Before repairing the AC remote control, first make sure of the followings.
1. Check the battery and make sure it is not fully discharged. Try to check it by using new ones.
2. If still AC remote is not working, try to rub end points of battery and its corresponding joint in remote. It may possible that due to rusting, electrical charge may not pass through it.
3. If all of the above steps do not solve your problem, you go to AC repair worker or shop and ask them to do needful.
4. If repairing is not solved, you should buy new one.