Method of control for a refrigerated merchandiser

A method of controlling a refrigerated merchandiser, comprising:

• providing a case defining a product display area and an air passage having an inlet that receives air from the product display area and an outlet that delivers air to the product display area;
• positioning an evaporator in the air passage to refrigerate the air;
• positioning a fan in the air passage to move the air through the passage;
• logging a first temperature value during frost-free operation of the evaporator, the first temperature value associated with at least one of the air entering the inlet of the air passage, the air exiting the outlet of the air passage, and saturated evaporator temperature;
• logging a second temperature value during frosted operation of the evaporator, the second temperature value associated with at least one of the air entering the inlet of the air passage, the air exiting the outlet of the air passage, and saturated evaporator temperature;
• calculating a difference of the first and second temperature values;
• and
• defrosting the evaporator when the difference exceeds a pre-determined value.