Depending on the size of the car and type of journey, fuel use should be between five per cent and 10 per cent.

The worst fuel economy will be over short trips (with the AC on max) with the windows shut - this will force the engine to work harder to power the system and cool the interior.

The most efficient way to cool your car is to power the AC slowly with air vents directed to the footwell and all of the windows open by one-third (assuming your car has fully powered windows). This will cool the car more gradually and allow the hot air to escape. If the interior doesn't cool after 10 or 15 minutes then get it inspected by an automotive AC specialist.