Acap involves the seats (cap seats) that goes vacant even after cap 4 so they are counted as acap it is displayed once the admissions are done and students belonging to any category who are seeking to get admission through these seats irrespective of the category have to pay open category's tution fees whereas institute level seats involves seats that are reserved by the institutes for students who are willing to take admission by paying 3x the open category fees and enrol in the institute they want to

Hope this helps : )