I hope you are not plugging into 220!
Hopefully you are plugging in the 30 amp shore power cord which is a 30TT 120 volt cord.
Since you are using a standard extension cord, I think you are not.
Batteries and converter working? Verify receptacle in the out side refer access for 120 volts. Use some type of appliance to verify(maybe an electric drill)
Good power to receptacle, check fuse on circuit board on refer.
No luck? post make and model of the refer. Label could be in refer or in outside access.