Clean your refrigerator's condenser coils every 6 to 12 months
Added
Unplug the fridge, find the coils on the back or behind the bottom grille, then brush and vacuum off the dust. Dusty coils make it harder for the fridge to shed heat, so cleaning them helps it cool food quickly and run efficiently.
The result
Result: DOE Building America Solution Center (PNNL): cleaning the coils every 6 to 12 months improves the refrigerator's efficiency, performance and lifespan; plan to finish within about two hours so food doesn't spoil.
Note: Unplug the refrigerator before cleaning and avoid bending the coils or tubing.
Source
DOE Building America Solution Center (PNNL): Clean Refrigerator Condenser Coils (opens the original source in a new tab). Check it for the latest numbers before you act.