VIEWER SIDE AJAX not working!!!

i really cant figure out why ajax is not working. here is the code I implemented.

for the j-query function (which is loading up corrrectly in my header):

function changeClass()
{
  $j=jQuery.noConflict();

$j.ajax({
			type: "POST",url:"/wp-admin/admin-ajax.php",data:{action:'comment_change_type'},
			success: function(results){
			alert(results);
			}
		});

}

and for my php callback function:

function change_comment_type(){

                echo "OK!";

                die();
}
add_action('wp_ajax_comment_change_type', 'change_comment_type');
add_action('wp_ajax_nopriv_comment_change_type', 'change_comment_type');

any ideas? i am all out of ’em.