If your Dometic AC has a heat pump, you can tell by the presence of a reversing valve. This valve is located on the back of the unit and has two positions: one for cooling and one for heating. When the valve is in the cooling position, Freon flows through the evaporator coil to cool the air inside the RV. When the valve is in the heating position, Freon flows through the condenser coil to heat the air inside the RV.