. My biggest killer seems to be the AC in the summer though. I try not to use it but I've always had an issue with heat. I wear shorts and t shirts year round even below freezing. But anything above 75 is uncomfortable and anything above 90 is almost crippling to me. I only use my ac when it's above 83ish but it hacks about 6mpg off my trip home from works average. Is a 20% loss common? I had my ac checked/serviced last year but they said nothing was wrong with it. Seems like it really kills power in my little truck too. What % loss is your ac in your vehicles?

Before my engine swap, 25% was a realistic loss in fuel economy, but I don't have a baseline with the new larger engine. Running the compressor adds close to a fixed amount of fuel consumption so the less fuel you're using overall, the larger the percent loss in economy.

Open windows create drag.

Those windows open also increase fatigue via wind noise, dust, pollen, vehicle exhaust, etc, being pumped thru the vehicle.

Being fresh and alert at the end of the trip counts for more than some tenths. Against the ANNUAL average mpg, what’s the penalty? 3/100’s of a cent?

HOW you use the vehicle will always come first. And I doubt anyone has dead-lowest usage charted except for a minimal period.

A car is about convenience. Designing one’s life so that ownership is NECESSARY is the problem.

What (in your use) would some further discipline gain in terms of fewer engine starts? (No one thinks twice about turning a light switch on or off. The car is a whole different set of penalties to turn on per convenience. You aren’t walking thru your home with a flashlight to avoid engaging the main, are you?).

Track the number of engine starts per per week. Isolate the cold ones (after four hours). And get Average MPH to a higher number.

A/C is a great tool. Keeps one from having to change clothes at each destination. Etc.

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Audi A3 2012 1.6 tdi.

Shows AC consumption.

Depending on how hot it is outside. It is consuming between 0.3 to 0.7 liters of diesel per hour.

Per hour in my opinion is the correct way to measure it. Then your equations for travel might favor a very slightly higher speed.

20% doesn’t seem out of order, really.

I believe that a/c drag increases more slowly than engine output as you go from smaller to larger vehicles, so smaller vehicles tend to take more of a hit than larger ones. My Echo and Civic both take pretty big hits, similar to yours, where my wife’s Town + Country, at roughly 2.5x the displacement, interior volume, and engine output, barely even registers a drain, probably on the order of under 10% (I don’t drive it enough to really know). Granted, it’s nearly two decades newer, so that probably helps vs my Japanese beaters.

Using percentages of mpg is wrong in my opinion.

Galons / hour would be a more appropriate measure.

Liters per 100-Kilometers covers a wider span of use. With boats and airplanes, I’d agree about Time having precedence.

Sorry, though, this is the USA. We should have converted to metric in 1903. Rationality wasn’t part of that false resistance to a needed change. Efficiency & Clarity don’t impress us.

In the meantime, noting a fuel burn penalty as a percentage is partly dependent on knowing what is possible for that vehicle (and conditions). Being off from previous by 19% usually means a vehicle problem.

But, just getting others to record annual gallons is heroic.

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I checked my gallons per hour at idle and speed with closed windows, open windows, and closed with ac on. At idle the AC kicked it up .25 gph. At 35 it was about .27. And when I checked at 65 it looked about .3

Seems to increase even more on hills. Maybe because my truck doesn't have much power as it is and it's giving it up for the ac

Oh and windows down showed almost no effects on my gph

Side note I just read somewhere that a normal car AC system is a 5 ton 60,000 BTU system. So even if everything was 100% efficient in getting 120,000 BTUs out of a gallon of gas that would be 1/2 gallon per hour at full load. That takes a 30 mpg car at 65 down to 23 mpg. Luckily I don't think it needs 60,000 BTUs continuously. I wonder if better insulation would do more to limit heat gain/cooling loss would help much.

Pretty sure my AC needs a recharge, but I don't really know because I haven't tried using it since last year when I test drove the car before buying. So my AC loss is 0 MPG. :p But I presume I would see a significant loss were I to do the crazy thing and refill the AC and actually use it...something I can't fathom doing. :rolleyes: Windows cracked at <40 mph speeds on hot days keeps the interior cool enough, and just the fan on low at higher speeds if it gets hot enough, which it hasn't yet. There's also a slight forced airflow through the vents on my car with the climate control off that keeps the car cool (and warm during the winter) as well. The gray-ish beige interior also seems to stay a lot cooler than the gray cloth in my Civic.

I also like the heat and rarely have a passenger in my car.

There was a MPG loss with the AC running on the Civic I used to have, but I have no idea how much it was due to no actual testing and too much variance and inaccuracy with Torque's fuel economy instrumentation. Plus, I never ran the AC in that car even though it worked fine. I even removed the blower motor for weight reduction...

That's not how an A/C works. The 60,000 BTU is the amount of heat it can remove from the cabin, but the amount of power the compressor needs is some smaller number. The ratio of heat moved to power input is called the coefficient of performance. For a car A/C the COP is between 2 and 6, probably. Depending on operating conditions.
For example, Toyota says their Prius A/C consumes 4500 watts (about 15000 BTU/H) and I guess it is capable of about 60,000 BTU. So the COP is about 4.
15000 BTU/H is about 1/8 gallon of gas.
-mort

I make no effort to measure the loss of fuel economy when running my Mazda3's air conditioner. When the weather is 90 degrees plus and the humidity close behind, who cares? Not me.

Because I live in a hot and humid state, my air conditioner is on almost all the time. If I removed the air conditioner, I doubt my fuel cost per mile would rise much above the 4.6 cents my car has achieved since it was bought new in 2015.

I might do a dedicated a/c summer, but I already decided that I’d rather do a faster transit home from Dallas. Where I might get some data is doing the first few miles on the freeway using a/c to cool the interior plastics and such.

I’m still of a mind that Japanese a/c kinda sucks, but I should use the dang thing now that I recently had to go through the effort of dropping a motor mount to replace my drive belts.

I drive my Mazda3 mostly on long commute trips on the highway, and as already noted, I can't tell the difference in fuel mileage with and without the air conditioner. I try to see evidence of it on the Scangauge via its instantaneous mileage readout, but the variations of highway, wind, etc tend to mask any contrast between "on" and "off" mileage differences for me. I know the air conditioner takes energy to run, but it's small enough that I can't "see" it, either on the Scangauge or at the fuel pump.

One technique I use when I don't have a passenger is to push the button that controls the air conditioner's compressor on/off activation. I leave the thermostat/temperature setting on "maximum cold," and when I get cold, I push the button to turn off the compressor and let the temperature gradually rise until I'm too hot, then repeat the cycle. When I push the compressor button, I can't tell any difference except for the temperature of the air; ie, I can't "see" whether the compressor is on-or-off on the Scangauge or "feel" it via the ambience of the car or in any other way to indicate the compressor is running.

One reason I use the compressor's on/off button in this way is the fact that at one time in automotive history (and maybe today in some cars?), some genius figured it was a good idea to let the compressor run all the time and use the engine's hot water to moderate the cabin temperature. It works, but at a higher fuel price. A workaround for me was the compressor on/off technique. I don't know if it's better for fuel economy on my Mazda or not, since I suspect the Mazda's compressor cycles as needed and doesn't use the "hot water" idea. But, is it better for FE to use the on/off technique or just set the temperature/thermostat at the desired temperature level and let the compressor cycle? Don't know.

In any case, I'm too old to drive around in a tropical climate while being hot and sweaty with the roar of hot-and-humid-and-dirty air blasting through the car for several hundred miles at a stint. I just can't take that anymore. Nosir.

Your Mazda is a lot newer than my old beater. I would expect better a/c abilities. My Ma’s ‘06 Mazda 3 is a mystery, I don’t think I have ever driven it. But my Civic AC sucks, my Ma’s former ‘04 Sienna a/c sucked, and the worst of all was my old Toyota Echo, the only one I checked with an actual manifold setup.

So, given that my dataset is old, i’ll say that 90s/early 2000s a/c royally sucked.

I did some data logging which I will try to post once I get back.

My cars AC causes about 10 newton meters of drag torque to the engine when on coldest. (I will compare it to the engine torque produced later)

In car display says 0.7-0.8 liters of diesel per hour.

It reports this value even when the car is in dfco mode. And it appears to be a pre estimated value.


Car is audi a3 1.6 tdi 2012 with 200k km.

It’s not temp modification so much as it is humidity control. It’s also an extra level of dust removal. Start with air on Recirc, move to Norm, and then to Bi-level. Crack a rear window slightly until that last change.

Control over humidity while parked is a goal for you. Given shade (no direct sun) the A/C load is then minimized.

Plenty of legal window tint the other. 3M makes a huge variety ($ to $$$$) and it’s likely you’ll need to head to Houston or Dallas for the right installer for the good stuff. Quality matters. (I use REFLECTIX press-fit interior shades cut from the four foot tall rolls for my pickup & big truck. Use the windshield one EVERY time you park while on errands).

Inspect the door & window seals. R & R as needed.

And, yes, a sheepskin seat cover (medical grade) helps.

Every vehicle takes 1.5-hrs to warm-up (tire pressure equalization). 45-miles just to get oil to operating temp. Coolant temp means little. Its burning off the accumulated crankcase acids that counts, thus trips under three hours are to be avoided.

As a member of EM it (should) be fair to assume you’ve eliminated the multiple short trips you may have once made as a matter of course.

Thus long trips are highlighted for highest average mph as a greater percentage of use.

HVAC use is BEST for highway as airborne pollutants are reduced. Fatigue via wind noise is reduced.

HVAC is thus a fuel savings as the INEVITABLE onset of operator fatigue recedes farther into the day.

The “penalty” for A/C use correlates with full warm-up and overcoming short trip acids, etc. At three-hours plus, it’s using more than would the heater (per se), but today’s cars aren’t built with dash-controlled kickpanel vents and front vent windows. There’s no “Intermediate” adjustment of exterior-admitted airflow without the HVAC system. (No spring or fall, as one guy said).

As I my post above, what’s the actual ANNUAL CPM penalty? 3/100’s of a cent? A half-cent? Two cents?

Solve for that number.

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According to my Spark EV A/C uses 5% of the total energy consumed on my commute. Heat consumes about 33% but the Spark EV has an inefficient resistance heater.

I wonder why they do not use the AC in reverse like some home AC units.


Should have a similar COP.

Some newer units use a heat pump. My Spark is a compliance car so it was all about selling the required 2,000 EVs per year for the minimum cost.

I measured a 6% hit, based on steady speed testing I did with a Canadian market Nissan Micra (same 1.6L, 109 hp engine & AC components as the 2012-2019 Versa Note & sedan).

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

That 6% hit due to an air conditioner sounds reasonable to me.

I just got off a 400-mile trip in typical-for-around-here 95F weather with the air conditioner keeping me cool in my Mazda3. As I noted above, it always seemed the variables on the highway kept me from seeing a difference on the Scangauge comparing the mileage with the compressor on vs off. However, today the conditions on a very flat section of road let me see that difference for the first time on the gauge. I cycled the AC compressor on/off, and indeed the instantaneous mileage screen showed a several MPG hit with the compressor on vs off.

Usually, variations in the road or traffic or wind made too much "noise" for me reliably to see it on the gauge. Not so today. The differential showed up there.

Today, without the intervening effects of any noticeable wind, with the AC running I got some of the best mileage for my car, 49.2mpg. The only "hypermiling" I do on the highway is speed control, and today I benefited from being able to find a truck that was running about 55mph on a 70mph Interstate over a 50-mile stretch. So, I stuck behind that truck at about a four- or five-second elapsed-time distance for about 50 miles, which let me benefit from the bit of extra mileage without attracting the hatred of those who were passing us at a 70 - 80 MPH clip. Without the truck for them to blame, I would have been running much faster for sure.

So, I know the air conditioner cost me some MPGs, and the Scangauge confirmed that today. I just don't know how many MPGs I lose, as asked by the OP. Because I live in a tropicalesque climate, the air conditioner runs the vast majority of time, and my Fuelly records don't show much difference in mileage winter-or-summer that could be attributed to the air conditioner; at least as far as I can tell.

I have had people furiously insist that air conditioning does not decrease fuel economy. Really? Electricity bills are ridiculous during the summer specifically because of the air conditioning, except you are relying on a gas-powered generator?

It is amazing how people use wishful thinking to justify their decisions.

I think the reason some people say that the AC does not decrease their fuel mileage is the standard comparison between a car on the highway with the windows rolled up with the AC "on" vs that same car with the windows rolled down with the AC "off."

Yes, it costs to run the AC compressor, but the aerodynamic hit that results with the windows rolled down costs too. It is often said to be a wash. So why not stay cool.

Of course, a die-hard hypermiler can make the point that one should drive with the windows up and the AC off for maximum fuel economy. That might work for the hardiest of us, but you could be arrested for doing that with children on board. :-)

I only use AC with passengers. I was in Phoenix yesterday and had my windows down when I was not on the highway.

For some reason I drank a quart of something I picked up from the dollar store and a gallon of water in one day.

You could argue I ran off refrigerated water. I do not know how much gas I saved, but refrigerated water is cheap!

The gas-powered generator is already running. Adding A/C what with today’s efficient systems isn’t much of a burden. I think you need to revisit that one.

Fire off a 7-liter Chrysler with an RV-2 compressor and IT IS 10% or better at speed. (It required matched drive belts. Literally cut from same roll and next to each other). Up to 20% around town. The competitors weren’t really any better in the 1960s - ‘70’s.

But one could open vent windows, and floor vents to modify airflow at speed. Windows opened about 1-2”. Fall & Spring. Not forced to use HVAC like today.

It’s the same problem as today, though, where folks DONT account for slow speeds & idle time. That 70-mph trip is more like an average 57-mph. Failure to understand their own driving. And those slow or stopped moments can cook you.

An EM driver counting pennies would start up the air conditioner as he exits the highway. The small on-highway savings would underwrite a fair amount given a great distance covered (were fatigue not a factor).

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