Is it more fuel-efficient to use the internal or external air circulation?

[LawsonRose]

Using the internal air circulation is more fuel-efficient than the external air circulation. Here are the relevant details: External air circulation: External air circulation refers to drawing air from outside the vehicle, directing it to the air conditioning system for heating or cooling, and then blowing it out through the vents. External circulation can replenish fresh air and improve the air quality inside the vehicle. However, if the weather outside is extremely dry and hot, using external circulation requires the air conditioning compressor to work continuously to cool the hot air from outside, which consumes a certain amount of fuel. Internal air circulation: Internal air circulation involves recirculating the air inside the vehicle. The air conditioning system draws in the interior air, cools it, and then returns it to the cabin. Once the interior temperature drops to the set value, the air conditioning compressor stops working, reducing the engine load. Therefore, the faster the interior temperature reaches the set value, the sooner the engine load is reduced, leading to lower fuel consumption.

[VonEmma]

Using the car's air conditioning in recirculation mode generally saves more fuel. I discovered this from my own driving experience. During summer traffic jams in high temperatures, turning on the recirculation mode allows the system to circulate air directly from the cabin, eliminating the need to heat or cool outside air, thereby reducing the load on the AC compressor. Since the compressor is driven by the engine, fuel consumption naturally decreases. In winter, recirculation also helps retain warm air inside the cabin. However, prolonged use of recirculation can make the air stuffy, so I often switch to fresh air mode for a few minutes to ventilate. Although fresh air mode introduces outside air, it requires the system to handle external temperature changes, especially in polluted urban areas or during high-speed driving with strong winds, making the AC work harder. Overall, to minimize fuel consumption, I use recirculation more often and switch to fresh air mode only briefly when air quality is good. After adopting this habit, I noticed a slight reduction in fuel costs per 100 kilometers.

[MarcusRose]

From a fuel-saving perspective, using the recirculation mode is more efficient than the fresh air mode. The reason lies in how the air conditioning system operates: recirculation mode minimizes the intake of outside air. Since external air requires heating or cooling, this increases the compressor's workload. The compressor is powered by the engine, meaning the engine consumes more fuel to maintain cooling performance. Recirculation mode bypasses this step, thereby improving fuel efficiency. This is particularly noticeable during hot weather when high external temperatures trigger frequent air conditioning cycles to cool incoming air, placing greater strain on the engine. Conversely, in cold climates, recirculation mode also conserves thermal energy for the heating system. However, prolonged use without fresh air mode may lead to oxygen depletion or odor accumulation inside the cabin, so I periodically switch to fresh air mode briefly for ventilation. Overall calculations show that recirculation mode helps me save approximately 5% in fuel consumption.

[MariaLee]

Using the recirculation mode saves more fuel. I've learned that when the air conditioning is operating, the recirculation mode circulates air directly from inside the car without needing to process fresh air from outside. Processing new air requires energy to heat or cool it, which increases the engine's load and consequently consumes more fuel. While the fresh air mode improves air quality by bringing in outside air, it is slightly less fuel-efficient. The difference is particularly noticeable during extremely hot or cold seasons. Occasionally switching to fresh air mode is fine, but keeping the recirculation mode on for extended periods can save fuel.

[VonFinley]

Using recirculation mode is generally more fuel-efficient. For the air conditioning system, recirculation means not drawing in outside air, which reduces the additional workload on the compressor. The compressor operates via the engine, so lower load means less fuel consumption. Using fresh air mode requires handling external temperature and humidity changes—for example, strong cooling is needed against summer heatwaves, which wastes more fuel. Recirculation significantly improves efficiency during urban traffic jams. Only use fresh air mode for ventilation during long trips or when outside air is fresh. Remember this fuel-saving tip: use recirculation more and fresh air mode less.