How much does your A/C affect your gas economy?

You will use about 10% more gas with the A/C on. How much more will vary depending on the outside temperature and how cold you want the car to be inside.

Your A/C is either on or off, the compressor that is…

Turning the thermo up or down simply determines how frequently and how long it remains on or off.

@Photosopher I’m referring to a vehicle A/C… the kind that is either on or off… not set by a thermostat to reach a certain temperature.

Well that’s what the temperature control in your car does too. Same principle.

I once wired my Subaru with a separate A/C compressor switch under the dash, allowing me to turn it on or off at will, rather than wait for the thermostat to kick it on or off. It was cheaper to do that than replace the broken thermostat.

I get a few miles less per gallon in the hot weather but we have over 100 degree days so the inside to outside difference is huge.

Yes, it uses more gas. However, rolling the windows down creates a drag, forcing the car to use almost as much the same amount of gas as it would with the AC on, windows up, and no drag.

Highway speed with window up, 10 to 15 percent. With no A/C.
@Photosopher I can shut off the compressor.

Newer cars are designed to get better mileage with the windows up and the A/C on. Rather than having the windows down and traveling at Highway speeds.
Plus the modern compressors are much more efficient than the those from a couple of decades ago. Not to mention the cooling systems are better, which let’s you have the air on in stop and go traffic with little or no harm to the engine.
The fuel economy gain loss is almost negligible. It’s your right foot that determines the cars actual mileage.

Using A/C burns more fuel BUT except for the window comparison that many guys here said and is correct there is also something else very important to remember.
Using A/C when going fast-high revs makes almost no difference in fuel consumption.
Using A/C when going slow 1st-2nd-3rd gear and such speeds makes a big difference in fuel consumption.
So Remember…use A/C when on highway but do not use A/C when in city

Hypermilers do not use a/c for better efficiency. We notice at least a 10% decrease in efficiency when using a/c with out Prius.

You will loss about 10% to 15% more gas. because to turn the air conditioner pump The motor needs to function harder . At the same time when you run the defroster to clear the windshield you are additionally utilizing the air conditioner to uproot moistness buzzing around. Generally drivers don’t know this and waste energy unknowingly by keeping defroster on.

On the interstate or when driving at higher speeds, the airflow into the car with the windows down hurts gas mileage. Therefore, windows down in town, and a/c up on the interstate.