Wordpress version for this autocomplete jQuery code

The following code works well but does not work in wordpress please assist:

$(document).ready(function () {
var ac_config = {
    source: "ajax.php",
    select: function (event, ui) {
        $("#facility_name").val(ui.item.facility_name);

    },
    minLength: 1
};
$("#facility_name").autocomplete(ac_config);

});

The problem is that the ajax.php is file is not being seen as the source. Can someone help with correctly declaring the source?