Andy, I recommend you look at your electrical panel and see if you find an unused breaker or an empty slot for a breaker. All 2022's were advertised as being factory built pre-wired for a 3rd AC. My 2022 came with the 3rd AC installed by the factory in place of the MaxAir fan and has it's own breaker in the panel. (There's also a loop for that circuit in the basement to connect it to a larger inverter as part of the SolarFlex 400i package, but that won't apply in your case.) I've seen posts in other places where people remove the vent and find the wire terminated there along with the thermostat control wire.
Other things to note - you probably won't be able to connect the 3rd AC to the duct/vents in the ceiling. Mine is a "dump" AC that pumps cold air out one side and sucks in the return on the other.
The other challenge you may have is getting the new unit on the roof and in place. I've had to have an AC replaced under warranty and my dealer used a forklift and two burly guys to move the units around.
Good luck!!
