AUTO is 120. If NO 120 available, the refer goes to LP. They have the LP selection so you can run on LP ONLY if you want to limit your 120 amperage consumption when you are on a 30 amp or lower shore cord power pole. The reason to have the AUTO configured this way is, IF you lose 120 power it will automatically run on LP, so you do not ruin food.
BTW, it only cools FASTER on LP for the first 15 minutes. Then both the 120 and LP will cool down at the same rate. Both LP and the 120 element have the same BTU ratings. Doug
