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Discussion Starter · #1 ·
It's finally cooled off enough so I don't have to run the A/C 100% of the time. I've noticed I am averaging 6-7mpg better when not using A/C at all. Almost all other cars I've driven including other small 4-cyl'ers I've only noticed about 2mpg at most difference. Have others compared with and without A/C?
 

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I have done this. Not in my around town driving, but on the freeway. With A/C on the freeway, I get 26-28mpg. Without A/C on the freeway, I get 30mpg. I'm sure around town in slower traffic it woudl make even more of a difference.
 

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The air conditioner compressor pulls a certain amount of HP from the engine. You can usually hear the change when it engages. Our SXTs got miserable mileage this summer, air on all the time. Funny thing though, my Magnum RT didn't even notice when the air was on, must be the few HP drawn by the compressor was minimal compared to the 350 HP available. Mileage never varied.
 

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Discussion Starter · #5 ·
BlueHawaii said:
something wrong eh? my a/c kills off 5 mpg and isn't very cold to begin with, what's up with that.
Push the Recirculation button. Your A/C will then get ice cold.
 

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6-7 mpg with A/C off?? Somethin ain't right! 5% delta maybe, BUT 20%??

When you say 6-7 diff, are the driving conditions of the 2 situations EXACTLY the same? The only real way to do a controlled experiment would be in a lab setting, as there are so many variables day to day, season to season, that a road test would not be scientifically conclusive.

Don't forget, with the defrost on, and ambient temp above -10C, the compressor will also engage.

S
 

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Had the same problem with my SXT, i dont do a lot of city driving, but on the hwy with my AC off i usually get about 575 km to a tank, and with it on, i get just over 500, so needless to say, i try not to use it a lot on long road trips
 

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So far we have averaged 26 mpg in the AWD all summer, the A/C on most of the time. Just recently last two tanks no A/C was used but the defroster was and of course the mileage still at 26. Pretty soon I may stop calculating it because it is just too consistent, and at over 10,000 miles it probably won't change.

The defroster will be in use this fall/winter/spring as much as the A/C was used, so I doubt much will change. She turns it on and leaves it on for the entire ride, even though the windows were clear after 5-10 mins. My wife also drives almost the exact same route every day.
 

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OrangeRT said:
She turns it on and leaves it on for the entire ride, even though the windows were clear after 5-10 mins. My wife also drives almost the exact same route every day.
I hate that. I'd rather drive with the windows down if it's under 90 degrees and above 60 outside, but can't when I'm with the wife. As for the defrost, kick it over to heater after the windows are good and clear. The heater doesn't use the A/C compressor.
 

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Ditto HSKR.... it drives me insane to get back into the car and see the AC left on. She always complains when I drive around in summer with windows down, sunroof open, AC- OFF.

Aaron
 

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I know little bit about aircon as I've got extensive project work on cooling subzero temps with computers like minus -82C.
But the principles are the same. The aircon has a cycle period it switches on and off as temperatures reach optimal, this means not every car has the same amount of refrigerant in the compressor that condenses the gases in the system. As the compressor kicks in it draws it power from the alternator like most component that uses a lot of electricity. This will equate to about 5% or even 5BHP drop you will notice the idle speeds dropping a tad if switched on.
Coming back to my point why some of you have more of a drop in fuel consumption is that if there is a loss of power your right foot will compensate for the loss in power hence hills and the like doing 30mph will use more fuel to get to the same speeds.
If someone here is getting like a 20% drop in MPG then get your dealer to check the gases in the aircon as you might have a compressor working harder for longer to get lower cabin temperatures. Alternatively you know it’s faulty if it doesn't cool down fast or feels not cool enough?
By the way if you don't use your Aircon at least once every two weeks the compressor will stagnate and can cause premature failure in the aircon system. Call it servicing itself once you press the button for five minutes every two weeks especially during winter times!
I’m not saying your aircon system will be permantely damaged if you don’t do this but it helps to keep the system clean and working better!
 

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We have electric A/C compressors???? I have failed in my man duty to completely examine every inch of the engine bay as of yet. But i was always assuming it was a traditional belt driven unit. Even so parasitic draw will be more obvious on the smaller displacement engines making less power.
 

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If you use your defrost during the winter, no need for the 5 minute A/C workout since the defrost uses the A/C compressor to dehydrate the air. And out A/C comressors are belt driven just like almost every other automotive A/C compressor.
 

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The only thing electrical about the compressor is the clutch mechanism
and I have owned so many airconditioned cars I have lost count,never ever
had a compressor failure and never ever turned air on in winter.
As stated before when you use defrost cycle it uses compressor so no need
for button pushing exercise.
 

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yeah thats why i assumed it was belt driven. We are a ways away still from all electrical accessorys although they are heading that direction.
 

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The pully still pulls power away from the car?
This came from Dodge for the caliber.
If you drive at 40mph all the turn on the A/C then drive at 30mph see if your gas stays the same meaning your not accelarating more to get the same speeds when it draws power form the drivetrain.
 

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bigtsr said:
The only thing electrical about the compressor is the clutch mechanism
Actually, the Caliber doesn't even have an A/C clutch -- the compressor is ALWAYS turning. As clipperjay posted, the ECU controls the displacement of the AC compressor, so normally, it's just set to "0" displacement and as AC requirements increase, the ECU cranks in some displacement using a PWM signal. This also means that the ECU has better control of the AC so it never truly cycles from "on" to "off" but always is somewhere in between. This is probably why is takes some time for the caliber to get cool (?) ECU has to ramp up from "off" to "on" instead of just dumping the clutch...

clipperjay said:
If you drive at 40mph all the turn on the A/C then drive at 30mph see if your gas stays the same meaning your not accelarating more to get the same speeds when it draws power form the drivetrain.
Except that the ETC system will automatically open the throttle a bit more to compensate for the A/C, so if you hold your foot constant, it should stay at the same speed.....
 

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Over here in the UK there are not many days when you really need A/C but I was always told to have it on all the time as otherwise the seals can crack and you lose coolant.

Its cheaper to use the fuel rather than mend your A/C system.
 
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