Is it better to leave the AC on at all times?

True or False: Is it better to leave A/C on all the time using as needed than turning on ONLY when needed?

I don’ see any benefit to leaving it on all the time. But where I live it is on 95% of the time.

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Ruth , your vehicle should have auto temperature . So just set the temperature to where you want it and the car will do the rest. Also the ac will also help during cold weather to keep your interior windows clear.

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Agree, put the climate control in ‘automatic’ mode, set the temperature you like, and enjoy.

An added advantage of leaving the climate control on all the time is that you will get better gas mileage at higher speeds. This is a benefit on surface streets at 40mph and higher in addition to highways.

I beg to question your answer. The power to operate the A/C has to come from somewhere and that is the engine. Every time you run the A/C at high or low speed fuel consumption will increase.

If you drive with the windows up you are correct, if you lower the windows even a little bit, the aerodynamics change and the retards the cars motion forward more.

An AC compressor draws as much as 5-6 H.P. from the engine.

That will reduce fuel mileage.


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The concept is driving with the windows closed, thereby improving aerodynamics, will compensate for compressor power requirements.

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And the OP’s concept of worrying about the tiny mpg hit that might result to a Mercedes E-class boggles my mind…

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When I get too warm, I turn the air conditioner on. When it’s too cold I turn it off. Driving with the windows down though can ruin your hearing. That’s why a lot of truckers have hearing loss in their left ears. Not to mention junk on the road being thrown at you through an open window.

It would be nice if Ruth posted back with the thoughts that generated her question.

It’s tough to run with the A/C on up North during the winter!

The a/c is typically on when the front window defroster is on.


I feel like I remember @Tester mentioning that they run the A/C when they start their cars in the cold Minnesota winter because the A/C air is warmer than the ambient air!

This is a moot point with automatic climate control. Set it and forget it.

The a/c compressor won’t run when it is below a certain temperature.

Since Ruth never replied back, my guess she did not care about an explanation, so I will give her answer to her True or False: Yes

Like so many others since that ill-conceived Ask Someone feature was added.

False. You won’t hurt anything by turning the air conditioner off. You also won’t hurt anything by leaving it on all the time. Run it when you’re too hot, or when the windows fog up. If you’re too cold, it’s just fine to turn it off.