Icing (ice block on the evaporator)
Also known as: iced evaporator, ice build-up, evaporator ice-up
Short definitionFrost that does not fully melt during defrost refreezes and covers the evaporator in a hard mass of ice. Air cannot pass and the room warms up; a defrost or drainage problem is usually behind it.
Frost and ice are different things. Frost is white and loose, and a healthy defrost melts it every time. If the defrost is cut short, the meltwater refreezes before it reaches the drain pan and a clear block forms that thickens with every cycle. The block usually starts at the bottom rows and the rear face, fills the pan and finally reaches the fan.
The decisions that prevent icing are made at the design stage: defrost heaters with enough power, a termination sensor fitted in the right place, a sloped drain pan, and in a freezer room a heated drain line with a trap. If the door stays open or the gaskets leak, no defrost can cope with that much moisture. Existing ice is melted with a long defrost or warm water; chiselling it off punctures the tubes.