A/c Use And Fuel Consumption

[ajfinoak]

If one sets the A/C to cooler temps, does fuel usage go up if the outside temp remains constant?

[Randy&Bonnie]

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[bartkat]

I don't think anyone would try to convince you of that. Of course the A/C compressor takes some power from the engine to run it. In cars with little low powered engines you can really notice the power loss when the A/C kicks in.

Some the loss is offset by better aerodynamics driving at speed with the windows up, but that's a whole nuther argument. ;)

[Randy&Bonnie]

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[bartkat]

I don't think anyone would try to convince you of that. Of course the A/C compressor takes some power from the engine to run it. In cars with little low powered engines you can really notice the power loss when the A/C kicks in.

Some the loss is offset by better aerodynamics driving at speed with the windows up, but that's a whole nuther argument. ;)

So, if you have your AC on and have it set for a lower temperature, the AC pump will be work more, then you will burn more fuel than if you have the AC set for a higher temperature, does that sound right? :D

I think so. The more the compressor runs, the more power it's going to use.

At some point, if the weather is hot enough, the compressor will run 100% and still not be able to bring the temp down to say 70 degrees F. As I understand it, the A/C can only bring the vent temperature down X number of degrees below ambient.

[EnginePassion]

The A/C uses some of the engine power for sure just like if you put some weight in the car. It may not be significat though depending on your set temp and ambient temp and whether you chose to circulate or not. In winter specially in cold areas you use heat to warm the car and that's a load too. Best thing in summer is set your AC to the recirculation mode unless you smoke inside the car.

[lovetoskico]

Part of the reason you may hear that the AC does not decrease fuel economy is due to several factors. One being that the warmer air is less dense that it is during the winter time. Secondly, the fuel mixture provided by many "colder" states is less potent to offset different evaporation rates in the winter vs. the summer. Anyways, there are a number of factors that should decrease your fuel economy during the winter months. Therefore, during the summer running the AC should not make a substantial net difference given you are not running your AC during the winter months to draw out moisture from the cabin.

[Randy&Bonnie]

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[bartkat]

I think he's saying that there are other factors which reduce your winter mileage so your summer mileage with A/C on might be about the same as your winter mileage with A/C off.

What you're looking at is the anytime mileage difference between running A/C on and A/C off under similar ambient conditions.

I expect in Arizona it's similar to here in Alabama. The question is moot because in the summer nobody is going to drive around with the A/C off. It's just too hot. However, in a rather powerful car I don't think the mileage difference is going to be very big, as it might be with a smaller, less powerful engine. As long as there's plenty of power to move the car, the it's not really going to notice the little extra that the A/C uses.

I leave my system in automatic year round and it runs when it needs to and doesn't when it doesn't need to. Same goes for the air recirculating. While some people say it's easier to keep the car cool on recirc, you're really breathing some pretty stale air after while. The only times you need recirc is when initially cooling the cabin and/or when there smoke or dirty air outside that you don't want to enter the car. I find that the auto selection pretty well takes care of that for you.