How much gas does AC really eat up? I've always been told, the more I use my AC the more gas I will use. Thanks for the input.

 

A/C eats very little extra gas. Driving with the windows open and the A/C off is about the same as driving with the windows closed and the A/C on because of the aerodynamic effects.

The difference is so small you might as well be comfortable.

 

There was a Myth Busters episode about this topic... Don't remember the results.

 

also would the AC slow down your acceleration?

 

I normally get 24mpg now in the summer running AC it's 23. I'll take the hit. My H2 is getting about 6

 

Yes...the car is slower with the AC on and yes buy the A-Spec kit

 

i remember looking this up before, if i remember using the AC can eat up to 20percent more gas in stop and go traffic, and uses about 8hp from your engine, and i remember something about 3mpg

i do notice on my TL that when i shut off the AC i get better acceleration but this is probably cause my car doesnt have nearly as much HP as a 3G TL

 

The mythbusters results were that it uses less gas to run the car with the windows up and the AC on then the windows down and the AC off, drag overpowers the compressor. As far as acceleration, yes, it will take a hit, but the compressor goes off at high RPMS.

 

Last Sunday, I traveled to Fredericksburg, VA, averaging 62 MPH with an outside temperature in the mid-80's. I used the A/C the whole trip and managed 32 MPG.

Not too bad, I'd say for my '04 manual transmission TL.

 

Ummm hopefully you just have a poor memory but the actual results were that the expedition not running the AC went like an additional 20 laps around the track. Adam's expedition (running the AC) went significantly less distance than Jamie's (without AC). They had no means as to explaining it because they basically had identical vehicles with the same weight and volume of gas.

 

I've never calculated the difference in MPG between a/c driving and no a/c driving, however I did have one experience that might provide a clue.

Back in the late '90s I ended up taking my '93 Camry V6 to the local drag strip. I was supposed to take the Dart, but it was too hot, so I took the Camry instead.

I would run the a/c while waiting to run and after each run. I would turn off the compressor during every run on the 90 degree high humidity day.

My car was running consistant low 17s despite the heat in humidity, except for the one run where I forgot to shut the compressor. That run was an 18.3.

I *assume* if the compressor can provide enough power drain on the engine to slow the car significantly, then it must be impacting fuel mileage. Of course the drag of running at highway speeds with windows down may offset any benefit of leaving the a/c off.

Your mileage may vary...

 

 

I'm going to have to say, with my commute and driving environment, I get between 2-3 mpg less with the AC on. As mentioned above, I would also say the loss of mileage is greatest with the AC on given "more" stop and go driving. My commute is atleast 80% highway and the rest minor stop and go. I easily get 29 mpg with the AC off in the fall and 26 in this 90+ weather.
(2004 5AT TL)

I also agree with taking the hit to stay comfortable

Todays quote:

"A sweaty ass may causes butt prints"

Cheers

 

there is a significant difference between running with the a/c on and off (a few mpg). but is it really worth it? you are driving around in a nice car don't you want to be comfortable?

 

 

windows down + high speed < windows up w/a/c fan setting at 1 + high speed

 

I know my 911 will clutch out the A/C if I floor it so as to not drain HP when it's needed.
The TL does not do this as far as I can tell. There is a difference in HP, and I would imagine that percentage difference in HP probably equals close to the percentage difference in mileage.

Living in Houston, I don't care if my miles per gallon drops by 75%, I'm using the frickin' A/C!

 

The difference is actually very small. I'm averaging maybe 1 - 2 mpg less, which is nothing. Off the start, the car is slower that's a fact, but yes, having the windows open during driving actually slows your car, effecting you gas mileage. Plus, who would not use ac during these dog days in the NE.

 

Maybe not during accel, but the TL will clutch out the AC at high RPMs, as will most cars.

 

as far as the mythbusters issue goes, the problem was that the *computer model* said it would be more efficient at 55-60mph to use the a/c. they limited themselves to 35mph on the track and subsequently that shoots down the model. at 35mph the a/c isn't very efficient so the vehicle with the windows down ran for more laps before running out of gas.

on the highway doing a straight trip i never see a difference in my gas mileage with the a/c on. i consistently get 31-32mpg on long trips. at 55mph the TL is only putting down 11hp (i know because it says so on my last dynosheet). now mind you this does not include, a/c use, going uphill, turning the headlights on and dragging the alternator down, etc. but at 55 on the highway you are better to use the a/c because it is not much of a strain at that point. the engine has enough kinetic energy and is spinning fast enough to offset the drag from the compressor. besides, some people might now know that the compressor isn't always engaged either. it only cycles when it needs to.

in town is another story. i personally leave it on because i want to be comfortable.

SSTS

 

An AC compressor that modulates or cuts in and out was put in cars in 1977. My 74 monte carlo had a compressor that ran 100% of the time and it was so cold that on the hottest day I could but it on the lowest fan speed at 95 degrees out and stay cold. In 77 they made the change for economy... Sure you saved some fuel, but the air is no where as cold as it was back then...

So this feature has been around for almost 30 years.

 

Based on my MID my AVG MPG for a tank is the same with A/C on in highway driving. My city MPG AVG dropped by 1. Also, I don't like the Auto features on the A/C. Here in Florida my A/C is on Manual @ 58F all the time in the summer, I just adjust fan speed and vent directions.

 

Here's a little trick you can do that will provide surprising results.

Our TLs have a super auto HVAC setting.. it does a great job of keeping the cabin comfortable. EXCEPT under certain conditions. Ever notice on a hot, humid day how long the auto setting keeps the air on RECIRCULATE? On humid days, this can cause a problem.. namely evaporator coil freeze-up. This causes a loss in cooling efficiency, raises the humidity levels in the cabin, and ceases to perform at its best. You can tell your coil has water or ice on it if you manually select outside air and you smell moisture coming from the vents.

So you can do one of two things. Shortly after selecting AUTO, switch to outside air. Or do as I do for shorter trips, like to and from work or stores or such, and don't even use AUTO at all.

What I do when driving around in the nice weather is set my MODE to upper vents only, the fan on 2 or 3 (or 4 if needed), and the temperature to "Lo". Then when I want the A/C, I just turn on the A/C switch. The air which comes from the vents is very shortly quite cold. And no coil freeze-up or lingering odor. I do this most of the time. Yesterday, it was 93 degrees here with fairly high humidy. I left work with the temperature set at 66. Within 10 minutes, I had set it to 68, and about 20 minutes later to 69.. it was getting darned cold in my TL.

Try this method and see if it serves you as well as it does me. I used to do this with my last car, too.

 

Temp change from older cars to newer cars has to do more so with the transition from R-12 to R-134A, R-12 was significantly better then R-134a, too bad its 50 a can and you need a special licence.

 

Modern auto A/C units are just as good, if not better, than those made in past years, even without freon. My last car, a 2002 Altima SE, put out the coldest air of any car I've ever owned. The next coldest is a tie between my 1996 Ford Contour and my TL. All of these cars used, and use, 134A refrigerant.

While the freon scare with ozone was a crock, we've seemed to make out just fine with the 134A.. after the initial bugs.

 

They both use freon, R-12 and R-134a are both types of freon. And R-12 really is worse for the O-zone, it contains more CFCs, although both are bad for the O-zone. although global warming is BS, cause it aint happening(read State of Fear by Chrihton). If you were to empty the R-134a From your AC unit and fill it with R-12 it would get colder and colder faster.

 

Yes, I agree that R12 and R22 are better than 134A, but after the initial problems (oiling failures, leaks, fires), the 134A does work.

I don't buy global warming, either. But that's a different topic I'm sure will cause both visceral reactions and a thread move from this site, eh?

 

once on a trip i looked at my miles to empty i forgot what the exact number was at the time but i turned the ac off and after a few seconds it added 2-4 miles on it.

 

Nice post. I'm going to give this a try. I tends to get fairly hot and humid in Houston!

Question, why does recirculate make the evaporator coil freeze up?

 

I took a three hundred mile round-trip yesterday. I reset my trip computer at the start, and got an average 27 MPG with an average speed of 55MPH.

I had the a/c running for the entire trip, and had the moonroof open for at least 1/3 of the total miles.

I'm pleased with the fuel mileage on the trip regardless of the slight fuel savings I sacrificed by using the a/c. The 1 MPG or so increase I might have seen wouldn't have offset the decrease in comfort.

 

This is the main reason I got rid of my tsx and got an 05 tl. In northern virginia 90 degrees feels like 110 with your balls stuck to your ass because of the humidity. I go to virginia beach allot with my wife because thats were she is from and 95 the average speed is 75-80. In the tsx it was fine in the winter until you had the trunk full, my wife her friend and the ac on. I would try to pass someone and watch grandma pass me in a crown victoria. The tsx must have lost 40% of its power with the ac on. I mean it was like night and day. Now with my tl its like no power loss, its awsome. And allot more rear seat room from what passengers tell me.

 

The TSX also has 70 less horse power and 72 less Lbs of torque. The overall weight saved in that vehicle over the TL is also about 300 pounds. You get more power per pound on the TL than on the TSX, which could be considered underpowered. As for AC robbing that much power, that is incredably unlikely, at least I have never heard of an AC compressor taking more than 15 HP, and even that is high, such a large power decrease could be at low engine RPMs I guess, where the car is not putting out nearly all the horses it has.

 

To Scott in Houston;

You can get evaporator coil freeze up with the outside air, too if the humidity is real high and the coil gets too cold, or if the airflow is restricted or if your fan speed is set too slow.

With recirculate on, the humidity in the cabin raises because of the passengers. Their bodies produce heat and they breathe. So it's a vicious cycle.

With outside air coming into the cabin, you are constantly replacing the interior air so the coil has less chance of freeze up. I did have a coil freeze up with one car on outside air once. Our family was going to Charlottesville for my oldest daughter's graduation from UVA. A very hot day and taxing for my wife's '91 Honda Accord LX. The coil froze up to the point of completely disabling the A/C. When we left Charlottesville, all of the ice had melted and everything worked fine on the way home.

 

Are there any actual benefits to recirculating the air, besides it being slightly cooler.

 

To crazymjb;

No, except for quicker initial cool down (unless it's really humid) or if you happen upon a dead skunk or get behind a smelly vehicle.

 

First of all, to the guy that said global warming is BS: in the furture, I would try to aviod getting your facts from a fiction writer. While Crichton is a moderately entertaining novelist, he is NOT a scientist/research/expert in any way. Before making bold comments, have more than one source, and make sure at least one is credible.

In regards to A/C power loss: I'm not sure about the 3g, but I know my 2000 TL has a neat little feature where if the A/C is on and you ask for lots of power (ie floor the gas/go up a hill) the compressor will actually be shut down by the ECU until more power is available. Keep in mind the fan is still blowing, but you'll be able to feel the air get wamer for a few seconds. Then, the commpressor will power on again and the air will go back to being cold.

 

Mythbusters results: 15 % difference (better fuel economy with windows down). THe way they did it was to fill up 2 explorers with a gallon of gas and then go around the track at cruising speeds. The results would be different (actually worse for driving with AC, I would guess around 22 ~ 25 % ) in stop and go city traffic.

I hate driving with windows down I think I have hardly rolled down my windows 5 times in 1 year (except for letting out hot air or openning them at a drive thru)

Plus hate the fact that I (and most of us here) spend all this time cleaning up and keeping out interiors clean and then one HWY drive with windows down can put all this dirt and other junk in the car.

 

Have to Disagree with you Southernboy

There is definitely more than one reasons where recirculating air is beneficial...

You are circulating air from your cabin which is cooler then outside air (apart from the first time you sit in your car)

By circulating cooler air from you cabin

1) You compressor has less load as it does not have work as hard to cool
down the hot outside air.

2) You get better gas mileage since your compressor is not working as
much

3) Better power again as your compressor is working "less"


Best option on the TL I have found is to put it on AUTO, it works like magic, it will not recirculate if the inside temp is higher than outside...once the temp difference has flipped it will start recirculating and also as some one mentioned before It will cut-off the AC for more power if you rev up your engine (eg. while getting on the hwy etc)

 

Its not only the HP and Torque the CC of the engine also plays an important part...(eg. the TL with 3.2 liter can not tow 9000 lbs like a Tundra with a 5.7 liter)

40 % power rob sounds like pushing it also at cruising speeds on hwy (I would imagine the sluggishness would be noticed only in city traffic) but again I dont have an TSX with load and AC experience so dont have a comparision.

 

Air compressors in our cars, does it have "low or full" running mode? or is it simply On or Off type?