Hello I'm having a issue with a '91Van Dorn 400 rs 48f ht.... Clamp will not close auto,semi or Manuel. All switches are being made you can hear it wanting to close but no luck. Thought maybe the cn valve was bad so I switched it but still the same issue. Have a vdu control board and it doesn't have any errors or alarms displaying. Any help will be greatly appreciated. Thank you in advance.