A/c running= less mpg?



does running your a/c actually consume more fuel?

I have heard it may be a myth/old tale…

i do knowtice a small difference on the acceleration …

some say no while others say yes…

Whats your take on this?..



Yes, and maybe no. Running the AC definitely puts more load on the engine and therefor definitely uses more fuel. However, if you turn off the AC and open the windows the extra drag created by that may well use as much or more fuel. This will vary from car to car because the aerodynamics will vary. The AC doesn’t use very much extra fuel and in my opinion it’s a foolish way to try to save fuel by killing yourself with heat and wind noise.


i kinda figured that its a lesser evil of the 2 to run your air instead of opening windows in 100 degree day even if drag is not a case if your bumper to bumper…


Some cars actually run the compressor any time you have the fan running until it drops to around 35 degrees outside. It may be on with every setting (defrost, heat, vent, etc.)but that varies with each car. I had a ford car on which the a/c compressor cycled on and off even when I had the heater or defrost on. Only went off when I had the vent setting. I was told it was to dehumidify the air to prevent fogging on the windows. So leaving it on with the windows closed may not make a difference if you have that kind of car. You can tell if yours does this from the owners manual.


i don’t know where the manual is but i think my car being a 98’ saturn , does not have it on all the time as i do knowtice and hear the compressor kicking in when i turn the a/c on. but i do knowtice in winter when i turn on the defroster the windshield gets clear of fog very fast as if the compressor would be on…hmmm?


The answer is: At low speeds <35mph, it takes more fuel to use the A/C since wind resistance from windows down would be relatively low. Above 35mph, putting windows up and turning A/C on uses less fuel. This has been proven in tests I’ve seen. The compressor comes on when you use either the “defrost” or the A/C setting, but not with the “heat” setting.