AC question!!! Which saves more gas?!?!

JZNx · 08-25-2011, 03:22 AM

So...
I probably been thinking about this topic for last couple of years...
But the way I use the air condition in my car is always been the same...
I only use AC during summer and never use it during winter...

But if I use the AC, I always put it to the coldest setting and turn it to the lowest level. If I get cold in between I turn off the AC. Then if I get hot again I turn it to the lowest level. Back and forth... So like on a long drive, I would turn it on and off quite few times... Now does this save gas compare to leaving the AC on all the time but adjusting the temperature? Of course level being set to the lowest level.

Anyone know this? I googled enough and wasn't really lucky with it... lol...

Thanks for reading guys =)

houkouonchi · 08-25-2011, 05:08 AM

I don't know for sure I am guessing it does (save gas/energy). I usually do the same as you though although I typically don't have to turn it off very often.

Lately I have found myself turning the A/C on even when its pretty damn cold out simply because its too humid out. Seems like its been more humid than usual this summer.

kensin0429 · 08-25-2011, 07:02 AM

on all the time, coldest seting and nob is at 2 oclock position

BOLIO 671 · 08-25-2011, 07:35 AM

Same here...I use the A/C all the time in the same fashion since I live in a tropical climate...The only weather we have here is Sunny or Rainy...so U need the A/C pretty much of the time...and a full tank of Gas usually lasts me about two weeks.

I also heard that the Z has a sensor that will turn off the compressor of the A/C wen u get on the gas/throttle...Does anyone know if there's any truth to this?

Snakes709 · 08-25-2011, 08:11 AM

only time i use the a/c is if im on long road trips on the highway and if its really hot. The Z didnt have a huge issue buy my Evo does. Damn thing nearly stalls at when im at a light with the a/c on...thing sucks so much power from the car its unreal.

wstar · 08-25-2011, 08:35 AM

If cycling your AC on and off manually saves gas, it's just because you're making the average temperature higher than it would be if you left it on all the time at the coldest setting. In any case, even on older cars the A/C compressor cycles on and off while you have it "on". It's just part of how the whole system operates.

The A/C in the Z is thermostat controlled anyways. IMHO, set all the dials to "Auto" and set the temperature at your comfort vs cost limit. The colder you set the dial, the more gas you'll suck over time. It will be far less trouble and just about as effective.

A related issue that's been debunked before: rolling down the window vs running the A/C. Assuming you can bear the heat level of running with the windows down and no A/C to save gas, it actually does save gas at low speeds (city streets). However, on the highway, the parasitic drag on the car from having the windows open wastes more gas the running the A/C, so don't do that.

PapoZalsa · 08-25-2011, 08:43 AM

I keep it on during the Summer at a comfortable setting.

DaveyG · 08-25-2011, 09:12 AM

Quote:

Originally Posted by wstar

A related issue that's been debunked before: rolling down the window vs running the A/C. Assuming you can bear the heat level of running with the windows down and no A/C to save gas, it actually does save gas at low speeds (city streets). However, on the highway, the parasitic drag on the car from having the windows open wastes more gas the running the A/C, so don't do that.

So true, I wish people would understand this. I swear I always run into people saying ac uses more gas no matter what. Either you understand physics or you don't I guess.

Vaughanabe13 · 08-25-2011, 09:21 AM

Quote:

Originally Posted by JZNx

So...
I probably been thinking about this topic for last couple of years...
But the way I use the air condition in my car is always been the same...
I only use AC during summer and never use it during winter...

But if I use the AC, I always put it to the coldest setting and turn it to the lowest level. If I get cold in between I turn off the AC. Then if I get hot again I turn it to the lowest level. Back and forth... So like on a long drive, I would turn it on and off quite few times... Now does this save gas compare to leaving the AC on all the time but adjusting the temperature? Of course level being set to the lowest level.

Anyone know this? I googled enough and wasn't really lucky with it... lol...

Thanks for reading guys =)

This sounds completely false to me but I don't have any scientific data to back that claim up.

RandyD · 08-25-2011, 09:38 AM

gut reaction: let the Auto modes do the work. Turing your car into an icebox 3 times on a trip then letting it heat up seems much more wasteful than just letting it settle into 75 and staying there.

however, the cabin is pretty small compared to most cars, so it is probably cheap anyhow to cool it off.

hard for me to tell since i just go with the top off everywhere.

Red__Zed · 08-25-2011, 09:52 AM

Quote:

Originally Posted by DaveyG

So true, I wish people would understand this. I swear I always run into people saying ac uses more gas no matter what. Either you understand physics or you don't I guess.

It's more of a fluids question...

...but at 70 or so, most cars use about 2.5% more gas with the windows down, and 5% more with AC on, so.....

wstar · 08-25-2011, 10:17 AM

Mythbusters tested this (measuring fuel consumption and efficiency in real cars), and then went back and revisited the issue after comments and concerns and re-tested. Wikipedia's final summary of their final summary:

The fundamental flaw in the MythBusters' test was that the point where the drag becomes powerful enough to inhibit a car's performance with windows down was inside their 45–55mph margin at 50mph. Going less than 50mph it is more efficient to leave the windows down, but going greater than 50mph it is more efficient to use the A/C.

ETA: It's probably a reasonable assumption that the 50mph figure will vary depending on the aerodynamic configuration of the car and the windows, as well as other differences affecting the A/C compressor's efficiency. But it's a reasonable ballpark, and reasonable cars' break-even point probably doesn't vary a whole lot.

cossie1600 · 08-25-2011, 10:32 AM

really, worrying about the ac on a 3.7l?

Waiz · 08-25-2011, 10:48 AM

Quote:

Originally Posted by wstar

If cycling your AC on and off manually saves gas, it's just because you're making the average temperature higher than it would be if you left it on all the time at the coldest setting. In any case, even on older cars the A/C compressor cycles on and off while you have it "on". It's just part of how the whole system operates.

The A/C in the Z is thermostat controlled anyways. IMHO, set all the dials to "Auto" and set the temperature at your comfort vs cost limit. The colder you set the dial, the more gas you'll suck over time. It will be far less trouble and just about as effective.

A related issue that's been debunked before: rolling down the window vs running the A/C. Assuming you can bear the heat level of running with the windows down and no A/C to save gas, it actually does save gas at low speeds (city streets). However, on the highway, the parasitic drag on the car from having the windows open wastes more gas the running the A/C, so don't do that.

Great post, very informative!

OP, I do the same thing as you and the difference is barely noticeable.

DJ-of-E · 08-25-2011, 02:02 PM

Unfortunately, it still kinda sucks about the whole windows thing.

I mean, if you're on the freeway, you'd use AC because of parasitic drag. When on the street, you use AC on a warm day because windows do nothing but stay the same with ambient temperature at the stop.

08-25-2011, 03:22 AM	#1 (permalink)
JZNx Base Member Join Date: Jul 2011 Location: **SoCal Posts: 246 Drives: 370z Rep Power: 14	AC question!!! Which saves more gas?!?! So... I probably been thinking about this topic for last couple of years... But the way I use the air condition in my car is always been the same... I only use AC during summer and never use it during winter... But if I use the AC, I always put it to the coldest setting and turn it to the lowest level. If I get cold in between I turn off the AC. Then if I get hot again I turn it to the lowest level. Back and forth... So like on a long drive, I would turn it on and off quite few times... Now does this save gas compare to leaving the AC on all the time but adjusting the temperature? Of course level being set to the lowest level. Anyone know this? I googled enough and wasn't really lucky with it... lol... Thanks for reading guys =)

08-25-2011, 07:02 AM	#3 (permalink)
kensin0429 Base Member Join Date: Aug 2009 Location: palmsprings Posts: 244 Drives: 370z Rep Power: 16	on all the time, coldest seting and nob is at 2 oclock position __________________ 10 40th AE Z

08-25-2011, 07:35 AM	#4 (permalink)
BOLIO 671 A True Z Fanatic Join Date: Mar 2010 Location: GUAHAN Posts: 1,198 Drives: To & From then Back Rep Power: 3399	Same here...I use the A/C all the time in the same fashion since I live in a tropical climate...The only weather we have here is Sunny or Rainy...so U need the A/C pretty much of the time...and a full tank of Gas usually lasts me about two weeks. I also heard that the Z has a sensor that will turn off the compressor of the A/C wen u get on the gas/throttle...Does anyone know if there's any truth to this? __________________ 2013 Nismo Z34 / FI TT #091 / IG: @lilzilla_z34

08-25-2011, 08:11 AM	#5 (permalink)
Snakes709 A True Z Fanatic Join Date: Aug 2009 Location: Edmonton Posts: 1,205 Drives: 2011 Evo-X GSR Rep Power: 18	only time i use the a/c is if im on long road trips on the highway and if its really hot. The Z didnt have a huge issue buy my Evo does. Damn thing nearly stalls at when im at a light with the a/c on...thing sucks so much power from the car its unreal. __________________ 2011 Evo-GSR AMS 2.4 stroker/ bore, FP Black build in progress. Sponsor: DSG Performance

08-25-2011, 08:35 AM	#6 (permalink)
wstar A True Z Fanatic Join Date: Mar 2009 Location: Houston, TX Posts: 4,024 Drives: too slow Rep Power: 3594	If cycling your AC on and off manually saves gas, it's just because you're making the average temperature higher than it would be if you left it on all the time at the coldest setting. In any case, even on older cars the A/C compressor cycles on and off while you have it "on". It's just part of how the whole system operates. The A/C in the Z is thermostat controlled anyways. IMHO, set all the dials to "Auto" and set the temperature at your comfort vs cost limit. The colder you set the dial, the more gas you'll suck over time. It will be far less trouble and just about as effective. A related issue that's been debunked before: rolling down the window vs running the A/C. Assuming you can bear the heat level of running with the windows down and no A/C to save gas, it actually does save gas at low speeds (city streets). However, on the highway, the parasitic drag on the car from having the windows open wastes more gas the running the A/C, so don't do that. __________________ 7AT Track Car! Journal thread / Car setup details

08-25-2011, 05:08 AM	#2 (permalink)
houkouonchi Enthusiast Member Join Date: Jun 2010 Location: Ontario, California Posts: 440 Drives: '14 GT-R '10 M6 370z Rep Power: 15	I don't know for sure I am guessing it does (save gas/energy). I usually do the same as you though although I typically don't have to turn it off very often. Lately I have found myself turning the A/C on even when its pretty damn cold out simply because its too humid out. Seems like its been more humid than usual this summer.

08-25-2011, 08:43 AM	#7 (permalink)
PapoZalsa A True Z Fanatic Join Date: Nov 2009 Location: Not in Sunny Florida Posts: 6,358 Drives: 16 Nismo w/Tech Pack Rep Power: 4499	I keep it on during the Summer at a comfortable setting. __________________ 2009 370Z MB Base w/Sport Package 6MT Modshack's Custom Air Intakes /3M Clear Bra/ Illuminated Kick Plates / F. I CBE w/12" resonators / EVO-R Front Lip / Rear Hatch Wing / Tein S-Tech Springs /Ilegal Tint in the Rep. of VA/4x20mm Z1 Spacers/ Vinyl Roof/Liquid Carbon Designs

08-25-2011, 09:38 AM	#10 (permalink)
RandyD A True Z Fanatic Join Date: Mar 2011 Location: Potomac Falls, VA Posts: 2,977 Drives: 2010 370z 7AT Roadst Rep Power: 20	gut reaction: let the Auto modes do the work. Turing your car into an icebox 3 times on a trip then letting it heat up seems much more wasteful than just letting it settle into 75 and staying there. however, the cabin is pretty small compared to most cars, so it is probably cheap anyhow to cool it off. hard for me to tell since i just go with the top off everywhere.

08-25-2011, 10:17 AM	#12 (permalink)
wstar A True Z Fanatic Join Date: Mar 2009 Location: Houston, TX Posts: 4,024 Drives: too slow Rep Power: 3594	Mythbusters tested this (measuring fuel consumption and efficiency in real cars), and then went back and revisited the issue after comments and concerns and re-tested. Wikipedia's final summary of their final summary: The fundamental flaw in the MythBusters' test was that the point where the drag becomes powerful enough to inhibit a car's performance with windows down was inside their 45–55mph margin at 50mph. Going less than 50mph it is more efficient to leave the windows down, but going greater than 50mph it is more efficient to use the A/C. ETA: It's probably a reasonable assumption that the 50mph figure will vary depending on the aerodynamic configuration of the car and the windows, as well as other differences affecting the A/C compressor's efficiency. But it's a reasonable ballpark, and reasonable cars' break-even point probably doesn't vary a whole lot. __________________ 7AT Track Car! Journal thread / Car setup details

08-25-2011, 10:32 AM	#13 (permalink)
cossie1600 A True Z Fanatic Join Date: Jun 2009 Location: californee way Posts: 5,380 Drives: 370, Leaf Rep Power: 30	really, worrying about the ac on a 3.7l?

08-25-2011, 02:02 PM	#15 (permalink)
DJ-of-E Track Member Join Date: Apr 2011 Location: Garden Grove, CA Posts: 676 Drives: 00 Toyota Celica 040 Rep Power: 15	Unfortunately, it still kinda sucks about the whole windows thing. I mean, if you're on the freeway, you'd use AC because of parasitic drag. When on the street, you use AC on a warm day because windows do nothing but stay the same with ambient temperature at the stop. __________________

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