How does running A/C affect your MPG's?

[tpollauf]

OK. So I did a scientific study the other day and was a bit surprised on how much running the A/C robs you of MPG's. This is with the 2.4l engine and 5-speed manual tranny. Here's my numbers based on my scaqngaugeII. Oregon to Swanton (80% hwy) 35 mile distance. Outdoor air temp = 93'f. A/C = on, 55-60mph. Got 34mpg. After leaving this graduation party in Swanton Ohio, headed to lake Erie in Port Clinton (100% hwy on Ohio turnpike) 55 mile distance and got 42.3mpg NO A/C and went an honest 55mph the entire time. Now my ScangaugeII historically has been 3-4mpg HIGHER than actual mpg numbers. This means when factoring in the other variables my numbers reflect this: AC on = 32-34mpg @55mph. A/C off = 38mpg @ 55mph. This equates to 10% - 15% fuel efficiency loss by simply running the A/C.

Just curious if others share the same numbers. Also for you 1.8l Vibe owners have even worse numbers seeing that the smaller engine would have more of a load on it with A/C on.

[Old Tele man]

...yep, 10-15% drop in FE is the same as I got with my 2009 1.8L Vibe with 4-speed automatic here in Arizona when I was driving back-n-forth to work (26 miles each way); also, measured using a ScanGauge-IIâ„¢.

[vibenvy]

I definitely won't be running the AC on the way to and from Erie. Then again, I never use the AC unless my grandma is with me anyway.

[ColonelPanic]

measured using a ScanGauge-IIâ„¢.

Love the ScanGauge... I have the ScanGauge-E in my Accent, I need to get another for the Vibe.

It's neat toggling the A/C off then seeing the instantaneous FE readout on the SG go up.. I usually gain a couple MPG with it off. Obviously, in addition to A/C I also see a noticeable hit during periods of heavy electrical loads (lights, fan, and the rear defrost/heated mirrors.)

[jkm311]

I always turn off my A/C whenever needing to hit the accelerator, usually just merging on the highway. I don't turn it back on until I am able to settle into O/D comfortably. I just can't justify the extra stress on the engine/belt for only 30 seconds of discomfort. Anybody else do this?

[trb]

I always turn off my A/C whenever needing to hit the accelerator, usually just merging on the highway. I don't turn it back on until I am able to settle into O/D comfortably. I just can't justify the extra stress on the engine/belt for only 30 seconds of discomfort. Anybody else do this?

I only run the AC whenever I need it, manually cycling it on for a minute, then off for 3-4 minutes whenever I can. Kinda hard to keep it off for long in the Houston heat though.

[j42.snyder]

10-15% seems about right from my findings. When mine does get used, it's typically been on my drive home from work - virtually never in the morning going in. On tanks when I've used it daily for the trip home, I see about a 5-7% drop compared to average (technically I measure an increase in consumption). I don't have any electronic feedback - just ongong measurements for each tank. Consistent fills are difficult - but long term averages are accurate. I only have a vacuum gage in the car for feedback.

This is why I modified my controls so that it no longer forces the A/C on with defog. That way I can keep warm air on the glass whenever needed without the fuel consumption penalty. If I really need the A/C to help it out, it's just the push of a button away...

John

[KITT222]

I've modified my defog too, so it doesn't go on with the AC. Good thing, too, since the defog spreads heat a lot better than just the vents. I hardly ever use AC. I can only justify it if it's 95F, and hotter. I either deal with the heat, or open my windows. That's why I carry around my trusty sunshade. It helps,a long with my vent visors. I NEEDED the visors last summer, where I'd park my Vibe for eight+ hours at work. But when I have the AC on, I turn it off for accelerating, or passing someone. Last Thursday I drove my family to dinner for my sister's birthday, and I used the AC (it was roughly 93F). We were in traffic a lot, so it really didn't make too much of a difference. On the way back we had the windows down (cooled to 87F). One interesting thing I have, though, is a Celsius thermometer with a probe on my mirror outside, and the screen has an internal thermometer, so I get to see the difference in temperature outside and inside with the black interior.

But what I really need is a day with a three-digit heat index, so I can spend some time outdoors, working on something, so the heat won't bother me again. Last summer we had two days in a row with 130F heat index, and we were working at the amusement park on the blacktop without shade. After that heat really wasn't a bother.

[jake75]

I don't know - when I go out to eat I usually order a premium draft that costs me $5-6, so why not also splurge on a/c when necessary.
Same attitude at home - when it gets hot, the a/c goes on. That said, I spend some time in my a/c home to clip out those grocery coupons that come with the Sunday paper.
I justify all my bad spending habits via the fact that I save money by not playing golf, fishing, or hunting.

[beemerphile1]

I don't know - when I go out to eat I usually order a premium draft that costs me $5-6, so why not also splurge on a/c when necessary...

My thoughts also. I don't know how much AC affects fuel usage but I don't care too much either.

You can save fuel by staying home and not driving.
You can save fuel by suffering and not using AC.
I see them as about the same logic.

[star_deceiver]

My A/C doesn't affect my MPG's at all....

[Mark]

I don't think it matters all that much, and over 45 mph the A/C has less impact than the drag introduce by driving with the windows down. I used to drive from Cheyenne to Denver (120 m each way) a couple times a month with the A/C on and the cruise set at 80 and still got 35+ mpg. At this elevation the sun's intensity can make it very uncomfortable in a closed vehicle, even when the temp is in the low 70s. I don't see any point in being uncomfortably hot for the sake of maybe saving a little gas, the car came with A/C for a reason.