What About The AC?

[Yaris Hilton]

That could result in a mileage improvement, if the lower octane fuel was causing the engine's knock sensor to retard the ignition timing to limit the knock, making it burn the fuel less efficiently. This has been discussed endlessly in other threads.

[IllusionX]

The AC compressor runs regardless the fan at min or full blast. there is no advantages to not threat yourself the extra cold air.

I tend to try to turn off the AC when i'm driving in the city with lots of stop and go as the heat turns on the radiator fan on and off often.

[Zaphod]

And here I thought that running the fan at higher rpms increased the efficiency of the AC delivery.

What does the temperature control do, turn on/off the compressor at intervals?

[Yaris Hilton]

No, the compressor does not run continuously. It has an electric clutch. It cuts in and out keeping the cold air output at a constant temperature. When it's cooling less air, it runs less.

[scape]

Originally Posted by Yaris Hilton

No, the compressor does not run continuously. It has an electric clutch. It cuts in and out keeping the cold air output at a constant temperature. When it's cooling less air, it runs less.

one: I run my AC at 75%, just to add a bit of senseless input to this conversation :D
b: how often does gas not contain the proper octane rating, may you please link me to this thread you spoke of-- I'm rather interested :)

[R2D2]

Scape,

I don't believe Yaris is insinuating that the octane rating is improper-what he is saying is it is conceivable that using a higher octane fuel than recommended for the vehicle could result in better fuel economy.

This is potentially possible because the vehicles knock sensor prevents detonation by retarding the timing. Therefore a higher octane fuel MAY yield better fuel economy by allowing for more timing advance. It is this mechanism that would make gains possible as there is actually LESS energy in a gallon of premium gas than in a gallon of regular. I'm not a fan of running higher octane than recommended however because the octane rating actually indicates a fuels resistance to ignition and there is risk this could lead to deposit issues long term.

R2

[deerebilt]

your a/c system will last longer with fan at a higher speed and temp set warmer. this keeps more air moving past evaporator amd condensor cooler which in turn lowers radiator temp and a/c compressor temp thus longer life. and with a/c temp set closer to warm and fan speed higher compressor will run less and engine load reduced

[Yaris Hilton]

That's true, if the Yaris's AC control system is smart enough to cycle the compressor to reduce the cooling of the air to get a higher output temperature. Many systems run the compressor to chill the air coming out of the evaporator to a constant minimum temperature, and mix hot air from the heater core with the cold air to get anything warmer than the coldest temperature. In that case you don't save anything by running the temperature higher, but you do by running the fan slower as you're chilling less air.

[scape]

I always viewed the AC as a system of percentage, like how activated or open the coolant throttle may be for the system. I usually prefer 75% and number 2 fan, when people are in the car, I run the fan at 3 and front vents only (people seem to think cold dry air in the face means they are cooler, lol). I don't think the throttle is always fully open (can you call it a throttle?) and mixing with heater core temp (some cars do this, my bronco did!), but I don't think the yaris mixes heater air until 50% or below (then again this is all stipulation on my part!)

@r2: I agree about deposits, I gotta look up this pre-det problem with regular-- never heard of this and the knock sensor problem

[Kaotic Lazagna]

I use my A/C when there are others in the car at temp settings one click before max, and fan speeds of 2-3 on recirc on front/face vent. I'll notice a drop in mpg at this settings, but if I must use the A/C by myself, I'll have it to the same settings except for a fan speed of 1 and in between front/face and the front/feet setting (the dot). I haven't noticed a drop in mpg, and at times have actually gained mpg (probably due to me staying at a constant speed oppose to dosing off without the A/C and fluctuating my speed).

[gammaray]

Use the Recirculate setting to cool the interior quicker, with higher outside temps. Usually when your car has been sitting a long period and very hot inside. Then cut it off. Back to the fan speed...... It does not affect mileage.

[CtrlAltDefeat]

Actually the interior of the car, on a hot day, can get well above the ambient temp outside. From what I figure, it's best to turn the ac on lowest fan/coldest temp/outside air and roll the windows down until the interior temp reaches the same as the outside. Then you switch to recirculate. When the air con is outputting cold air, change the temp to the middle/cool setting, and turn up the fan. When the AC is first turned on, a high fan speed will wick all of the cool out of the coolant, and the AC will run longer before getting cool. This is all just imho, but I think my logic is correct...

[BailOut]

Originally Posted by Forrest

No longer keep track of mpg's...as the little car always does well. As far as AC is concerned, if it is hot in the car...use it. Driving in a comfortable temperature sure beats driving around on a warm day and cooking inside a car..regardless how much extra fuel you may use.....better to be comfortable.

Originally Posted by Henry G.

Word.
You already saved a bunch of money by buying a cheap underpowered jap car that gets good mileage, why torture yourself sweating inside a car youre making payments on? Buy premium too and live a little..my mileage went up 1.5 to 2 mpg in the hot weather just by buying premium, the car likes it under load (I drive hard), live a little cheapskates.

It is disheartening to see comments like this in the Fuel Economy forum. Gasoline mostly comes to us from countries and regions that are not friendly to us, we have already spent many human lives to ensure its supply and the death toll continues to rise, and even with modern technology every drop of gasoline burned releases lots of harmful emissions. As such each of us has the personal responsibility to not use more of it than is necessary.

I'm not saying that there isn't a time to use a/c but to be flippant about it is arrogant and wasteful.

As to the comment about higher octane netting higher MPG, to summarize hundreds of posts on at least 2 different forums: Those that drive frugally will see a large MPG loss with higher octane fuel as it is harder to burn it, while those that drive aggressively often see a slight MPG increase with higher octane fuel due to less ignition retardation. Even so, the much higher price of higher octane fuel rarely makes economic sense as compared to the minimal MPG gain. Additionally, without constant and consistent mileage logging a change of just 1 or 2 MPG is impossible to quantify.

Buying a fuel efficient car is a definitive start on the right track, but it is only the beginning. The change that is most needed is within the driver, and in their driving style.

[Yaris Hilton]

Originally Posted by gammaray

Back to the fan speed...... It does not affect mileage.

The fan itself doesn't, but it does because you're cooling less air with the compressor when the fan's turned down.