How does using the AC affect a car’s mileage while driving? Premium

Learn how an air-conditioner affects a car's mileage and engine load, and tips to improve fuel efficiency.

A: An air-conditioner (AC) works by moving heat from an ‘inside’ space to ‘outside’. It achieves this using a refrigerant, a substance that absorbs heat when exposed to the ‘inside’ and releases it when exposed to the ‘outside’. The refrigerant needs to be pressurised before it can absorb heat, which is achieved using a compressor.

In a traditional (non-electric) car, the energy to run the compressor comes from the engine. That is, the AC is another load on the engine aside from running the car itself. As a result, the engine consumes more fuel, but not all the fuel contributes to moving the car: some goes to running the AC. And as a result, the number of kilometres to which a single litre of petrol contributes – a.k.a. the mileage – drops.

The effect of an operating AC on the mileage also varies by the driving conditions. For example, driving within a city forces the engine to stop and start multiple times during a trip whereas on a highway the engine operates more continuously. In this scenario an AC’s effect on the engine, and the mileage, will be more pronounced in the former and less so in the latter. Drivers can also reduce the load on the engine by parking cars in shaded spots and pre-cooling the passenger area through other means before turning the AC on.

The Hindu S&T Desk