HVACopedia

Lennox · Heat pump

Green FAST flash / Red ON Discharge line temperature lockout

Medium severity Lennox EL16KP1Lennox ML14KP1

What the control is telling you

Discharge temp fault happened 5 times. With the compressor running, the control shuts off its contactor output (and defrost output if on). On these units, suspect the 10K resistor used in place of a discharge sensor.

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

Likely causes

  • Shorted 10K resistor on the discharge sensor connection
  • Wiring short at the discharge sensor terminals

Test and repair steps

  1. Check the 10K resistor on the discharge sensor terminals for a short; replace if bad.
  2. Check the resistor leads for contact with each other or the board.
  3. To clear a 5-strike lockout after the repair, place a jumper on the TEST pins (P1) or cycle 24 VAC power to the defrost control; then put the jumper back on the desired setting.

Settings for these units

Save it for the next call

Star this code in the HVACopedia app and keep the whole library on your phone for jobs with no signal.

Open the app

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.