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using air conditioning= less power and mpg

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Old 05-19-2005, 07:21 PM   #1
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using air conditioning= less power and mpg

is this true? ive heard different people say different things.
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Old 05-19-2005, 07:28 PM   #2
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Yes, it's true.
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Old 05-19-2005, 07:32 PM   #3
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It was busted on Mythbusters as far as MPG.
Open window drag vs. A/C

Last edited by 4-RUNNIN' FREAK; 05-19-2005 at 07:34 PM.
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Old 05-19-2005, 07:39 PM   #4
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i think i saw that episode awhile ago but i couldnt remember what outcome of it. has anyone ever removed all their a/c components?
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Old 05-19-2005, 07:45 PM   #5
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It was Episode 22: Boom-Lift Catapult.

I was lookign it up for some worthwhile info to post, and it was actually on last night (18th).


Episode 22: Boom-Lift Catapult
Buster lends a hand as the MythBusters explore the myth of the boom-lift catapult. Will Buster overcome the raw power of a 30,000-pound piece of machinery, or will the boom-lift turn into the ultimate medieval catapult? Then, worried about the price of gas? Tune in to Jamie and Adam's investigation into the most fuel-efficient way to keep cool in the car: turning on the air conditioning or opening the windows.
premiere: Nov. 10, 2004
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Old 05-19-2005, 07:45 PM   #6
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Yes. I removed all my AC components on my 95 Civic SI. All it really did is save 40lbs since I was running with the belt off anyway. Stupid move on my part. Remember, you have to de-pressurize the system.

My rig is significantly slower with the AC compressor running. I never saw that mythbusters episode, but I can tell you right now that my mileage goes down if I try and maintain the same speeds and driving style as when I don't need AC. I track my mileage on Excel charts and the mileage drops a bit for both our cars during the summer.
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Old 05-19-2005, 07:49 PM   #7
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Significantly slower? Something isn't right. I can't tell on or off, as with most other premium V6+ vehicles.
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Old 05-19-2005, 07:56 PM   #8
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Originally Posted by 4RUNR
Significantly slower? Something isn't right. I can't tell on or off, as with most other premium V6+ vehicles.
Absolutely. Here is an example: AC on full blast, half-throttle, merging on the freeway (especially uphill) to 65MPH. If I kick the AC button off while holding the pedal in the same position, acceleration increases and I can back off the pedal a bit.

Unfortunately I get to test the AC a lot here, unlike the North Pole folks.

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Old 05-19-2005, 08:00 PM   #9
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I notice no difference at all with it on or off on my 3.0.
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Old 05-19-2005, 08:06 PM   #10
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My girlfriends 87 Corolla was getting a smog check yesterday,we're having problems keeping the idle down (only off a tiny bit), the guy turned on her headlights and the idle went down around 80 rpm

When I turn on the A/C I feel a drag on my 22re.
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Old 05-19-2005, 10:33 PM   #11
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Yup, definitely uses more gas and nets you less mpg. Think about it, the motor has to run an extra accessory driven off a belt. Of course you will use more energy than if it weren't there.
Now running AC vs leaving the windows all the way down is more tricky, but I suspect in most cases that if you are going fast enough, the AC will be more efficient.
As for being able to feel the drag on the motor, in my experience, you can tell the difference. I had a compressor sieze once and it stalled the engine flat out.

J.
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Old 05-19-2005, 10:38 PM   #12
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How much horsepower, on average, do you think you guys lose by turning on A/C? (i.e. how much does it take to turn the belt for the A/C compressor?). Are there any electric systems to run an A/C compressor? Or would the power needs be too great hence why they run it off of a belt on the engine?
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Old 05-19-2005, 11:04 PM   #13
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hmmmm...good question, we could probably do a search on the web and get an answer. Only problem would be, the answer varies depending on how much work you need the compressor to do. If it's humid and hot, it would really be working. Plus size of the compressor, etc....

I think it would be too difficult to run it off an electric motor, else the car manufacutrers would have done it already and bumped up their corporate gas mileage numbers. I would guess that the alternator's need to make that much power would require the engine to work too hard to make it an efficient process. My 2cents anyway.

J
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Old 05-20-2005, 12:01 AM   #14
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Quote:
Originally Posted by CoedNaked
How much horsepower, on average, do you think you guys lose by turning on A/C? (i.e. how much does it take to turn the belt for the A/C compressor?). Are there any electric systems to run an A/C compressor? Or would the power needs be too great hence why they run it off of a belt on the engine?
Can't speak for its horsepower requirements, but I think it does take up a fair amount of power. On older vehicles without serpentine belts, the A/C belt would always be bigger than the alternator belt.
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Old 05-20-2005, 12:51 AM   #15
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Quote:
Originally Posted by 4-RUNNIN' FREAK
It was Episode 22: Boom-Lift Catapult.

I was lookign it up for some worthwhile info to post, and it was actually on last night (18th).


Episode 22: Boom-Lift Catapult
Buster lends a hand as the MythBusters explore the myth of the boom-lift catapult. Will Buster overcome the raw power of a 30,000-pound piece of machinery, or will the boom-lift turn into the ultimate medieval catapult? Then, worried about the price of gas? Tune in to Jamie and Adam's investigation into the most fuel-efficient way to keep cool in the car: turning on the air conditioning or opening the windows.
premiere: Nov. 10, 2004
What they said was that running the AC does lower your MPG. But driving with all your windows down also lowers it the same amount due to the 'parachute' effect of the air drag.

HOWEVER, in the 4Runner if you roll down the rear window I believe this solves the parachute problem. The air simply flows straight through the car and out the back thus avoiding the blockage that causes drag.

I love my truck
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Old 05-20-2005, 02:12 AM   #16
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On the freeway the AC is fine but in town during slow stop and go traffic your fan clutch will lock up to cool the AC condensor. The fan is what sucks the power out of your engine not so much the AC its self. The toyota fan clutch isnt a speedy device either it will slowly lock up and it will pretty much stay locked until you get up to freeway speeds for a while and the clutch cools off letting the fan unlock.

If you have any doubts just let your truck idle for about 15 mins with the AC at full blast on a warm day. Then lift the hood and watch the fan when you accelerate. It will pull so much air that it actually stretches and offsets on its axis when you rev the motor even a little.
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Old 05-20-2005, 04:59 AM   #17
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I agree with Ganoid. The fan kills my motor MUCH more than the A/C does. When it's locked up taking off, the thing doesn't want to go anywhere!
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Old 05-20-2005, 05:02 AM   #18
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I did some searches on the net regarding AC and HP loss on dyno's. The only real credible source I found was Sport Compact Car, and a dyno test on a Sentra SE-R. What's funny about this, is that the Sentra has a full throttle AC disengage feature that kicks the AC off at WOT. So, they had to manipulate the TPS slightly to allow the car to run WOT with the AC on. Anyway, they realized a 10HP loss; attributing 1-2HP of that loss to their manipulation of the TPS itself. So, on a Sentra SE-R motor, they lost about 9-10WHP out of 180 crank HP. So, the approximate loss is roughly 10% HP with the AC on (on that motor). They made no mention of TQ numbers.

TQ numbers obviously would have to do a lot with how much the AC effects performance too. The difference in our 94 Accord EX with the AC on is much greater than the difference in the 4Runner with the AC on. Both are 5-speeds, so drivetrain HP/TQ loss is similar. The Accord simply does not make as much torque...70 ft-lbs less to be exact; at a much higher RPM. To go anywhere quickly in that thing I have to kick the AC off. Pretty sad.

When I was driving around a 97 4Runner with the supercharger, the AC on was very hard to detect through the seat of my pants dyno. I attribute that to the sheer TQ increase down low - which is amazing (even without the much needed fuel/tuning mods).

So anyway, I don't think the Mythbusters test applies here since they were testing windows down vs. AC on. They need to test AC off vs. AC on in order for us to use their experiment as an argument.

I like to yell "NAAAAAWS!" out the window at ricers when I disengage the AC button while racing them at 150MPH.
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Old 05-20-2005, 07:13 AM   #19
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Quote:
Originally Posted by 4-RUNNIN' FREAK
It was busted on Mythbusters as far as MPG.
Open window drag vs. A/C
That would depend on the vehicle. My dads gets better mileage with the a/c off and the windows down. He drives a 1993 Ford Ranger STX super-cab.

Edit: He does calculate his mileage every time he refills.

Last edited by outcast; 05-20-2005 at 07:14 AM.
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Old 05-20-2005, 07:23 AM   #20
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Originally Posted by hafftrak
Actually, my AC gets used more in the winter than summer. Defrost actually runs the AC compressor to dry the air. 'CFC-linked' I think they call it?
Good point!
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