Does using an air conditioner affect fuel consumption?

I have always understood that running the air conditioner causes an increase in fuel consumption. Last week, in very cold weather, I was taken for a demonstration drive in a new Toyota Avensis. The dealer kept the air con on all the time. When I queried this practice he said it makes hardly any difference to the MPG figures. Is he right?

Asked on 2 February 2013 by JM, Prestbury

Answered by Honest John

Yes. In summer the a/c uses more fuel than opening the windows up to about 40mph. Over 40mph the extra drag caused by opening the windows uses more fuel than the a/c. In the situation you describe, the a/c probably needed to be on to dry the air in the car and keep the windows clear. If a car has a/c it’s best be run for 10 minutes every week right through the winter, in order to keep the system's seals lubricated and gas-tight.

Tags: air con fuel economy

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