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ambush
By ambush | AA Member | 2 Posts | 4 September 2011 at 5:33pm

Hi, Was wondering whether it is more fuel efficient to drive with the window open to cool down, in the car, or turn on the airconditioning. Have heard conflicting answers in the past, so thought I'd find out the truth from an expert!!

markstockdale
By markstockdale | AA Expert | 101 Posts | 7 September 2011 at 8:55am

Its better to use your air conditioning than have your windows down. AA tests show that having your windows down and gear on a roof rack causes extra drag and can increase fuel consumption by 11%, while air conditioning can increase consumption by 9%. But at low speeds around town, having your windows down will make little difference to fuel consumption but consider that air con filters the air so you won't be breathing in fumes and it will make you more comfortable than relying on the ambient temperature.

See also this blog entry.

ambush
By ambush | AA Member | 2 Posts | 7 September 2011 at 9:02am

Hi Thanks for that. However we don't have a roof rack, so do you have figures on the fuel consumption of just having the windows down? Alos, just 2 windows. Don't usually drive with all 4 down. Hope you can help.

markstockdale
By markstockdale | AA Expert | 101 Posts | 7 September 2011 at 11:04am

I don't have an exact figure, but overseas experts say having your windows down at open road speeds uses more fuel than air conditioning. Even one open window will create a lot of drag. Our advice would be to use air con instead of open windows, but to use the air con only when necessary.

yahzoo7
By yahzoo7 | AA Member | 1 Post | 7 September 2011 at 11:15am

Just wondering when or how often should the air conditioning be checked? Is it usually checked when you have your car serviced or do you ask as an extra

markstockdale
By markstockdale | AA Expert | 101 Posts | 8 September 2011 at 8:45am

As a general rule around 40K would be the time to at least have a look at the air conditioning filter but a lot depends on the environment a vehicle is being driven in.

Some say filters should be changed every 12 months but we're not convinced it should be automatically replaced simply based on a time period.

For many older cars and those no longer serviced by the franchise network, it is a service item that is totally overlooked in many cases. Often its only when there is a smell in the car that a search for a filter is undertaken.

Not every car has a pollen filter fitted either which can make life difficult for those who work on all makes/models.

For those who suffer badly from allergies then replacement becomes a much higher priority.