My question is… in different scenarios of use of the air conditioner is gas affected in any way? For instance would it be better just to have the windows cracked for a breeze, and the feet air conditioner on at 70degrees rather than 60. Or just put it on however since its already on and using gas anyway?

Scenarios I could think of:

Running the air conditioner on high or low (fans), colder than cold enough? Rec. Air or Air from the outside? Just the feet, or just the defroster?

- mitch

edit: Wow I didn't realize this was my first post... I'll introduce my self, I'm Mitch and just recently bought a 2003 350z base model(silverstone), and I'm a long time forum user, but I'm new to this one. whats up all.

 

From what I have read driving with your windows down, equals drag, which decreases gas mileage. They say to use the A/C but of course not full blast.

I seem to not have a problem with my windows down, Welcome to the forum.

 

AC in stop and go traffic sucks gas quick, better to use windows unless its unbearable.
AC on freeway is very efficent and better than using the windows.

 

not using the A/C will also win races and improve your quarter mile times. it is just as much of a boost when u take Traction Control off.

 

I was thinking beyond this statements... more technical like having the fan on full blast make that much of a difference? And Temp. wise too. But hey thanks for all the quick replys I feel so welcome.

 

it shoudlnt make much of a difference when your gas money comes into play if your worried about consumption it prolly affects it a little bit, but nothing to worry about... I was being funny abou quarter mile times, but it is very true that ur faster without A/C......i also heard when u turn on the heater for hot air, close ALL your vents so the air is not comin in the cabin.....this supposebly hot air cools down the engine....my friend used to do this with his turbo civic...lol

 

Yes, that is true about your heater, I had to do it in a s-10 beater... I'm not really concerned about the gas cost, I merley thought about it today, because I was satisifeid with the a/c on, but then I rolled down my windows a little bit, and turned the feet a/c on. Then low and behold I was stumpped and couldn't decide which used more gas.

 

i dont give in the fact that rolling down the windows affects gas mileage unless your going really fast where wind is blowing fast enough to make the hair on your arm stand up. Anyway did u know auto is the highest setting..correct me if im wrong.

 

I thought the compressor was always putting the same amount of drag on the motor, regardless of fan speed.

ive tested this situation out at low and high speed cruising. i used a/c with windows shut, windows open, and windows closed scenarios. Didn't see too much of a difference, maybe 2mpg or less for the AC at low speed, same at high. windows only affect the efficiency at high speeds, but decreased about the same amount as ac with windows closed.

 

[QUOTE=SBT]I thought the compressor was always putting the same amount of drag on the motor, regardless of fan speed.
[QUOTE]

correct. if your a/c button is on (or you're in defrost mode) your compressor clutch will be activated and your engine will be turning your compressor. doesn't matter what temp setting you have it at, the compressor is turning and the energy comes from the engine. the compressor will cycle off on only 2 conditions: refrigerant pressure is too low or too high. it cycles off for 5-10 seconds depending on the PCM calibration then it turns back on.

cycling too much will put more wear on your compressor clutch.

so what causes a low pressure cycle off? it's basically when you're evaporator core is icing over, ie your AC system is cooling the core so much the condensate is freezing on the core. if the outside ambient is not that hot, and you have it on low blower fan, you'll cycle off on the low pressure switch. turning up the blower fan helps because it keeps as much warm air as possible moving over the evap core.

to cycle off on the high pressure switch, outside ambient has to be really hot (or engine temps are really hot), and you have low airflow through the condenser (ie, you're at idle in traffic for 30 minutes).

now guess what i do for my job. ha!

 

right on... so persay I'm wasting away gas(running the a/c). I may as well make it as cold as I want, and let it blow as hard as I want? But if at full blast I'm harming the compressor clutch?

 

Welcome! I think that the AC definitely affects your gas mileage and your performance because it's creating additional stress on the engine. I think that running it at just about any setting or speed (maybe a tiny difference between full blast and barely on) it's gonna put about the same strain on the engine.

 

Cruise with the windows down and the AC off. You will use less gas.

 

In the Nissan Z manual it specifically states that you will get LOWER gas milage if you drive with your windows down at highway speeds. So just use the A/C under those circumstances. Much quieter as well.

 

Mythbusters did an experiment in Chevy Suburbans. Two trucks with equal fuel around an oval track at 40mph. One had A/C on and one had the windows down. The one with the A/C went MUCH further before running out of gas.

That seems to be my experience in the Z too, with the majority of my driving in the city.

 

Ive posted this and been flamed but oh well, I will post my crazy results again. My car avg 28mpg at 70mph on the high way with windows up or down, ac off. Doesnt change. With windows up and ac on, i get 30 mpg at 70 mph. Strange huh. Ive been doing these test over and over for almost 8 months now. I not only do the test using my cars computer but I also go by miles travelled over like 400 miles and actual gallons of gas filled and then pull out my trusty calculator. lol BEN

 

Today I got 35.9 mpg cruising behind a pack of cars (not tail gating there were atleast 3-4 car lengths). AC on and the windows up. AC was on the lowest setting!

I'm impressed with the MPG on our big 3.5 engines.

 

i get 22.5 mpg on avg with 80% freeway driving. I think the gas sucks. I only have 2,000 miles on my car though, so maybe it gets better???

 

Yes, the 350z manual actually states very clearly that to; maximize fuel economy; to run the AC instead of opening the windows when traveling on the highway. That the 350z's aerodynamics are such that disturbing the airflow with the open windows produces much drag.

Of note, I get 17mpg city and 25mpg highway. Slightly more for both if I don't drive like a maniac....which is almost never.

 

Wow, I knew that with the windows down that cars produced drag, but I would have never thought it to be strong enough for the maker to write it down in the manual. I will now be flying down the interstate in comfort, peace and free of worries.

Thanks all - Mitch