IR Remote Decoding for AC

I have a samsung AC and I can decode the hexadecimal signal, but when I send the AC it does not turn on

power on/off button

Unknown encoding: 15A5DB1B (32 bits)
Raw (32): 100 -500 500 -500 500 -500 500 -500 450 -550 450 -500 500 -450 550 -450 500 -500 500 -450 550 -500 500 -450 500 -500 500 -500 500 -2950 2950

On/off for an airconditioner usually sends a lot more information than just "on". It would normally send all of the data on the current settings, such as temperature and fan speed.

Try changing the settings and see how that changes the IR signal.

If you don't change settings, does the IR signal change? The remote might be sending the current time or some other kind of synchronisation, which you need to replicate with the Arduino.

The raw codes look strange to me, and don't correspond to any known protocol (hence "unknown encoding"). Please check your code and wiring.