Credit set up is not active for the sales order type (OVAK) or the delivery type (OVAD).
the above two settings are credit checks at what level( example order level or delivery etc) you what to block the customer if the customer payer exceeds the credit limit.
Where as if the credit active field is active in VOV7 in corresponding item category, system update the respective document values in to credit management (FD32/33) in your example open order value.
Even though OVAK, OVAD settings are not done still system update the document values in to FD33 subject to credit active field is active in t code VOV7 .
Please check in your item category whether credit active field active.
thanks,
Srinu.