[Krssst]

If the message sent over IR always contains the full state, then it's only a matter of checking that the message was received.

If you are in the room, you'll know soon enough, otherwise I guess it could be possible to rely on the audio feedback (a light beep) that the AC probably emits when it successfully receives a command. (and add a temperature sensor to check that it's working properly)

[skykooler]

Not all state is necessarily transmitted over IR. For example, my unit has a button on the remote to turn the LED on or off; over the air this is just a toggle, only the AC knows which state the LED is in. (That said, that particular issue is easy enough to handle since changing any other parameter turns the LED back on, putting it back in a known state; there's no way to keep it off.)