
Originally Posted by
oj88
Some "no-frost" refrigerators don't have a manual defrost button. It usually runs as a timed event. When the program comes up (usually through a mechanical timer), the compressor and fans turn off then a heater near the evaporators fires up to melt the ice. Typically, the ice don't get too thick and the heater duration is enough to melt everything until the cycle to turn on the compressor and fans comes up.
However, if the condensate drain is clogged, that will cause condensate water to back up and turn to an ice block. This will usually block the intake vents so there'll be little to no airflow. The mass of the ice can be too much even for the heater to melt in time. And even if it does, with the drain clogged up, there's nowhere for the water to go after it melts. As soon as the defrost cycle is done, it's turned back into a block of ice.
This recently happened to our LG no-frost ref of 15 years. They needed to de-clog the drain and do some general cleaning. There were a lot of gunk on the evaporator condensate catch pan.
Our older no-frost ref had a similar issue but it was a problem with the heater thermostat. It stopped working so even when the defrost cycle was on, the heater didn't work. This caused excessive icing and neither the freezer nor the ref compartment were getting any cold air.