How can a refrigerator's efficiency be greater than 1?

Because it is not directly transforming work into temperature differential. Rather it is using work to move heat from one place to another. In some sense, the efficiency calculations we use to rate the efficiency of thermal machines don't apply to refrigerators. read more

If the efficiency were one, the amount of heat removed from the inside would be exactly the same amount of heat dissipated from the compresor. And if the efficiency were larger than one you would be removing more heat from the inside than the amount of heat dissipated by the compressor. read more