I had similar issues with heat/cooling control and come to find the hose on the vacuum pump was pinched right next to the pump. Corrected the pinched hose and now have lots of heat. This device opens and closes the air flaps in the heater plenum.
On mine it is located up front to the left of the generator. There is also a line that runs up to a vacuum bulb that slipped off due to its own weight. Tied it up to keep it in place.
2019 Unity LTV CB, pushed by a 2013 Honda CRV, BlueOx Baseplate, Aventa Bar & Patriot Brake