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Lennox · Furnace

E155 Refrigerant leak sensor #2 communication lost

High severity Lennox ML180UHE

What the control is telling you

The control has lost communication with refrigerant detection sensor #2. The blower latches on for at least 5 minutes after communication returns.

Applies to: ML180UHEK (R-454B era) single-stage 80% furnaces with integrated control 107792-XX (ML180UH045/070/090/110/135, incl. low-NOx X models)

Likely causes

  • Damaged or unplugged sensor #2 harness or connector
  • Sensor #2 damaged or plug obstructed
  • LGWP2 enabled with no second sensor fitted

Test and repair steps

  1. Confirm whether a second sensor is required/installed; if not, set LGWP2 to Disable.
  2. Check the sensor #2 cable at the LGWP2 plug for proper seating, damage or moisture.
  3. Inspect the harness route (right side grommet) for cuts or pinches.
  4. Press the LGWP test button to retest the fault after repair.

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Source: Lennox ML180UHEK Unit Information 100161/100166, Table 6 Integrated Diagnostic Codes, p.14; Table 17, p.33. Summarized in our own words; check the original manual for your model.

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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.