To air condition or die?


I know it is not helpful to the environment or your wallet to use your air conditioner, but, at least in Kansas, I assure you you will die if you don’t. So… does it use more gas to drive with the windows down or cruise with the windows up and the air on? How does the moon roof factor in?


You need to quit worrying about the environmental boogie man. I promise, he’s not going to eat you and he’s not under the hood of your car.

In 90% of the cases these days, you will use less fuel with the windows up and ac on.



Consumer reports did some elaborate tests, and on average you lose 1 mpg at highway speed by turning on the A/C. In the past with very inefficient compressors, the loss was as much as 4 mpg.

So, relax, be more productive and happy motoring!


What did people in cars do 30-40 years ago…30 years ago…less then 20% of all cars sold had AC…40 years ago…about 1%.


Air compressors on modern cars are lighter, more efficient, and don’t require a lot of power to turn. The air compressors used decades ago (such as the old GM A6 compressor which took a lot of power just to rotate it at all). There’s a slight drop-off in mileage on newer cars but it’s really not enough to worry about and often is not even noticeable.

Mike is correct about A/C use. I got out of high school in 1969 and even then A/Cs were not the norm. Funny thing is that A/Cs were seldom even thought about and few people cared other than the luxury car segment of the population.
(And I’ve lived in OK for many decades so I understand the heat, and especially the 80% humidity part of this)
Mike probably remembers places like Sears, Montgomery Wards, etc. selling add-on A/C units for 150 bucks installed, or something like that.


I’d use the A/C especially if you’re doing more higher speed driving. For city (stop and go) type of driving you will see some effect to mileage but it will be minimal and you’ll be comfortable at the end of the day.

Car and driver did a neat test about gas mileage with a BMW 3 series about one year ago. They did things like under-inflate the tires (this lowered economy by 20%), drive on the highway with the windows down (this lowered mileage by 10% or so), drive in low gear instead of the highest gear (mileage dropped like 25%), and drove with the A/C on (effect on mileage was maybe about 1mpg less).

The bottom line was that for the best economy one should have properly inflated tires, drive in the highest gear possible, keep speed under 60mph, and use the A/C on the freeway.


They had vent windows, air doors under the dash to let air cool your feet, etc. The vent windows broke up the air blast when you lowered the side windows. This worked in most climates, but had little effect in the South.

In July of 1964 I drove a 1963 Buick Riviera with no A/C from Detroit to San Francisco for a West Coast purchaser. The trip went across the Bonneville Salt Flats, a trip I’ll never do again in a non/AC car. The rest of the trip was fun although I averaged only 12mpg. Reno was till fun and affordable then.

A/C is probably the greatest invention since the self starter and even econo-cars with 800 cc engines in Asia have Air.


hey had vent windows, air doors under the dash to let air cool your feet, etc. The vent windows broke up the air blast when you lowered the side windows. This worked in most climates, but had little effect in the South.

I only owed ONE car without AC that had vent windows. My car today has air doors under the dash to cool my feet…and yes I have AC.


Mike probably remembers places like Sears, Montgomery Wards, etc. selling add-on A/C units for 150 bucks installed, or something like that.

Yup…And I couldn’t afford it back then. My first vehicle with AC was my 90 pathfinder. Installed at the Dealer when I bought it.


There have been quite a few studies done on this subject, including Myth Busters and those mentioned above. Everything that I have seen or read says that you MIGHT lose about 1% fuel efficiency. Proper tire inflation, properly-operating A.C. system, feather foot on the gas pedal are a few of the keys to getting the best economy out of your vehicle. One study looked at it from this standpoint. Would you rather be comfortable going to, and getting to your destination, or show up all pi$$ed off, grumpy, and be generally a P.I.T.A. to save 1% or less in fuel mileage? That question by itself convinced me that I’d rather show up with a nice smile and a bubbly personality, especially if I’m going to see a potential customer to do handy work for. N.H. summers were a (female dog) without air, except on the Harley, of course. Any hot/humid place is a dog without air. Now that Freon R-12 is no longer used, how is air conditioning (or refrigeration of any kind) bad for the environment?
You might also want to consider road rage as a factor in determining whether or not to use your A.C. If not you personally, just think of the poor slob next to you on the Interstate that might not have ‘air’. Maybe he/she needs to go over 70 mph just to make it bearable through those hot, humid places and gets p.o.'d at you because you’re only going 55-60 m.p.h. while using your ‘air’ and being as fuel efficient as you can be at highway speeds. Even in the Colorado mountains/front range flat lands, I use ‘air’ when necessary. Yeah. Yeah. “It’s cold–but it’s a dry cold”. “It’s hot–but it’s a dry heat”. I don’t care. It’s STILL freaking COLD or HOT! (Tongue in cheek, of course).


Those neat vent weindows were gradually phased out in the 60s. My '65 Dodge Dart’still had them, my 66 Chevelle Malibu had them but they were gone from my 76 Ford. Once the majority of cars had air, it was a cost saving to get rid of the vent windows. The neatest car was the 63 Mercury; it had vent windows and a reverse slant rear window that lowered elec- trically, providing good flow through ventilation.


I’ve had air since 1976 and have enjoyed our holidays trips much more! The last trip we took without air was in 1975, a 7000 mile trip through Canada and the Western US. After several heat migraines, I decided that was it for non A/C travel. If I had to chose between wheels and A/C on a car, it would be a difficult choice.


had them but they were gone from my 76 Ford

And by 76 less then 20% had AC.

My 73 and 74 Vega didn’t have them…My 69 Firebird didn’t have them…


I work in SE Turkey, near Diyarbakir, between July and September. Temperatures approached 120F in the peak of the day. I did not see one car there that had A/C unless it was a government car. I am not telling you that the A/C should not be used, but don’t say that you will die without it.

Use whatever you are comfortable with, the decrease in MPGs is negligible either way you like.


The definitive answer: It depends- on the car and speed, mainly. It’s usually close to a wash between using the a/c and rolling down the windows at highway speeds.

If there is an interior shade for the moonroof, use it to reduce solar gain and glare.


Be cool and be happy. It will cost you little or nothing to run that A/C In the old days they cost a lot more, but fuel was cheap and few people worried about clean air. Things a lot different today, opening the windows will often cost more fuel. Drop your highway speed down a mph or two and that will likely more than make up any loss do to A/C


I miss vent windows on pickups. They were handy boogers, especially if you messed up and locked your keys up in the truck. The last vent window I had was an 94 F150. I haven’t seen air doors under the dash since a 78 Chevy C10.



I’ve heard supposedly that the notion of getting better mileage with AC as opposed to windows originated as a marketing ploy for some car manufacturer (I think maybe Ferrari?) who claimed their cars were so expertly designed and aerodynamically perfect that rolling down the window would have a serious effect on the mileage and power. Even if it was true for them, the effect for most cars is practically negligible-- if it is the choice between AC and windows, windows will yield better mileage 99% of the time.

The other posters are right, though, that nowadays the mileage drop from using the A/C is pretty darn low, but I suspect the mileage hit for having your windows is very close to zero.


Again, Consumer Reports debunked this myth in their recent issue. The mpg difference in driving with the windows open or closed was too small to measure! The drop in mileage with A/C on vs off was 1 mpg at highway speed. Much smaller than in the past. They also said that roof top carriers significantly reduced mileage.


Mike; the 7000 mile trip I took, had us visit many campsites in 1975. In nearly all, except some in Canada, I was ususally the only guy without A/C in my car. New Hampshire may be a place where the climnate is cooler and people are more frugal, and only 20% had A/C in the mid 70, but virtually all cars in California, Florida, and other warmer states had air.

In 1965 I took a 4 week computer workshop in Massachusetts, and again my 1965 Dart was one of the few cars without air. Most US companies by the 70s had standardized air on their copany cars, mostly to get more useful work out of their employees.

I would like some of the older psters to comment on this.