Refrigerator runs constantly and still not cold enough; heavy frost on freezer back wall.

Safety first: Unplug the refrigerator before accessing the evaporator and heater.

Immediate relief:

• Perform a full manual defrost by unplugging the unit, opening doors, and allowing all ice to melt (use towels to catch water). This will restore cooling temporarily.

Diagnosis:

• Remove the freezer rear panel and inspect the evaporator for heavy ice.
• Test the defrost heater and thermostat for continuity; replace any open components.

Corrective action: Replace the failed defrost heater or thermostat. If both are good, the main control board may not be initiating defrost and should be replaced.