How much fuel does a car consume when idling with the AC on for one hour?
3 Answers
When a car idles with the AC on, it consumes approximately 1 liter of fuel per hour. There are many hazards associated with idling with the AC on. Idling with the AC on damages the car: Idling with the AC on causes incomplete combustion in the engine, increasing carbon deposits inside the engine. If the AC is left on while idling for an extended period, people inside the car may also experience carbon monoxide poisoning, which is very dangerous. Idling with the AC on can lead to incomplete fuel combustion: When a car idles (vehicle parked without pressing the accelerator), the fuel reacts with oxygen in the air but burns incompletely, producing more exhaust gases containing carbon monoxide. To save energy, drivers often close all windows and doors after turning on the AC.
Idling a car with the air conditioning on for one hour consumes approximately 0.8 to 1.2 liters of fuel, depending on your vehicle's engine displacement. The engine inherently burns fuel during low-speed idling because the pistons require power to keep operating. When the air conditioning is turned on, the compressor activates, increasing the engine load. Consequently, the engine must output more power to drive the compressor, naturally leading to higher fuel consumption. For example, a small-displacement 1.5L car might use only about 0.6 liters per hour when idling without air conditioning, but fuel consumption can rise to nearly 1 liter once the AC compressor is engaged. This phenomenon is quite common—I've tested it several times myself, and a noticeable drop can be observed on the fuel gauge. Over time, prolonged idling also accelerates engine carbon buildup and component wear. That's why I often remind friends that turning off the engine while waiting is more cost-effective, saving fuel and protecting the car.
My compact car has a 1.2-liter engine. One summer, I idled with the AC on in a parking lot for about an hour during hot weather, and the fuel gauge noticeably dropped. I estimated it consumed just over 1 liter of fuel—engine idling already consumes energy, and turning on the AC immediately puts extra load on the engine, reducing efficiency. Most people would feel the pinch of wasted fuel costs, especially when gas prices are high. Now, when waiting outdoors, I try to park in the shade, turn off the engine, and roll down the windows for ventilation to stay cool. If I do need the AC, I only run it briefly—within minutes, you can feel the temperature change, so there's no need for prolonged idling. These daily habits have saved me a lot of expenses and hassle.
