Let me state what others have already suggested a different way.
If you have all the parts, set it up so that it works as intended.
Now you have two easy spots to spy on what it is doing and gain from all that is already done.
You could spy on connections between outside unit and outside transmitter.
You could spy on connections between inside unit and inside transmitter.
Why spy, because the unit will keep functioning if your spy connections do not do something like draw to much current to prevent normal operation.
You now have what is shown on TV to see if your guess is correct with the data format on spy connections is correct.