I've always driven my cars with A/C on, but have recently stopped and taken to doing all my local driving with the front windows open and the A/C off. I am seeing a slight jump in MPG's, but too soon to run the numbers. Highway cruising is still in my windows up - A/C on mode most of the time, however. Wind buffeting is simply too much.

So I'm interested in what others have experienced concerning the use of A/C and the effects on MPG's. Actual - Factual - Incidental - what are you seeing?

K_C_ EDIT: I'm not too concerned w/ the window open/closed issue - though I guess it applies - more about A/C on/off.

 

Ive seen that it doubles gas usage at idle, but any load like lights, brakes does the same thing. As you drive it doesn't matter as much, but it hurts more in stop and go traffic. I dont use the air conditioner that much, because I am used to being in a hot environment, like 120 or higher degree trailer. I also noticed that more fuel is burned when the alt. is charging the battery, when I get off the highway it's charging at 12 volts not 14 when I started it. That one reason cars get bad mileage in the winter, heater on and engine burns more fuel to maintain heat and lights are on so the alt. is always charging. wipers on etc. Defrosters is the same as having the ac on but it cycles.

 

I never paid attention. What ever it's costing me for the comfort I gain having the a/c on I couldn't care less.

 

I agree living in that heat mpg doesn't matter that much, but I do not drive my car during the high heat of the day but if I did I would use the ac more.

 

go with the 50/50 rule..

under 50mph windows down, a/c off.

over 50mph windows up, a/c on.

The windows down over 50mph starts producing a lot of drag which will hinder your mileage.

 

I know this is neither the answer nor the question the OP wants.

But for me? I don't worry too much about the fuel cost of running the air conditioning. Honestly, I never have, but especially with a Black vehicle? Absorbing the heat during the summer? I just use the tool for the purpose it was designed, and when I need it? I need it. The "Eco" choice I make is just determining when I need it, and if I can get away with not using the airconditioning and be comfortable? Then I make that choice.

This may seem like a stupid question, but I'm going to ask anyway. Does fan setting have anything to do (or much to do) with how much load your air conditioner is putting on your system? I mean is using the air conditioning at a lower fan speed going to improve your potential MPG's? Or as I would guess, it really has no impact, or little impact. Seems to me the condensor is going to work basicly in the same manner regardless of what speed I set my fan to circulate the air. I also can't think that my "fan" is a big load. So my speculation is that when I'm using my air conditioning it is simply best to use it at the highest fan setting and get as cool as possible, as fast as possible...then just adjust fan speed to maintain. Should this make a difference? Also I always use the air conditioning during the summer with the tempature dial as far over in the blue "cool" as possible. Since we aren't offered a thermostat like setting I'm thinking no benefit in turning it down.

 

I've always wondered that myself.. hopefully someone that knows chimes in.

I usually only use my a/c in the oppressive summer afternoons as the mornings and nights aren't that bad.. at least for me (i've grown use to FL's heat & humidity)

 

The fan is just the fan. What it will do is put an 'extra load' on the AC by drawing more air through the evaporator core at higher speeds. Is this anything to be concerned with??? I don't think so. I want all the cold I can get.

 

Any time there is a load on the engine lights, fan, the ecu doubles the fuel at idle and more fuel is used through out the powerband so you wont notice a drop in power. When your at highway speeds the mpg lost is less then when accelerating to speed. Also I use the AC to cool motor off because it will allow the engine fan to come on. There might be quicker acceleration if the fan is on low with the AC on normal, because the extra fuel being injected into the engine, idle is also controlled by timing so there is extra torque available too.

 

this Fits in this thread, but it was close to 100 here yesterday and I had the Fit A/C blasting. At work I park in a garage, and turned my lights on. When I got the Fit parked, I turned the lights off, and the fan speed increased (turned it on and off several times after to verify). It seems weird that charging system would be that weak that turning on the lights would affect it so much. Is this fixed with the grounding strap that people talk about in other threads, or is this unique to my car?

 

Typical. Not to worry it does it's job. Some say it is quite sufficient..?.. Try searching the forum - I'm still trying to get that down. Search 'Posts' and breeze through, quicker for me.

There are a few threads out there. A summer topic I'm guessing. Like Fall Fashion - look for anti-freeze/coolant questions soon..LOL.

Not sure on the grounding strap, pretty sure not.

 

Ground straps wont help unless your have a stereo system. If ground straps are bad your car wont start or run. You can use a smaller pulley to spin alternator faster to charge battery faster if its a problem.

 

I've noticed in summer I get about 2-3mpg less. I use the A/C, and that has a lot to do with it I would imagine, but something else to keep in mind is that depending on where you live your summer fuel may be oxygenated. This results in less energy / liter of gas, which means you need to burn a little more to go just as far. Further, the air is hotter and therefore less dense, so you're taking in less air into the combustion chamber, with weaker gas. This may result in a decrease in mileage as well, at least I theorize it does.

Regarding the question in this thread about fan settings, and A/C, I would imagine that setting the fan on "4" (full on) would decrease mileage more than setting it on "1", all things being equal. You're not losing tons of energy in the increased demand on the fan motor, you're right Krimson, however you are increasing the load on the compressor. Modern A/C compressors on cars have clutches, and cycle on/off depending on the temperature of the coils. The coils are kept at a certain temperature, and by passing more air over the coils (increasing the circ fan speed) you'll require that the compressor cycle on more than off, thereby increasing parasitic draw on the motor. My $0.02.

 

2.5 MPG less w a/c on in town

 

casual observation: seems I get 1-2 mpg less during summer months with A/C running, tank for tank, over the same semi-urban commute.

 

My mileage with AC on is closer to 4-5 mpg less. Mostly highway 26 miles one way to work with about 4 mile of semi city driving.

 

AC doesn't affect my mileage due to the way I drive. At a stop light I'll turn the AC off. On local roads under 40mph, unless it's really hot outside I won't run the AC. I'll turn on the AC on the freeways when I'm cruising, but if there's an uphill incline I turn it off to feed all of the power to the engine.

 

Point well taken - thanks.

Past three days it's been hitting 95F+ here in good old up-state NY and I'm running at max parasitic draw_

Still @ 38+MPG on the tank I've got running. I couldn't imagine the AC is having that much effect on my driving profile. If it does, so be it.

K_C_Needs to be_

 

Thats good mpg, are you still experimenting with gasolines?

 

On my third tank of premium. Looking good, but I'm not sure it's the fuel - more simple old technique me thinks. I'll soon go back to regular and catch a look-see before the season changes. Right now I'm not thinking premium is cost effective from the MPG point of view.