First you have to conclude your hand held remote is not working or the receiver circuit inside the AC is not working. For handset try replacing the batteries. You can check the transmission with a regular camera phone by seeing the IR LED of the remote by the camera. If you see a blinking white light in the bulb, the handset works fine. If its the controlling circuit faulty, you need to call a service technician or try doing the fault finding yourself by tracing the circuits in.
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