How Much Fuel Does Air Conditioning Use?

Because of our usually mild summers, you might find you don’t often use the air conditioning in your car. However, during those rare heatwaves, air conditioning can be really important to help to keep you cool and comfortable. You might have heard that having the windows down can decrease fuel efficiency, but have you ever stopped to wonder how much fuel your car’s air conditioning could be using?

Does Using Your Air Con Use Petrol?

The way in which your car’s air conditioning system works means that some energy is required to carry the cool gas into the cabin of your car.

Within this system, a compressor contains a refrigerant, just like your fridge. As fresh air enters the system, the refrigerant causes the temperature of the air to drop considerably. At this point, the refrigerant turns into a liquid and any impurities are removed. The liquid reaches a thermal expansion valve where the liquid flow can be limited. This gives you control over the internal temperature of the car. Finally, the liquid is turned into vapour where it can travel through evaporation coils to be blown through the vents as nicely chilled air. The refrigerant returns to a gas and the whole process can be repeated again to provide constant cool air.

The compressor requires energy to run your vehicle’s air conditioning system and so will use a small amount of fuel whenever the system is running. It could increase your fuel usage by as much as 10 per cent, and the effects are particularly noticeable on short journeys.

When you initially set off, the air con has to work hard to bring the internal temperature down to a comfortable level. However, once the car has cooled enough, you can choose to reduce the flow rate, increase the temperature or turn the air con off altogether. On a long journey, it’s unlikely that the air con will need to be blasting the whole way. This is why increased fuel consumption caused by using your air con may be more noticeable on a short journey.

How to Save Fuel When Driving

There are a number of ways that you can save fuel while driving, including accelerating and braking slowly and smoothly, keeping to speed limits and ensuring your tyre pressure is correct for your tyres. These are a few of the most common sensical ways that probably won’t make much difference to your journeys. However, there are some less obvious steps you can take too, including keeping the radio off and limiting the weight in your vehicle.

If you’re worried about your air conditioning using precious fuel, there are some ways you can reduce its consumption. When you first set off on a journey, it’s better to open the windows for a few minutes. Doing so will remove the majority of the hot air in the cabin and therefore your air conditioning won’t need to work quite as hard.

Despite what many people think, driving with your windows open isn’t so bad on fuel when you’re going at slow speeds. Therefore, if you’re driving through towns and cities, opening your windows will save more fuel than using the air con. If you’re driving on fast roads, it is more beneficial to use the air con as the additional drag caused by open windows could use additional fuel.

Once your car has cooled down enough, the air con flow rate can be reduced so that less air is allowed into the cabin or you could slightly increase the temperature. Both of these things will mean that the compressor doesn’t have to work quite so hard. Of course, in terms of fuel usage, it’s most beneficial to drive with no air conditioning and your windows up, but on a hot day, this is probably not possible or desirable.

It’s also important to have your vehicle’s air conditioning system serviced regularly. This should be done every two years to ensure that the system is running efficiently and any lost refrigerant is replaced. When the refrigerant levels drop, the system has to work harder to produce the amount of cool air that you need. This will use more fuel, so it’s a good idea to keep up to date with your air con service to conserve even more petrol.