I noticed the back of the freezer compartment where the evaporator coil lives started forming a big frost patch on the back panel. I knew that wasn't normal, so I removed the back panel to investigate and found an ice ball on top of the evaporator coil. The refrigerator was still performing pretty good at this point with the ice ball. I used a hair dryer to melt the ice ball off the evaporator and put the panel back on. Figured it would help the performance, but now the refrigerator is not cooling down enough to keep food totally frozen in the freezer compartment even with the thermostat set colder than normal. Nothing else was touched or changed ... any ideas?