220v / 12v shoreline fridge

Hi, I have acquired a Shoreline RR47 fridge which is a 12/24v and 220v but have no operating instructions. I can wire up the 12v ok and am aware of the voltage drop issues. The fridge is currently running on 220v shore power. I cannot find instructions on the Shoreline Website for 220v option.
 I cannot find a switch to change from 220v to 12/24v does it change over automatically or do I have to pull out the 13amp plug before switching on the 12v supply and vice versa
Thanks