WordPress Custom Search by post_type

NOT TESTED!

function mySearchFilter($query) {
$post_type = $_GET['type'];
if (!$post_type) {
    $post_type="jobman_job";
}
if ($query->is_search) {
    $query->set('post_type', $post_type);
};
return $query;
};

 add_filter('pre_get_posts','mySearchFilter');