function normal() {
  $('#on').attr("src", "medias/images/on.jpg");
  $('#air').attr("src", "medias/images/air.jpg");
}

function clignoter() {
  $('#on').attr("src", "medias/images/on_rouge.jpg");
  $('#air').attr("src", "medias/images/air_rouge.jpg");
  window.setTimeout(normal, 2000);
}

$(document).everyTime(5000, function() {
  clignoter();
});