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Discussion Starter · #1 ·
If I run the AC with the fan at 1 or 2, will I get less MPGs on mileage?
It's getting hot here now.
 

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I believe it does since the a/c compressor puts a small amount of stress on the engine. With that said, I leave it to the other guys here that know a heck of a lot more than I do!
 

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It's negligible...and if you open a window, then the drag will take your mileage south! I still get in the low 40's going 72 mph and A/C on. :grin2:
 

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Discussion Starter · #4 ·
My 2003 Sentra used to feel like it bogged the engine down to run the AC.

I plugged a 16 GB flash drive into the USB port the other day with about 8 Alan Parsons Project MP3 albums on it, including Time Machine and Keats. The sound I got was amazing. Since then I've been playing that a lot in the car. You can hear it much better with the windows all closed but it's too hot for that this time of year.
I tend to want to run the car with no AC if I can stand it. I always figure it will be less stress on the cooling system and engine to run it without AC.
But after picking wild berries and having sweat run down your face, the AC sure is nice sometimes. :) The Super Tech 5w30 full synthetic seems to be holding up OK.
 

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My 2003 Sentra used to feel like it bogged the engine down to run the AC.
I plugged a 16 GB flash drive into the USB port the other day with about 8 Alan Parsons Project MP3 albums on it, including Time Machine and Keats. The sound I got was amazing. Since then I've been playing that a lot in the car. You can hear it much better with the windows all closed but it's too hot for that this time of year.
My Accent definitely bogs with the A/C on but once I get cruising it's not too bad. Love Alan Parsons' music. Some very underrated music there.
 

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It shouldn't matter what speed the fan is set to. It's not the speed of the fan that costs fuel mileage, it's the compressor running. How much the compressor runs is unrelated to the fan speed.
 

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It shouldn't matter what speed the fan is set to. It's not the speed of the fan that costs fuel mileage, it's the compressor running. How much the compressor runs is unrelated to the fan speed.

While that's largely true, it's not completely true.


The amount of air flow through the evaporator will affect how much heat the AC system is removing. The more heat removed, the more work it is doing, so the harder it is for the engine to turn the compressor. That said, the difference in compressor load from low fan to high fan is pretty minor, and it less than the difference in load between a warm day and a hot day.
Also note that the fan itself is not free. The power to run the fan comes from the alternator. The more power the alternator has to produce, the harder it is for the engine to turn the alternator.


All that said, the use of the AC and the fan is a very minor reduction of gas mileage. If you want the best mileage at the cost of everything else, get a bike.
 

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AC on = more engine work = less mpg. Basic formula is pv/t = pv/t
...couple things you're not considering...compressor isn't always on (unless Max'd), and if you open a window for air circulation...you are loading the motor from the drag.
It comes down to..."Is my comfort worth a couple pennies a mile?" Again, open a window and you'll probably waste the same amount as with air on!
 
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I believe it does. And it could be quite substantial than what people normally tend to believe. I'm driving 2017 Hyundai Sonata



I have observed my mpg going haywire recently when I started using AC on a 30-mile per way commute to work. In the morning, it is 2-Fan, 3/5 Thermostat. and 3-Fan, 4/5 Thermostat on the way home.


I also think that the carbon build-up has something to do with the inefficiency in the mpg.


I would like to find out whether it's one or the other, or both, but I won't try to bake myself.


Sorry.
 

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In general with newer cars at higher speeds (20 mph and above) milage will be better with the AC on then with the windows open due to aerodynamics
Completely agree with this. Most modern cars fall into this category. Modern A/C compressors also require significantly less energy to turn under load then they did in the past. I’d agree at least on the interstate having your windows open probably would hurt your mileage worse then using A/C. Regardless you are talking about maybe less then a dollar per fillup to use it so does it really matter if it burns more?
 

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With my Accent I get better mileage in the summer using AC than I do in the winter with the cold.


The Gen Coupe there is no difference but I seldom drive with the windows down.


I put small LEDs that are grounded when the AC relay coil is grounded to see when the compressor is being powered. With the newer type compressor this would not work. On the Accent it seldom cycles though does with every manual shift. The Gen Coupe is only on maybe 20-30% of the time when it's running.
 

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Good grief turn your b****y air con on and be comfortable in your car. You will not notice the difference in you MPG.
_itch_? Not sure of the vernacular where you are! :grin2:
 

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...and that's what they say instead of pha-king...got it! I'm slow today! :blush:
 
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While that's largely true, it's not completely true.


The amount of air flow through the evaporator will affect how much heat the AC system is removing. The more heat removed, the more work it is doing, so the harder it is for the engine to turn the compressor. That said, the difference in compressor load from low fan to high fan is pretty minor, and it less than the difference in load between a warm day and a hot day.
Also note that the fan itself is not free. The power to run the fan comes from the alternator. The more power the alternator has to produce, the harder it is for the engine to turn the alternator.


All that said, the use of the AC and the fan is a very minor reduction of gas mileage. If you want the best mileage at the cost of everything else, get a bike.
Good points. I guess the takeaway is that the speed of the fan does negatively impact fuel mileage, but the difference is negligible.
 
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The low speed fan should not be running when above 30 mph or so.
 
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