Start the car place heater control dial in the floor position as shown. Air conditioner light on the button will NOT come on...OK have some one watch the clutch on the air conditioner compressor. YEP your aircon is running. So on cold days when you have the heater control on in the floor position your airconditioner will be running using up fuel and you won't know it. Unless you turn the other knob to cold and you feel chilled air....
This is why people report water leaks in the winter they can't understand, its the bloody condensation over flow from the aircon....