On most US cars when you turn on the front window defrosters the air conditioning is automatically engaged. The purpose of this is to dry out the air to help remove condensation better.

The downside of this setup is most people don't realize this and leave their defrosters turned on even when they don't have any condensation or ice on the windshield and drastically reduce their gas mileage. They also put a lot of extra wear and tear on the air conditioning system because it is constantly running.

On most Japanese cars there is a separate on/off switch for the air conditioning. The problem with this setup is that it seems counterintuitive to most people to turn on the air conditioning in the winter when you are trying to defrost your windows.

In a Japanese car you should also set the air control to "Fresh" when you are trying to defrost or defog your windows. If it is set to recirculate the moisture in the air and from your breath will not exit the car and will just condense on the windshield.