Have you double checked to make sure it is wired and ported correctly?

If you know how to properly troubleshoot the system something like the following would be handy to verify that it is working correctly (though a pressure source and regulator would be needed to give you the right test pressures)

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=1871493352