You do not state year model. BUT, Dometic refers for the last 15 years have a overheat snap disc on the burner flue cover. The refer requires 12 volts to do anything as the controls are 12 volt. The 120 part just supplies 120 to the AC Heat Element. The AC element is controlled by the 12 volts. There will be 2 small wires going to a + and - plastic lug on the refer. The must be positive there. Then the 12 volt power goes to that overheat disc on the burner flue(2 red wires). IF that snap disc is bad, then you will not get power to the refer. You can jump those 2 red wires to see if the snap disc is bad as the refer will then power up the inside control buttons. If that is the case, then get a new Overheat disc from a RV service center. That disc is a SAFETY required part. Doug