Does Using Air Conditioning on Highways Consume More Fuel?
3 Answers
Highway driving with air conditioning has minimal impact on fuel consumption. While using air conditioning inevitably consumes more fuel, generally, car configurations mainly include manual and automatic air conditioning systems. Manual air conditioning systems typically use a fixed-displacement compressor, where adjusting the fan speed has no effect on the compressor. Once the air conditioning is turned on for cooling, the compressor operates at full speed continuously, so there is no concept of fuel-saving or not. More details are as follows: Note 1: Adjusting the temperature in manual air conditioning merely mixes varying amounts of hot air with the cold air. In practical use, the cabin temperature rarely reaches conditions that would stop the compressor. Simply put, this type of fixed-displacement compressor runs at full speed once activated and does not shut off; thus, even if the temperature is set higher, it does not save fuel. Note 2: Automatic air conditioning can also use fixed-displacement compressors, operating on the same principle as manual systems but with an added automatic temperature control feature. It automatically selects between "pure cold air" or "mixed cold and hot air" based on the difference between the cabin temperature and the set temperature and adjusts the fan speed accordingly. Therefore, the set temperature has no relation to fuel efficiency—using air conditioning will always consume more fuel.
After driving for over 20 years, I've found that running the air conditioning on the highway does indeed consume more fuel. The AC compressor requires the engine to drive it, which means the engine has to work harder and burn more fuel. For example, when cruising on the highway at 120 km/h, the normal fuel consumption might be 8 liters per 100 kilometers, but with the AC on, it could rise to 8.5 or even 9 liters. This is because the AC load increases the engine's workload by 10-15%. It's advisable to adjust the temperature settings appropriately—not too cold—to reduce fuel consumption slightly. Additionally, maintaining a steady speed and avoiding sudden acceleration or opening windows at high speeds (which increases air resistance) can help. Overall, comfort is important, but small fuel-saving tips like regularly cleaning the AC filter can also make a difference. I always test these methods on long trips and can usually save a few bucks on average.
As someone who enjoys studying cars, I've given this some thought. Turning on the AC will definitely increase fuel consumption because the compressor draws power from the engine, increasing mechanical losses. At highway speeds, while aerodynamic drag is reduced, the impact of AC remains noticeable—fuel consumption rises by about 5-10%. It's advisable not to use the cooling mode for too long; setting it to 25-26°C is sufficient. Additionally, using the fan to assist in cooling can reduce the frequency of compressor activation. Regularly checking tire pressure can improve overall efficiency and reduce extra fuel consumption. Having tested different car models, I've found that smaller displacement engines are more affected by AC usage, so considering powertrain configuration when choosing a car is also crucial.
