Better MPG w/ A/C ON????? How the heck??????

[redgtxdi]

'95 Geo Prizm.........1.6L w/ 3spd auto........(total slug!...LOL!!)



Anyway, I'm noticing that I seem to get better gas mileage with the A/C on!! I know that turning the A/C on will typically bump the idle a couple hundred rpm at idle, but how the heck can I be getting better MPG with the A/C on than with it off if it's obviously putting more load on the motor???

FWIW, I hardly ever get on the freeway and I live in So Cal so it's red lights & stop signs for me all day long!

I typically average around 22-23mpg w/ NO A/C, but *with* the A/C on I usually get 23.5-24mpg. I'd say it's not significant enough an increase, but I *should* be getting less and instead I'm getting *more*! I typically get 200miles, then fill up with 9.0 to 9.2 gallons like CLOCKWORK!

With the A/C on it's close to 8.5 gallons per 200 miles!

???

[todds21]

less wind drag with the ac on maybe....that is assuming you have windows down when ac is off?

[redgtxdi]

Well, good guess, however at my city speeds that probably wouldn't do it, plus I almost never drive with the windows down. It's either vent, air or heater.


Any other guesses??

[freakinbox]

just in your head?

[Amber]

Could there be a slight timing change (ECU controlled) to offset the load the A/C puts on the system? And that lead to better mpg's?

[redgtxdi]

Good question! I really don't know!!

I know in carburetion there are many circuits and typically turning on the A/C increases the idle circuit so as to supplement idle rpm. That can get nullified as rpm's increase, but at worst case that'd still mean higher fuel consumption at some percentage even if nothing more than idle.


As for fuel injection, I'd assume it's just an ECU control signaling the injectors to up the fuel a bit. I know it's working properly 'cuz if I turn the A/C on/off the motor does adjust appropriately. I'm just totally baffled as to how I get better mpg with the A/C on!

Oh well.........guess I'll just have to freeze thru the next winter............LOL!!!!!!!!!!

[Flashmn]

EFI controls the intake air valve to supply additional air, which in turn in map sensored vehicles increases fuel delivery and thats why RPM rises too, you're sorta opening the throttle.

[redgtxdi]

Originally Posted by Flashmn

EFI controls the intake air valve to supply additional air, which in turn in map sensored vehicles increases fuel delivery and thats why RPM rises too, you're sorta opening the throttle.

OK, that explains that! Thanks for that!!!


Now, care to take a guess at my pleasantly confusing quandary??

[JeffG]

perhaps and its just a guess... you go slower from a stoped red light upto speed with the a/c on. With the a/c off you have more ummph and thus go faster from a stop upto speed ie jack rabbit starts...

[JohnO356]

I'll bet you've hit it, Jeff. When I drive either my Corolla or my truck with the A/C on, i consciously start out easier from a light, stop, etc. My thinking has always been that the engine is working harder already, why push it more.

[redgtxdi]

And here's another curveball........

While that's also a good guess, it's the opposite of what I do.......and only out of necessity!!!

For anyone with the 1.6L hooked up to the 3spd auto, you know what a slug these things are! Turn on the A/C & forget about it!

I'd say I *definitely* apply more throttle when the A/C is on only 'cuz the shift from 1st to 2nd leaves the car in an almost standstill. If you don't put your foot in it 'til you get the rpm's up, somebody will drive right thru the back of you.......LOL!!!

So that ain't it either!!

Heck, I wish I could bottle air-conditioned air & sell it........I'd make a fortune w/ my car!!

[sonyminidiscman]

Originally Posted by redgtxdi

And here's another curveball........

While that's also a good guess, it's the opposite of what I do.......and only out of necessity!!!

For anyone with the 1.6L hooked up to the 3spd auto, you know what a slug these things are! Turn on the A/C & forget about it!

I'd say I *definitely* apply more throttle when the A/C is on only 'cuz the shift from 1st to 2nd leaves the car in an almost standstill. If you don't put your foot in it 'til you get the rpm's up, somebody will drive right thru the back of you.......LOL!!!

So that ain't it either!!

Heck, I wish I could bottle air-conditioned air & sell it........I'd make a fortune w/ my car!!

I hear u man.............its soooooooslooowwwwww when the damn a/c is on... thats y on start ups and going onto the highway, i turn my a/c off... otherwise, those 18 wheelers will go faster than I am.

[redgtxdi]

Ahhhh yezzzzzzz..........slow..........BUT.........

PAID FOR!!!!!!!!!!!

[Flashmn]

Do you drive alot on the highway? with the window(s) open you're creating alot of additional aerodynamic drag that the car has to overcome.