For this diagnosis to work, the freezer must be frozen down or the evaporator must be encrusted with ice. Expose the evaporator coil as follows: Unplug the refrigerator. Remove the upper and lower panels from the back wall of the freezer compartment and the refrigerator section if you have a single door refrigerator. If you have a double-door unit, remove the back panel from the freezer section.
Plug the refrigerator back in. Locate the defrost timer inside the refrigerator compartment; you will see a slotted screw with a pointer. Insert a screwdriver into the slot and turn the timer screw so that the pointer is opposite the defrost mode.
At this point, the refrigerator will stop working. Locate the defrost heater mounted on or behind the bottom of the evaporator coil. Wait about five minutes. If the defrost heater is working, it will glow red and start melting the ice on the evaporator coil. If it fails to heat up, either the defrost timer is broken or the heater is bad and must be replaced.
Quote: Frost free fridges do freeze up but it s usually hidden in the gubbins at the back, so you don t know about it until the fridge gets warmer, then you turn it up more.
Clear away any ice you can get to, then leave the fridge switched off and open for at least twenty four hours to give the hidden ice a chance to melt.
Clean the seals and check they are intact. I have to do this to mine about once a year. Get a fridge thermometer because the display panel only tells you what temperature it s trying to achieve. If you put wet stuff in the fridge all that water has to go somewhere.