EC 21 is a defrost overheat: the freezer evaporator went past the temperature a defrost is meant to stop at, so the control ended the cycle and recorded why.
- What the control is watching
- How far the freezer evaporator warms while a defrost is running, and whether the cycle finishes where the design says it should.
- What makes it register
- Heat arriving faster than the cycle allows for, or heat still arriving after the cycle ought to have shut itself down.
- Can you keep using it
- For a short while. The food compartment takes the surplus, so frozen goods soften at the edges and the compressor then works to pull it all back out.
Direction is everything with this one. Its neighbours in the table report a defrost that never got warm; this reports a defrost that got too warm, and the two lead to opposite places. Too little heat usually means a dead element. Too much usually means the heat itself is fine and something has shifted.
What shifts is either a part or a temperature. The freezer evaporator thermistor and the defrost heater each have a position the design intends, and a cover taken off and put back is enough to change it. Failing that, the terminator that ends the cycle has drifted out of its rated range.
Meanwhile the compartment is what suffers. Heat that ought to leave with the meltwater stays in the box instead, and everything on the top shelf knows it.
What we usually find
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The code turning up on a cabinet where the evaporator cover has been off for other work recently
The freezer evaporator thermistor or the heater refitted a little way from where it belongs. Heat and sensor have to sit in the positions the design gives them.
Defrost heater, thermostat or sensor $280–$640
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Overheating repeated cycle after cycle, on a coil that does clear itself properly each time
A defrost terminator no longer opening where it is rated to. Cut-in is 30°F and cut-out 55°F across these models, with the 601F-3 the exception at 70°F.
Defrost heater, thermostat or sensor $280–$640
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The reading first showing up in the weeks after a control board was fitted to the cabinet
The blue heater wire on the wrong terminal, or shorted across to a neighbouring circuit, so the element is being energised outside the cycle meant to limit it.
Quoted after the diagnosis
Which of these it is gets settled at the visit, before a part is ordered — Sub-Zero Repair Pro Los Angeles, (310) 844-1973.
- Written by
- Yuki Tanabe
- Role
- Refrigeration technician — controls and sensors
- In the trade
- 18 years in the trade
