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Lennox · Heat pump

Green ON / Red ON Demand defrost control failure

High severity Lennox EL16KP1Lennox ML14KP1

What the control is telling you

Both LEDs on steady: the control detected an internal component failure.

Applies to: Lennox EL16KP1 (Elite) and ML14KP1 (Merit) R-454B heat pumps, sizes -018 to -060, demand defrost control A108 (CMC1)

Likely causes

  • Internal failure of the demand defrost control

Test and repair steps

  1. Turn the 24 VAC power to the control off and back on.
  2. If both LEDs come back on steady, replace the demand defrost control.
  3. After replacing, set the termination (P1), nominal defrost time (P3) and DELAY (P5) jumpers the same as the old board.

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Source: Lennox EL16KP1 Unit Information 100195 / ML14KP1 Unit Information 100108, Table 4 Demand Defrost Control (A108) Diagnostic LEDs, p.32. Summarized in our own words; check the original manual for your model.

Homeowner looking at this code? See what it means for you and when to call a technician.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.