A/C Wiring Question

I posted this on the Facebook group, but thought I'd also post here.....

I have a question for any of you who have upgraded your A/C units.

I have a 2021 year model 2552 with the 50A, 2 A/C upgrade.

I'm getting ready to swap my units out tomorrow to Houghton units.  I already started removing the interior stuff so I can get the wiring organized and deal with the furnace.  I ran into something that I'm a bit confused about.
The 120v wires are obvious.  The low voltage wiring is the issue.  The rear unit is easy.  There is a 120v Romeo wire, a 12v+ and a 12v-, and then a communication wire that is wired to the rear thermostat above the passenger side bed.  Easy enough. 

The front unit has the 120v romex wire, a 12v+ and 12v- into the unit, and what looks like the 2 thermostat wires to control the furnace.  Additionally, there are two communication wires.  One of them goes to the front CCC2 thermostat.
Where does the other one go to?  My first thought was that the communication wire would go back to the second A/C unit because the CCC2 thermostat in the front could theoretically run both units set up as a multi-zone system.  However, the factory didn't seem to wire it that way.  If they had, there would be no need for the rear thermostat and also, that second communication cable would have to exit into the rear A/C.....which it doesn't.  It just goes into the ceiling and disappears. 
Any ideas what that second comm cable could be used for?  Thanks.

A pure GUESS

IF you are parked at a 30amp site, only the rear thermostat would do anything.  The front "communicationp" cable could be to allow you to use the front a/c (when plugged into a 50a site) to control the furnace by itself with the rear thermostat shut off.  I do know with the standard wiring with the Dometic Penguin, the A/C unit actually is connected to the furnace and turns the furnace on/off based on the rear thermostat.  That's the way my 2015 model 2551 is wired.

I have no idea of the Houghton can control the furnace.  Again, Dave Ponser should have the answers you need.

The best, and correct answer would be to call Phoenix and to speak with Dave Ponser.

A pure GUESS

IF you are parked at a 30amp site, only the rear thermostat would do anything.  The front "communicationp" cable could be to allow you to use the front a/c (when plugged into a 50a site) to control the furnace by itself with the rear thermostat shut off.  I do know with the standard wiring with the Dometic Penguin, the A/C unit actually is connected to the furnace and turns the furnace on/off based on the rear thermostat.  That's the way my 2015 model 2551 is wired.

I have no idea of the Houghton can control the furnace.  Again, Dave Ponser should have the answers you need.

The best, and correct answer would be to call Phoenix and to speak with Dave Ponser.

On my unit, the front thermostat runs the furnace.  So 30a or 50a, it all runs the same.  Newer 2021 model with the digital thermostats.