Zen-Cart - v1.3.8a

I have several flat rate shipping modules derived from flat.php. One of those must be excluded at checkout if the order total is $50 or more.

I added the following code at line ~60.

if ($_SESSION['cart']->show_total() > 49.99) {
$this->enabled = false;
}
It works fine at checkout but any reference to the $_SESSION when the module is called from Admin/Shipping Modules causes the module to fail. If $_SESSION is referenced in anyway from Admin, even isset(), defined(), or function_exists(), the module failsand all remaining shipping items and the editing box to the right on that page fail to display.

Given that my objective is to disable this shipping method if order amount is $50 or greater:

1) Is there a way to reference the order total that will work from admin and the catalog?

2) Is there a way to ignore the code block from just admin?