HVACopedia

Lennox · Heat pump

Green & Red alternating SLOW flash 5-minute anti-short-cycle delay

Low severity Lennox EL16KP1Lennox ML14KP1

What the control is telling you

Status, not a fault: the control is holding the compressor off for 5 minutes after power-up, after a safety trip, or after a thermostat call ends. (Both LEDs flashing slowly together = normal operation/standby.)

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

Likely causes

  • Power was just applied
  • A pressure switch or other safety just tripped
  • Thermostat call just ended

Test and repair steps

  1. Wait out the 5-minute delay; the unit should start on its own if there is a call.
  2. To skip the delay during service, jumper the TEST pins (P1).
  3. If the unit keeps returning to this delay, look for a safety that keeps tripping (watch for low or high pressure fault codes).
  4. Put the jumper back on the defrost termination pins when finished.

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.