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Air Conditioning Question

Does anyone know which option uses less gas? For the record, I drive a 2000 Honda Accord, and I have 2 AC knobs - one that controls temperature (ranging from all the way blue [cold] to all the way hot [red]) and one that controls fan speed (1-4):



1. Temperature all the way cold, fan speed all the way low (1)

2. Temperature slightly cold, fan speed moderate (2-3)



Both of these provide comparable levels of comfort for me, and I’m curious which one uses less gas. Anyone know for sure?

They should be about equal. One thing that will increase mileage ever so slightly is to switch to recirculate instead of fresh air. The more humid the area you live in, the more that this might save, however, it will probably be undetectable.

Fan speed and temperature setting don’t have any impact on fuel mileage. The AC compressor cycles on and off to maintain the correct pressure within the AC system. Where you set the controls doesn’t matter.

From a gas mileage standpoint the only thing that matters is AC on or AC off.

From a gas mileage standpoint the only thing that matters is AC on or AC off.

And if you turn it off and open the windows, you likely will get lower mileage. I will vary from car to car. Overall the differences are too small to worry about.

Small, high efficiency cars, mostly 4 cylinder models, suffer a much higher mileage penalty when air conditioning is used…How you adjust the control’s makes almost no difference.

If there is any difference, and I really doubt you could measure one, I would think low fan speed with temp setting all the way cold would be better. Here is my reasoning: The AC just tries to maintain the correct pressure differential at the pump. When you turn the temperature dial up it uses warm air from the heater core to mix with the cold air from the AC evaporator. This might make the pump run a bit longer because now it’s fighting the slight load of cooling warmer air. I really think the difference will be minuscule and not worth worrying about.

Here is AZ if you do anything but turn the temp to max cold and the blower to max high there could be a lynching. Really the only thing disputed is how long to leave the windows down to blow out all the hot interior air. Some say 5 seconds other say 30 seconds anything over 45,you have the same potential for a lynching.

Gas use is the lowest item on the list when all you want is relief from outside temps of 118F and inside the car temps of 165F.

My answer to the windows down uses more gas club is, leave the AC off and the windows up if gas mileage is so important.

A GM instructor told me that a Surburban has the same AC capacity of a 3 bedroom house. The AC system has a really tough job,it is a wonder that compressors work as good or last as long as they do.

When speaking of load placed on the engine by an AC compressor, make sure your brain is in 2010 mode and not thinking of the 60’s when AC compressors were real hogs to get turning.

It’s more important that you are comfortable than worry about the gas used by the air which is minimal. The most problems I’ve seen with car air systems, are with people that do not use them regularly which is where the big expense comes in. They are made to run with sustained lubrication. Don’t worry about it. It’s an irrelevant discussion in the modern sedan.
Sorry…I’m NOT that curious.

I agree with Ranck’s comment. The more heat energy is removed via the evaporator is the more work the compressor will have to do. Pressure differences within the system are, after all, affected by the temperatures of the refrigerant.

But you’d need on heck of a serious lab setup to prove the theory. The difference to you in your car would be unmeasurable.