I also have a 2007 Diplomat SKQ. I just changed my rear unit out to a Penguin II 15,000 BTU from a 13,500. If your 13,500 BTU has been changed out to a 15,000 it has a new control board and the dip switches may be incorrect. I suggest get the model number and call Dometic Tech Service and ask them for help. When I talked to them on my change out they were really good. It is real easy to accidentally change a dip switch when installing everything. I am sure you went to the thermostat and choose zone 2 and then furnace. Maybe try that in case you accidentally chose the wrong mode. Good Luck