In my original thread linked above member GCLARK recieved a bad contol box from Camping World. If you have 120v power and 12v power coming in to the box and checked the rest of the connections I am not sure what else to say. I assume you read through my install thread and it was very straight forward. All I can think is the box is bad... unless were you having any trouble before?
Does the furnace work?
How cold is it? Might be too low to run the A/C?
I did read an issue that too high of temp (~105F?) will cause the thermostat to not engage... don't know if there is a low temp spec.
Any thermostat error code?