It looks to me that some PO has added the white wire to go to something else.
The larger black wire is most likely + 12 volts, the larger white wire is the - 12 volts. The smaller brown (?) and green wires most likely go to the refrigerator electrics. The white wire which goes to the splice is picking up +12 volts for something, and the other wire connected to the terminal with the phillips head screw holding it is being used as the -12 volts for whatever that wire set goes to.
I think if you trace the white covered wire set, you will find some 12 volt
load attached to them, so they are a using pair, not a supply pair.