There’s a basic understanding among motorists that turning off the air-conditioning in a car will help improve fuel economy. This is not entirely true. There’s more to getting better efficiency out of a car than just that. Here’s what you need to know.

Air-Controls

A car air conditioner filters and cools hot ambient air and throws it into the cabin through the air vents. How it does that is a topic in itself but let’s focus on why it affects fuel efficiency. An air conditioner is made up five parts – a compressor which is the heart of the air conditioner, a condenser, a receiver, an expansion valve and an evaporator, each tasked with various processes using the refrigerant to finally send cool air into the cabin. It all starts with the compressor that is connected via a drive belt to the crankshaft of the engine. This connection increases the load on the engine when the air conditioning is turned on, thus hampering fuel efficiency.

Every time we turn the air conditioning off, we tend to roll the windows down. Rolling the windows down increases drag and so it negates the benefits of turning off the air-con. Getting the best efficiency out of your car isn’t as clear cut as it seems. 

Simple technique for the right balance of AC

Drag is the enemy of efficiency. To reduce drag, we roll the windows up. When the windows are up, the cabin gets stuffy and so we turn the air conditioning on. That consumes fuel and so finding the right balance requires striking a balance between speed and air conditioning. Drag of a vehicle increases as speeds rise. You will notice that the amount of wind gushing into the cabin increases as you go faster and then you tend to roll the windows up just enough to keep circulation in the cabin. To get the best efficiency out of your car, roll the windows up almost till they are shut and drive without the AC turned on. While the drag is reduced, there is also no load of the AC on the engine. This is the ideal setting.

When you are driving in the hills on the other hand, there is a temptation to turn the windows down completely to soak in the weather but that hampers fuel efficiency the most, especially since you aren’t driving in a straight line. Cross winds increase drag further and the engine is under stress anyway due to a hill climb. When you are ambling in city traffic, turning the air conditioning off will definitely boost you fuel economy figure. 

In all conditions mentioned above, fuel efficiency can be improved or maintained by just finding the right balance between turning the air conditioning on or off and rolling the windows up or down.

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