Does A/C affect mileage?

I've had people tell me that using the A/C cuts down on gas mileage, I am not sure if this is true or not since my mpg readings are always different with each tank. Not starting another mileage complaint thread, I drive a truck and really don't give a damn about getting good mileage! Just trying to figure out if this is true or not, thanks!

 

MythBusters confirmed this as a yes, though not very noticeably in most cases.

 

Maybe a little but running A/C is def better than driving with the windows down

 

I think the mythbusters did a show on this, you should check out youtube for the results! If i remember correctly it was AC on vs windows down.

 

Yes, it does affect your MPGs. The AC unit puts an additional load on the engine, when it is on.

 

I think they said that under 45MPH windows down was better, above that AC was the way to go... If it's nice out, I always prefer windows down, but I am not concerned with that 0.5MPG

 

http://brokensecrets.com/2010/08/10/air-conditioning-affects-gas-mileage/

 

Start truck, stare at tac, flip AC on and off. It will affect it, a little

 

Doubt it's a significant amount.

 

hmm, I have a question for all you guys regarding the AC as well. I didn't want to start a thread either.


Is it just me, or is there a slight decrease in acceleration with the AC on? I've always felt like the truck is a bit sluggish on take off with the AC on, I just can't tell if I'm imagining.

 

Of course it affects the performance of the engine. The A/C compressor is another pulley along the serpentine belt that draws power from turning rotation of the motor, any load put on it will cause in a direct decrease in output power. Which is why you never run the A/C if the car is overheating and why it blows warm air when the car is off.

My dad's old Mini Cooper would barely make it up the hill to our house if his A/C was on.

 

Ah, cool! Thanks for the explanation, and the advice.

 

Using a carefully calibrated Scangauge 2 driving computer (accurately calibrated over a 2 year period) on a flat 4 lane highway (that I travel every day at the same speed +/- 1mph), the AC makes the MPG go down from 21.5mpg to 19.5 (+/- .4mpg) at 55mph. Turning off AC & opening windows decreases to 19.2 (+/- .6mpg). These are averages of 3 runs over 4 miles of road, resetting computer at same place in road each run.
I wasted some gas & time with this experiment, but I just wanted the facts. Often there are only feelings & unsubstantiated opinions on performance issues in this forum.
Would love it if someone else would duplicate this with their truck.
I am trying to increase low end torque & premature downshifting for towing a heavy trailer thru the Rockies this summer. Any ideas?

 

Your approach is the only way to get numbers in the ballpark. Thanks for posting. I have been watching my Scangauge and estimated 1.0 to 1.5 mpg loss, but I have not done anything as systematic. I tow for months out of the year in the western states and I operate the AC manually. I turn it on for the downgrades, and off for the upgrades. Doing that eliminates the extra mileage loss and the drag on the engine. You can do it for very slight grades too. I have long wished someone would design a circuit to do this automatically. While the inside temp varies a bit, I can generally keep it cool by doing this.

 

It would be interesting to see the difference under 45 MPH. Most data I have seen has said that under 45 MPH, MPG drops less with windows down than with AC on, and that over 45 MPH windows down hurts more than AC on does.

Of course there are a lot of variables... DblCab versus Regular or Access Cab, all windows down versus only two, if the sliding rear glass is open...

 

Yes it has to reduce it a little by the laws of physics (law conservation of energy). Also a little for the power steering, pwr brakes, keeping the battery charged and running headlights, radio, fans or any other accessories.

But not nearly as much as many people think. The amount of energy from the fuel that goes into powering the drive train is very big compared to that used for powering the other systems.

Plus a lot of the fuel energy is wasted producing useless heat and overcoming friction in all systems.

 

Props to you for a decent test w/some numbers!