Lennox · Heat pump

Green FAST flash / Red OFF Discharge sensor lockout

Medium severity Lennox EL16KP1Lennox ML14KP1

What the control is telling you

The discharge sensor (10K resistor) fault repeated 5 times and the control locked out.

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

Likely causes

Open 10K resistor on the discharge sensor connection
Resistor disconnected or loose

Test and repair steps

Check the 10K resistor on the discharge sensor connection; replace if open, reseat if loose.
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

Outdoor unit clearances · Lennox EL16KP1
Outdoor unit clearances · Lennox ML14KP1

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.