Most cars have a simple button for turning the air conditioning system on or off.
Some cars however have a button which frequently confuses the owner and is responsible for some of the reports we receive of poor cooling. It shouldn't really - we are all supposed to read the drivers handbook to understand how to operate all of the complicated systems within the modern car - but who does? In these busy lives we lead who has time to plough through 100 pages or more of complicated instructions, often poorly written, frequently with large sections that do not apply to the model we have just purchased but which is not immediately apparent. It's not a surprise therefore that this document spends most of it's life in the glove pocket and is only opened when a fuse has blown and needs replacing.
If your car does not have a simple button decorated with a snowflake symbol which alternately turns the aircon ON and OFF then read on. You may have a Mercedes who assume that if you can afford a brand new Mercedes then you will always want the benefits of air conditioning turned on at all times. Not all of us buy brand new cars though and even I will occasionally find times when the use of AC is unnecessary. At this time in a Mercedes you will need to press the buttom marked "EC" and the light within it will come on to remind you that the air conditioning has been turned off. Unfortunately many Mercedes owners are under the mistaken impression that "EC" is the German abreviation for Air Conditioning. It is not - I suppose that that would be KL. But when they think that they have just turned the AC on they have actually turned the AC off. What "EC" stand for is ECONOMY. In most cars ECONOMY or ECON or EC means that the Air Conditioning is turned OFF. On a very few cars ECON will simply reduce the amount of AC being provided to a minimum but not actually turn it completely off but in the vast majority of cars it TURNS THE AC COMPLETELY OFF.
Volvo takes a different tack. They use a button prominantly marked "AC OFF". Now that's clear isn't it, so why does it cause so many problems? When the button is pressed the light comes ON and when it is pressed again the light goes OFF. Perhaps we Brits are not as logical as the Swedes but there are so many people, too many for it to be a coincidence, who then assume that when the light is ON so is the AC ON - WRONG!!! When the light is ON the button is activated and don't forget this button is labelled "AC OFF".
One final point - if you find that one day that the ECON button is illuminated but you have never pressed it then the light might well be showing a fault with the system, possibly just low on refrigerant. So if it is impossible to extinguish the light, get it looked at by a specialist. With some cars, even after curing the original fault the light will remain ON and the AC will be inoperable until the fault code is removed by an Electronic Diagnostic Console.