Why does a car drive slower with a/c on?
08-28-2007, 10:57 AM
#31
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Originally Posted by Slithr,Aug 28 2007, 12:23 PM
One technique I've seen for maximizing mpg with the a/c on is to keep fan speed up, use recirculate and set the temperature down (warmer) a little to keep the compressor from running as much. The compressor will kick in and out as it is needed to maintain the set temperature.
08-28-2007, 10:53 PM
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Originally Posted by Mr.E.G.,Aug 27 2007, 11:38 AM
i just want to take this opportunity to vent about a pet peeve of mine.
first, here's the setup...
yes, it is true that having the ac on will hurt your gas mileage (with the exception of rare cars that use some other means to power the ac compressor.) the reason for this is that the ac compressor pulley is turned by the engine by a belt. the ac compressor has an electric clutch that engages when you turn. so when the ac is not on you get better gas mileage because its just a pulley with little mass. when you turn the ac on and the electronic clutch engages in the ac compressor your engine is now rotating the inside components which have mass which puts more of a load on the engine causing it to get poorer gas mileage. same concept as having heavier wheels or drivetrain components.
the thing thats tricky is that unlike every other drivetrain component the ac compressor can be turned on or off so it confuses some people.
so here's the part that annoys me...
once your ac compressor is turned on the gas mileage sapping begins. its an on or off thing. your ac compressor is either on or off. thats its. the speed that the air comes out of the vents is controlled by an electric fan. i constantly hear people say that to conserve gas they drive with their ac on the low setting. it doesnt work that way. if the ac is on it doesnt matter if it is on low or full blast. again, its just an on or off thing.
first, here's the setup...
yes, it is true that having the ac on will hurt your gas mileage (with the exception of rare cars that use some other means to power the ac compressor.) the reason for this is that the ac compressor pulley is turned by the engine by a belt. the ac compressor has an electric clutch that engages when you turn. so when the ac is not on you get better gas mileage because its just a pulley with little mass. when you turn the ac on and the electronic clutch engages in the ac compressor your engine is now rotating the inside components which have mass which puts more of a load on the engine causing it to get poorer gas mileage. same concept as having heavier wheels or drivetrain components.
the thing thats tricky is that unlike every other drivetrain component the ac compressor can be turned on or off so it confuses some people.
so here's the part that annoys me...
once your ac compressor is turned on the gas mileage sapping begins. its an on or off thing. your ac compressor is either on or off. thats its. the speed that the air comes out of the vents is controlled by an electric fan. i constantly hear people say that to conserve gas they drive with their ac on the low setting. it doesnt work that way. if the ac is on it doesnt matter if it is on low or full blast. again, its just an on or off thing.
08-29-2007, 08:43 AM
#34
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Originally Posted by wanabe,Aug 27 2007, 06:37 PM
(the top is that thing under that black plastic thing behind the seats- it is optional... and some of us have never used it- going on 8 years and i havent seen mine yet!)
Tan
08-29-2007, 12:54 PM
#37
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Most cars cycle the compressor on and off depending on load which is based one inside/outside temperature, humidity, and vehicle speed. If it did not cycle off, the pressure would build up too high and blow a hose or seal.
09-01-2007, 09:52 AM
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Originally Posted by fusionchickenleg,Aug 30 2007, 11:37 AM
yea it really sucks...my Evo in hot weather with a/c on drives like dog shit....sometimes i feel like pulling my shifter out and throwing it at my windshield.
I really wish other manufacturers wouldpony up for the independent AC systems other manufacturers like GM and Nissan have. My brother's 04 XTerra has one and man is it great to turn on AC without the requisite loss of power. One of the best auto inventions ever.
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