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Lennox · Air conditioner

E431 Inverter PFC fault (inverter code 27)

High severity

What the control is telling you

PFC circuit detected over-current of 100 A peak; unit stops. 10 times in 60 minutes = lockout. Inverter LED flash code 27 (red 2 flashes, green 7 flashes). S30/S40 thermostat alert code 431 (shown as E431 on the unit control display).

Applies to: Lennox communicating air conditioners incl. variable-capacity inverter units in S30/S40 smart thermostat systems

Likely causes

  • High load
  • PFC circuit fault

Test and repair steps

  1. Refer to the unit service manual.
  2. Clear by disconnecting power to the outdoor unit and restarting.
  3. Check inverter LEDs flash code 27 = red 2 flashes, green 7 flashes. Normal inverter LEDs with no fault: red ON, green OFF.

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Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.36. 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.