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Lennox · Heat pump

Green OFF / Red OFF No power to the demand defrost control

Medium severity Lennox EL16KP1Lennox ML14KP1

What the control is telling you

Both LEDs on the defrost control (DS2 green, DS1 red) are dark: the board has no 24 VAC between R and C, or the board has failed.

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

Likely causes

  • No 24 VAC at defrost control terminals R and C
  • Indoor transformer, fuse or low-voltage wiring problem
  • Failed demand defrost control

Test and repair steps

  1. Measure 24 VAC between R and C on the defrost control.
  2. If there is no voltage, check the indoor unit transformer (24 VAC, 40 VA minimum), its fuse and the thermostat wire between indoor and outdoor unit.
  3. Check the low-voltage connections at the outdoor terminal strip for loose or broken wires.
  4. If 24 VAC is present at R and C and the LEDs still do not light, replace the demand defrost control.

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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.

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