Is it true that air-conditioning wrecks fuel economy?

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Car Clinic: Ford Focus air conditioning

Q. My garage tells me I should use my 14-year-old Ford Focus’s air-conditioning regularly in order to keep it functioning. I rarely turn it on as I’ve been told it wrecks fuel economy, but the garage insists that it doesn’t use much more fuel. Who’s right?PD, Hornchurch, London

A. Your garage is correct. Air- conditioning “wasting” fuel is a popular topic for the kind of people who like to badger you about the irresponsibility of using a car at all when you could be standing in the rain waiting for a bus.

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As with any machinery, an air-con that is left unused for months on end risks having components seize up, so run it regularly during the winter: the circulating coolant fluid will help keep the moving parts lubricated and the seals intact. Since at this time of year the car will already be cool, you will not need to do much more than move the fluid round the system.

Air-conditioning relies on a compressor driven by the engine, and the radiator fan and heater blower will run continuously while it is turned on, so it will burn some extra fuel. But as 10 minutes’ use every few weeks is all that’s needed in cold weather the cost is negligible.

Obviously it takes more energy to run the air-con in warmer weather when use of the system can make a dent in fuel consumption if you’re doing lots of short trips. On long journeys, though, the difference will be hardly noticeable (because once the car is cool, keeping it that way burns much less fuel).

And let’s face it, even a 10% penalty is hardly wrecking the car’s fuel economy — an efficient driving style and keeping the tyres properly inflated will easily save more than this.

A good tip, come the hot weather, is to drive with the windows down for a few minutes to clear the hot air from the cabin, then close them and turn on the air-con.
Sunday Times Driving car clinic expert: Tim Shallcross

Tim Shallcross used to train AA patrols to fix cars. Now he advises the Institute of Advanced Motoring – read more from Tim here.

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