That second knob is the thermostat on the air conditioner, it cycle according to the knob setting. I am not sure which model AC unit you have, but I just dropped the air distribution box on mine and it looks there is room for a standard module board and the roof top unit just plugs into that board. That means you have to pick up a ground and four more leads all very light gauge. Your AC power is already there.
On my Northstar I tried to figure out routing and it is possible, but will really be a challenge, all hidden. If you run on the ceiling surface mount it should be pretty simple although not pretty. For the Norcolds (Airxcel) the standard board for sale on Amazon should work, it comes with a freeze control that inserts into the evaporator coil.
I am saying this after a quick look, but other than the wiring, it looks like it should be pretty standard.
Steve and Andra
2012 F350 6.2 gasser SRW LB
Fab Fours front and rear in case we run into a rhino
2019 Northstar Laredo SC