How does Air conditioning affect mileage in a car?

“Control Panel” by catatronic is licensed under CC BY-SA 2.0

Having an air conditioner in your car was considered a luxury almost 20 years ago. Even houses with air conditioning were limited to the upper class at that time. At least some of us must have traveled in HM Ambassadors with the letters ‘AC’ written in large fonts on the boot, a long time ago. Things have changed dramatically, and cars without air conditioning are almost non-existent. During the majority of the year, temperatures in India remain high, along with a constant increase in fuel prices. Both automakers and end-users are looking for new ways to improve their vehicle’s fuel efficiency while making the most of the air-conditioning system. A car’s air conditioner draws power from the engine, primarily to power the air compressor. A refrigerant circulates through a compressor, condenser, expander, and evaporator, in an air conditioning system, to produce cooling. This is an energy-consuming process and saps power out of your engine. As a result, some fuel used is used by the AC system. In most modern cars, this amount of usage is very small. However, in older vehicles, particularly those with low engine power, running the air conditioner continuously would reduce mileage by a huge margin. This decrease in mileage is exacerbated when such vehicles travel uphill with the AC turned on. This is simply because the engine has to work harder to move the vehicle against gravity.

How much extra fuel or car ac mileage has no specific answer. It is important to note that there is no single answer to this question because a variety of factors are at work. The actual temperature outside, as well as the size of your engine, the make, and model of your car, the condition of your air conditioning system, and many other factors, will all have an impact. However, the US EPA warns that running the air conditioner in extremely hot weather can increase fuel consumption by up to 25% and that using the AC in a hybrid or electric vehicle can have an even greater impact. If you believe that driving with all the windows open is the best way to save fuel, you are mistaken. Driving with all the windows down creates a significant amount of drag inside the car (air enters the car and is blocked by the rear windshield), reducing fuel efficiency even further. At speeds ranging from 96.5 km/h to 112 km/h, driving with the windows down consumes more fuel than driving with the windows closed and the AC running. This will be more noticeable in a truly aerodynamic car, as opposed to a boxcar that has no concept of air movement. 

To summarize, using your car’s air conditioning all the time is preferable to driving with all the windows down. However, if you are traveling at low speeds and the outside air is sufficiently cool, rolling down the windows and driving may provide better car ac mileage. Maintaining your air conditioning system and engine properly will also help you save money on gas. Regular oil changes and clean air filters can significantly improve your fuel economy. It is also critical to ensure that your AC system has the proper level of refrigerant. Also make sure that you set the optimum cabin temperature inside the car, to make the Ac system more efficient. Aim for comfortable, not cold conditions inside the car, this will have a dramatic effect on the fuel efficiency. Make use of your a/c system’s “recirculation” function. This saves energy because you are only cooling the air that is already in your vehicle, rather than bringing in warmer outside air to be cooled. If you park in the shade, your vehicle will require less cooling from the a/c at start-up. If you can’t find a shaded spot, use window shades to keep the heat out of your vehicle while it’s parked. Also, do not use the a/c when starting your vehicle. Instead, open the windows for a few minutes to let the hot air escape. If you follow these practices and maintain all the systems of your car properly, then you can enjoy air conditioning, with a minimum fuel penalty.