[cflsystems]

Not tested, make sure you backup the file first:

you can try this - open include/search.tpl, find

   default:
    $sort_string = "$sql_tbl[products].product";

and replace with

   default:
    $sort_string = "$sql_tbl[products].add_date $direction";

Just below it find

else {
  $sort_string = "$sql_tbl[products].product";
 }

and replace with

else {
  $sort_string = "$sql_tbl[products].add_date DESC";
 }