I think that you are talking about the three vertically stacked switches above the radio.

If so, when the red light is on that means the function is engaged;

Top one is Rear Window Defroster.

Middle one is to engage A/C compressor.

Bottom one is to turn on/off air re-circulation; when the red light is on, that means that you are NOT taking in fresh air - you are re-circulating the cabins air.