Return a PartialView from $.Ajax Post

I have the following code;

        $.ajax({
            url: "/Home/jQueryAddComment",
            type: "POST",
            dataType: "json",
            data: json,
            contentType: 'application/json; charset=utf-8',
            success: function(data){ 
                //var message = data.Message; 
                alert(data);
                $('.CommentSection').html(data);
            }

And in my controller;

    [ValidateInput(false)]
    public ActionResult jQueryAddComment(Comment comment)
    {
        CommentSection commentSection = new CommentSection();

        //ya da - ya da 
        // fill the commentsection object with data

        //then
        return PartialView("CommentSection", commentSection);

    }

However, when I get back to the page the success alert doesn't happen. Can anyone see the flaw in this logic?