Why dont you somehow just attach the IR led emitter near or on the the A/C's IR receiver. Maybe it can be done under the A/Cs external housing so it doesnt show from the outside. Then you just route a couple of wires to your board that drive the LED. Use twisted pair for this purpose.
That way you wont interfere with the unit's electronics and you will maintain isolation.
By the way
- got status from AC LED (ON-OFF, coole-heat) - DONE
How did your get the cool-heat status?