Hello,
you need to mark the condition as negative.
check if you have not marked this condition as STATIC in the pricing procedure.
you can use the new condition with condition type A and calc type A ,
create the account key and asign it in the pricing procedure then do the rest config as you described.
Refer following link which explain steps in detail.
Posting planned delivery cost to Non-inventory account - ERP Operations - SCN Wiki
thanks
kUnal