I’m driving 60 mph, it’s 100 degrees outside and I have the A/C on. Is it more cost effective to turn the A/C on “typhoon” for a bit, then off, or set it to “ocean breeze” and leave it there? Or set it to “typhoon” and leave it there? Or what? Let’s forget the safety issue for now, OK?
Its most likely to make no difference at all - or at least a difference so small that it would be imperceptible. (Isn’t there something between “typhoon” and “ocean breeze?” You could always use that just to help you stop thinking about it).
Were you referring to fan speed or temperature setting?
What type of car do you own?
If you are referring to the fan speed, then I can tell you that there is absolutely no difference in fuel mileage between “typhoon” and “ocean breeze”. If you are referring to the temperature setting, there is also likely no difference in gas mileage if it is a modern car.
Years ago, A/C compressors cycled on and off at a rate that was dependent on the A/C temperature that was selected. However, nowadays, every A/C that I am familiar with keeps the compressor running at the same rate, regardless of temperature setting and controls the temperature of the output air by blending it with a bit of heated air when less than maximum cooling is selected.
It is possible that some very low-end cars still cycle the compressor depending on temperature setting, and if you have one of those cars, then a higher cabin temperature would go hand-in-hand with less run-time of the compressor–in which case you might see a very minute increase in gas mileage by upping the temperature setting, i.e. perhaps an increase of…4/10 of a mile per gallon. In other words, not enough of a difference to warrant being uncomfortable.
It won’t matter where you set the fan speed. The AC compressor cycles on and off to maintain the correct refrigerant pressure in the system. The fan speed has nothing to do with the load on the engine.
Set the AC controls for comfort and don’t worry about the minor details.
Before you ask, it’s more efficient to operate the AC with the windows closed than it is to turn off the AC and fight the aerodynamic drag from open windows.
What safety issue? What do you mean by cost effective?