What you have here, I think, is an automatic defrosting fridge/freezer. (You didn't say)
If that's the case, the water, when it defrosts, runs down the inside rear of the fridge/freezer, and goes through a small hole near the bottom...This, in turn USUALLY drips onto the condenser, (The big round black thing at the back of the machine) where it evaporates..Depending on what make you have, there may be a blocked tube, preventing this from hapening.
Pull the fridge away from the wall, so you can get behind...Push something long and flexible through the hole and check where it comes out around the back.
You can, when sure it's clear, pour a little water down, and see if it drips onto the condenser.
This has taken me ages to type, I hope it works for you.
CHUMLEY, January 2010