An autoformer is a device used to boost low campground voltage, allowing AC (120V) equipment to operate when they couldn’t operate at the lower voltage, or would burn out. In general air conditioners should not be run when the voltage is below 108V.
Low campground voltage can be due to older wiring that is too small for the high current draw of newer RVs. The voltage at the site power pedestal falls due to the voltage dropped along the campground wiring. If the voltage coming into an RV drops too low, motors such as the ones in air conditioners will draw additional current and could overheat.
An alternative solution would be to avoid running the air conditioners when the voltage drops below “safe” levels. However, this could be uncomfortable when it’s hot. The pedestal voltage could rise again due to varying loads on the campground electrical circuits. Using an autoformer automatically responds to increases and drops in pedestal voltage.