RV Repair: Dometic RM 190, dc power supply, 12 volt lights

Question
I recently purchased a 1982 Palomino Pinto that came with a Dometic RM190 Fridge.  The seller was not very knowlegeable regarding the camper, so he was no help.  When I plug the camper into my extension cord the inverter begins to hum, and I can turn the lights on.  My question is how to turn on the frige.  I opened the vented door on the back of it and see the gas connections but no switch to say turn from a/c to gas.  Is there a hidden switch?  I have a friend who has a scamper and on the back of thier fridge there is a three way switch A/c, Gas, D/C.  Also one other question is it alright if the inverter runs all the time even if the lights are off?  Or should it run only when the 12 volt lights are on?  Thank you in advance.  Mike

Answer
Hi Mike:
As I recall the RM190 is pretty much a manual frig. There should be some controls on the lower left as you open the refrigerator door inside the camper. There is a selector switch you have to turn to gas then ignite by pushing the igniter while you hold the bypass button. Once it lights the burner heats up a sensor that will keep the gas flowing after a few minutes. During this time you have to keep the bypass button pushed in. Thats the system unless somebody has upgraded the frig which is possible in a 1982.
I doubt that what you hear is an inverter, it is probably a converter. An inverter makes AC voltage out of DC voltage while a converter makes DC voltage out of AC. The trailer probably uses a converter/DC power supply to run 12 DC stuff and charge the battery. The battery is probably stone dead which is why the lights do not come on until you plug it into AC. Once you charge the battery fully, or get a new one if the old one will not hold a charge, you could turn the converter off and the lights will work for a few hours. It does not hurt the converter to run all the time. If you really do have an inverter the story is different so you need to check and let me know.
Bill