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How Does The Use Of Car AC Affect Fuel Consumption? - Car Talk - Nairaland

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Does The Use Of Air Conditioners In Cars Affect Fuel Consumption? / Does Removing The Thermostat Of A Car Affect Fuel Consuption / How Does Burst Silencer/exhaust Affect Fuel Consumption? (1) (2) (3) (4)

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How Does The Use Of Car AC Affect Fuel Consumption? by tundysho(m): 5:45am On Feb 26, 2008
Could one of the gurus in the house let me know the effect of AC use on the consumption of fuel in automobiles?
Re: How Does The Use Of Car AC Affect Fuel Consumption? by kuntash: 8:22am On Feb 26, 2008
Yea I like this kinda posts, there's this belief that when u drive ur car with AC on, you consume more fuel, that was my thinking too until I watched this episode on ''mythbusters'' on discovery, amazed with the outcome that when an SUV was driven with a/c on and windows down consumes less gas than when d windows are wound up etc, pls gurus in da house , contribute, our Engineer in UK (Sienna-- not sure of d name smiley) ur comment pls.
Re: How Does The Use Of Car AC Affect Fuel Consumption? by adechuks(m): 2:57pm On Feb 26, 2008
Midas, Ivvie, [or vice versa], where art thou ?
Re: How Does The Use Of Car AC Affect Fuel Consumption? by Midas02(m): 5:12pm On Feb 26, 2008
Tundysho,
You can be rest assured that using your AC will always result in lower gas mileage (using more gas). It is simply a fact that using your AC imposes some extra load on your engine and the engine responds by consuming more gas. Do not be dismayed however, lots of things can equally make a car use more gas! - Low tire pressure, poor maintenance, poor aerodynamics, driving up hilly terrain, aggressive driving and even carrying more passengers!. The purpose of buying a car is to enjoy the conveniences and comfort that the car gives you so I definitely would expect AC to be used, extra passengers will ride and hilly terrains will be encountered - that is life!! The most practical mitigations I can suggest is to avoid unnecessary aggressive & racy driving (high revving acceleration), check and maintain your tire pressures at about 40psi all around and make sure you do your oil change and tune ups when due.

Kuntash,
I watched the same episode of Mythbusters and I believe you got the gist wrong. (Season 2 Episode 22)
The objective was to see IF a car with the AC turned on and the glass rolled up, WOULD consume more gas OR less gas than the same car would if the AC were turned off and the windows rolled down. They actually used a Ford Expedition for the experiment and took steps to ensure that all conditions were consistent on a closed circuit track.
Anyhow, the scientific logic was to see if the aerodynamic improvements gained by rolling up windows could neutralize the higher gas consumption imposed by using AC on one hand. And on the other hand, would the better economy achieved by not using AC be negated by the increased drag (reduced aerodynamics) due to rolling windows down.
The conclusion was that despite the aerodynamic edge, the car with the AC on still used more gasoline at certain speed - 45mph and below!. At higher speeds - 55mph and above, it is more efficient to use AC and roll up glass.  So for guys who want to know, it is far more efficient to use your AC at highway speeds - (55mph or 90km/h and above)

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Re: How Does The Use Of Car AC Affect Fuel Consumption? by kuntash: 9:09am On Feb 27, 2008
Midas tanks though, I tot I was sure of wat I saw(not d episode) and it wasnt a FORD. but a Toyota Land cruiser. anyway, ur point was clear, but somehow on that day , Adam & Jamie were kinda amazed at the outcome.
Re: How Does The Use Of Car AC Affect Fuel Consumption? by manuelstud: 4:46pm On Feb 29, 2008
smiley why do i get this feeling that nairalanders are a special breed of auto wizards who happen to be naijamen?
nuff kudos to the viperman,brauneyes,midas,kuntash and ivvies of this word, bigg ups man!!! u guys are tha bomb shocked cool
Re: How Does The Use Of Car AC Affect Fuel Consumption? by mrtunde(m): 5:17pm On Feb 29, 2008
Get this.
Any activity of the car that involves you using more engine capacity, will result in more fuel consumption. It is very logical.

Even something as seemimgly mundane as using your headlights at night.

So i agree with the earliers posts. Tyre pressure, engine condition, aerodynamics, speed, driving habits etc affect your fuel consumption.

But you should not sweat fuel consumption really. If you can afford a ride, you can afford to maintain it.
Re: How Does The Use Of Car AC Affect Fuel Consumption? by gbonsalifus(m): 7:53am On Dec 12, 2012
Read this article on car AC fuel consumption and why you should still use your AC especially in Nigeria http://101carsense.blogspot.com/2012/12/air-conditioner-fuel-consumption.html
Re: How Does The Use Of Car AC Affect Fuel Consumption? by eddy42k(m): 10:32am On Dec 21, 2012
it should also be noted that ur headlights audio player also make ur vehicle's consume more
Re: How Does The Use Of Car AC Affect Fuel Consumption? by ZIMDRILL(m): 10:59am On Dec 21, 2012
Midas02: Tundysho,
You can be rest assured that using your AC will always result in lower gas mileage (using more gas). It is simply a fact that using your AC imposes some extra load on your engine and the engine responds by consuming more gas. Do not be dismayed however, lots of things can equally make a car use more gas! - Low tire pressure, poor maintenance, poor aerodynamics, driving up hilly terrain, aggressive driving and even carrying more passengers!. The purpose of buying a car is to enjoy the conveniences and comfort that the car gives you so I definitely would expect AC to be used, extra passengers will ride and hilly terrains will be encountered - that is life!! The most practical mitigations I can suggest is to avoid unnecessary aggressive & racy driving (high revving acceleration), check and maintain your tire pressures at about 40psi all around and make sure you do your oil change and tune ups when due.

Kuntash,
I watched the same episode of Mythbusters and I believe you got the gist wrong. (Season 2 Episode 22)
The objective was to see IF a car with the AC turned on and the glass rolled up, WOULD consume more gas OR less gas than the same car would if the AC were turned off and the windows rolled down. They actually used a Ford Expedition for the experiment and took steps to ensure that all conditions were consistent on a closed circuit track.
Anyhow, the scientific logic was to see if the aerodynamic improvements gained by rolling up windows could neutralize the higher gas consumption imposed by using AC on one hand. And on the other hand, would the better economy achieved by not using AC be negated by the increased drag (reduced aerodynamics) due to rolling windows down.
The conclusion was that despite the aerodynamic edge, the car with the AC on still used more gasoline at certain speed - 45mph and below!. At higher speeds - 55mph and above, it is more efficient to use AC and roll up glass.  So for guys who want to know, it is far more efficient to use your AC at highway speeds - (55mph or 90km/h and above)

i too so that episode and i knew the results before they even started

if you want to find out with out figures just switch on your car in quiet place listen while it idle then ask a friend to help you by turning the AC while you watch and listen to the engine,the moment you turn the AC the engine will increase ravs a bit and shake a bit that means the load as changed on engine

just remember AC motor is run by the engine then the blower motor also wants power from battery through altanator
Re: How Does The Use Of Car AC Affect Fuel Consumption? by Wallie(m): 7:33pm On Dec 21, 2012
1. In traffic, turn off the AC to save gas, which will reduce the load (work) on the engine.
2. In traffic, AC load has a greater effect on gas mileage than air drag on the car.

3. On the highway at speed, roll up your window to save gas, which will reduce drag (air resistance) on the car.
4. At speed, air resistance has a greater effect on gas than turning on the AC.
Re: How Does The Use Of Car AC Affect Fuel Consumption? by Wallie(m): 7:36pm On Dec 21, 2012
ZIM DRILL:

i too so that episode and i knew the results before they even started

if you want to find out with out figures just switch on your car in quiet place listen while it idle then ask a friend to help you by turning the AC while you watch and listen to the engine,the moment you turn the AC the engine will increase ravs a bit and shake a bit that means the load as changed on engine

just remember AC motor is run by the engine then the blower motor also wants power from battery through altanator

Correct. Once a car starts up and is running, everything is powered by the engine directly or indirectly through the alternator.
Re: How Does The Use Of Car AC Affect Fuel Consumption? by Ikenna351(m): 7:49pm On Dec 21, 2012
A/C doesnt directly place all the load on the engine/crankshaft pulley. Switching on A/C, whether stationally or in motion, places load on the Alternator which creates drag on the Alternator. Its the drag the Alternator creates that you noticed when the AC is switched on, which will make the engine to bump. Because of the drag from the Alternator, the engine will try harder to drive the dragging Alternator, thereby making the ECU or carburretor to pump more fuel to maintain the normal engine rpm, hence the thirsty running.

But when you are doing about 100km/h or so, the power the engine develops at that point is enough drive the Alternator effortlessly, depending on how sound the engine is or how good the engine managenent is. That is to say, it will consume less than leaving you windows open at such speed.

Its the Alternator that powers the engine once its running, not the battery, hence, the cut out function. Thats why battery can be disconnected while engine is running and still will be running. It will only draw power from the battery if your Alternator is faulty, failing or a broken engine Auxilliary/Alternator belt.

Even headlight, car stereo, leaving unnecessary electronics on while engine is running makes the Alternator to increase drag and makes the engine to consume extra unnecessary fuel. If your Alternator is faulty or not designed to carry capacity of a particular Compressor, your battery will always be running down or will even kill the battery sooner than you expect.

Ikenna
Re: How Does The Use Of Car AC Affect Fuel Consumption? by Siena(m): 11:37pm On Dec 21, 2012
^^^ Not strictly true, Ikenna. Sure, any load on the alternator will be transferred to the crank, which has an adverse effect on gas mileage, and engine output.

However, the lesser aircon loads transferred to the crank when operational, are from the condenser fan and blower motor. These loads greatest when the aircon is first switched on (moment of inertia).

The greatest loads come from the compressor's electro-magnetic clutch (if it has one). This is a coil, and is energised as long as the aircon is operational. No moment of inertia here.

The heaviest load comes from the compressor displacement itself. This is purely mechanical, and has nothing to do with electrics. The compressor runs pistons, arranged pretty much like a Rotary engine (though Rotary engines employ Rotors). When the aircon is swiitched on, and the magnetic clutch is engaged, the pistons begin to displace gas. This load is greater than that of the condenser fan, blower motor and electro-magnetic clutch combined, and has the greatest impact on engine load, and gas mileage.

Any pump that has to displace air, gas or fluid WILL work hardest during displacement. A mechanical power steering pump has no electrical parts, but will cause engine drag and worse gas mileage. Turn the steering full lock, and observe engine rpm drop, before the idle control kicks in, and raises the rpm threshold.

A better comparison has been inardvently created by Nigerian vulcanizers. Lots of them use aircon compressors driven by either an A/C motor, or a petrol one. The aircon compressor electro-magnetic clutch plate is welded to the belt pulley, so it's driven constantly, as long as the pulley is driven. The motor runs as fast as its governed speed permits - as long as the air line / gauge is NOT connected to a tyre valve. As soon as it's connected to a tyre valve, you'll notice the speed of the drive motor (petrol or A/C electric) drops. Unlike an automobile engine, there's no idle control to raise the rpm, so it stays low, until the line is removed from the receiving tyre.

There are several examples that can be sited, an outboard motor on a boat is a pump, the moment the propeller is in the water. Run the engine, then raise the propeller from the water, and the speed will increase (unloaded) to the point the motor would actually destroy itself.


Automobile manufacturer's are striving to reduce the effects of aircon on gas mileage. They have done this by getting rid of the compressor's electro-magnetic clutch, the greatest single alternator load from the aircon system. So aircon compressors are split into two types:

* Positive displacement (older systems with electro-magnetic clutch).
* Variable displacement (newer systems without electro-magnetic clutch).


The newer system is much better on gas mileage - my 2008 BMW 120d M-Sport has the newer clutchless system, and switching on the aircon does NOT cause a drop in engine rpm. My 2002 Audi S8 Quattro has the older clutch-based system. The clutchless compressor is fitted to current Audi, VW, Mercedes-Benz, Peugeot, Toyota, Nissan, Honda. In fact, most automobile built after 2010 will have the clutchless system, though it was first introduced around the year 2000.
Re: How Does The Use Of Car AC Affect Fuel Consumption? by wisesystem: 3:28pm On Dec 24, 2012
true talk
Re: How Does The Use Of Car AC Affect Fuel Consumption? by Euroclydon(m): 7:44pm On Dec 25, 2012
Siena: ^^^ Not strictly true, Ikenna. Sure, any load on the alternator will be transferred to the crank, which has an adverse effect on gas mileage, and engine output.

However, the lesser aircon loads transferred to the crank when operational, are from the condenser fan and blower motor. These loads greatest when the aircon is first switched on (moment of inertia).

The greatest loads come from the compressor's electro-magnetic clutch (if it has one). This is a coil, and is energised as long as the aircon is operational. No moment of inertia here.

The heaviest load comes from the compressor displacement itself. This is purely mechanical, and has nothing to do with electrics. The compressor runs pistons, arranged pretty much like a Rotary engine (though Rotary engines employ Rotors). When the aircon is swiitched on, and the magnetic clutch is engaged, the pistons begin to displace gas. This load is greater than that of the condenser fan, blower motor and electro-magnetic clutch combined, and has the greatest impact on engine load, and gas mileage.

Any pump that has to displace air, gas or fluid WILL work hardest during displacement. A mechanical power steering pump has no electrical parts, but will cause engine drag and worse gas mileage. Turn the steering full lock, and observe engine rpm drop, before the idle control kicks in, and raises the rpm threshold.

A better comparison has been inardvently created by Nigerian vulcanizers. Lots of them use aircon compressors driven by either an A/C motor, or a petrol one. The aircon compressor electro-magnetic clutch plate is welded to the belt pulley, so it's driven constantly, as long as the pulley is driven. The motor runs as fast as its governed speed permits - as long as the air line / gauge is NOT connected to a tyre valve. As soon as it's connected to a tyre valve, you'll notice the speed of the drive motor (petrol or A/C electric) drops. Unlike an automobile engine, there's no idle control to raise the rpm, so it stays low, until the line is removed from the receiving tyre.

There are several examples that can be sited, an outboard motor on a boat is a pump, the moment the propeller is in the water. Run the engine, then raise the propeller from the water, and the speed will increase (unloaded) to the point the motor would actually destroy itself.


Automobile manufacturer's are striving to reduce the effects of aircon on gas mileage. They have done this by getting rid of the compressor's electro-magnetic clutch, the greatest single alternator load from the aircon system. So aircon compressors are split into two types:

* Positive displacement (older systems with electro-magnetic clutch).
* Variable displacement (newer systems without electro-magnetic clutch).


The newer system is much better on gas mileage - my 2008 BMW 120d M-Sport has the newer clutchless system, and switching on the aircon does NOT cause a drop in engine rpm. My 2002 Audi S8 Quattro has the older clutch-based system. The clutchless compressor is fitted to current Audi, VW, Mercedes-Benz, Peugeot, Toyota, Nissan, Honda. In fact, most automobile built after 2010 will have the clutchless system, though it was first introduced around the year 2000.



Me i dont understand all the grammer Siena is dishing out... Please speak clear english, AC dey consume fuel or not? all dis differential matters does not register wit a typical Naija man like me...no vex.
Re: How Does The Use Of Car AC Affect Fuel Consumption? by Euroclydon(m): 7:44pm On Dec 25, 2012
Air Conditioner Fuel Consumption

AC vent
In early cars like the 70s Peugeot 504 and other cars before that era when car AC compressors were bulky and not very efficient, it is indisputable that using your car Air Conditioner while driving while driving means parting with some extra liters of fuel. But we are in an era when car compressors are better built and lighter. That doesn't mean they don’t require power from the engine to be driven as is most noticeable at low rpm like when the car is idling and you switch on the AC. The noticeable drop in rpm is mostly due to inertia.

So, your glasses are down and your AC is off so you can save fuel. I bet the only place you are going to save that fuel in today’s cars is ‘in your head, not in your fuel tank’. If your glasses are down and you are driving at speeds in excess of 80km/h (about 55mph), the inside of your car will be working like a big balloon or parachute to pull your car back as air flows in through the windows. This way, the engine will be working harder than it should to keep the car moving at this speed. The car is at its best aerodynamic form when the glasses are up, making it glide effortlessly through the air.

air flow around a car
Your must have noticed that you seem to drive a little faster when your glasses are up. That is not just because you are sealed from exterior noise made by the wind as it slaps against the hood (burnet), windshield, and side mirrors, but also because the engine finds it much easier to push the car through the gears to a higher speed.

What if you are sitting in high traffic where you can’t drive fast to experience drag. You will save some fuel in this condition if you don’t use your AC. You can turn off your engine altogether so you don’t use any fuel at all. And if you are lucky to be driving one of these new cars equipped with cylinder deactivation technology , you don’t need to bother as your car will do just that for you.


But we are talking of sitting in traffic here. Would you rather sit in traffic with your glasses down, inhaling gas fumes from other peoples exhaust pipes and listening to people cursing? No! I suggest you wind those glasses up, hit that climate control button and hit play on your stereo. That way, you will pass the time quick and go home refreshed, instead of saving money in traffic to spend it on aspirin.
Read more on Car AC fuel consumption





http://101carsense.blogspot.com/2012/12/air-conditioner-fuel-consumption.html



this has said it all simply.
Re: How Does The Use Of Car AC Affect Fuel Consumption? by Siena(m): 8:24pm On Dec 25, 2012
Euroclydon: Me i dont understand all the grammer Siena is dishing out... Please speak clear english, AC dey consume fuel or not? all dis differential matters does not register wit a typical Naija man like me...no vex.

Bro, I don't get you.

The thread title's pretty clear to me - "How Does The Use Of Car AC Affect Fuel Consumption?" Which to my sluggish brain means he's aware the use of aircon does affect gas mileage, what he's not sure of is "How"? If the OP simply wanted to know if the use of aircon affected gas mileage, the title would have been - "Does The Use Of Aircon Affect Gas Mileage?" Then the answer would have been a simple yes or no.

The blog you've linked to is pretty much the same. I don't understand it when you guys say "big grammar" etc. The only reason you won't follow is because you feel it's too long to read, and after the first few lines, you give up. My niece is 13, and she understands my write-ups. If there are aspects she gets stuck on, she'll either ask me to clarify, or she'll Google for herself. That's how people learn.

I'm not a computer Nerd, and there are lots of write-ups in the Programming section I don't understand, but still, I read the lot, and Google the grey areas, combine them with the aspects of the original write-ups that did make sense to me. And end up with a clear picture. I don't wait to be spoon-fed, it's just not my style.

Knowledge doesn't drop upon us, we go out there, and grasp it with both hands. There's no other way to learn, unless we simply refuse to do so.

Merry Christmas.

2 Likes

Re: How Does The Use Of Car AC Affect Fuel Consumption? by Euroclydon(m): 9:02pm On Dec 25, 2012
Siena:

Bro, I don't get you.

The thread title's pretty clear to me - "How Does The Use Of Car AC Affect Fuel Consumption?" Which to my sluggish brain means he's aware the use of aircon does affect gas mileage, what he's not sure of is "How"? If the OP simply wanted to know if the use of aircon affected gas mileage, the title would have been - "Does The Use Of Aircon Affect Gas Mileage?" Then the answer would have been a simple yes or no.

The blog you've linked to is pretty much the same. I don't understand it when you guys say "big grammar" etc. The only reason you won't follow is because you feel it's too long to read, and after the first few lines, you give up. My niece is 13, and she understands my write-ups. If there are aspects she gets stuck on, she'll either ask me to clarify, or she'll Google for herself. That's how people learn.






I'm not a computer Nerd, and there are lots of write-ups in the Programming section I don't understand, but still, I read the lot, and Google the grey areas, combine them with the aspects of the original write-ups that did make sense to me. And end up with a clear picture. I don't wait to be spoon-fed, it's just not my style.

Knowledge doesn't drop upon us, we go out there, and grasp it with both hands. There's no other way to learn, unless we simply refuse to do so.

Merry Christmas.



bros no vex...did not mean to aggravate you like dis. I was even expecting you to ignore me. MERRY XMAS BRO!

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