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Lennox · Air conditioner

E436 Inverter high heat-sink temperature (inverter code 62)

High severity

What the control is telling you

Heat sink exceeded the inverter limit; inverter first slows (code 13), then stops the unit. Five times in an hour = lockout. Inverter LED flash code 62 (red 6 flashes, green 2 flashes). S30/S40 thermostat alert code 436 (shown as E436 on the unit control display).

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

Likely causes

  • Loose screws between heat sink and inverter board
  • Blocked heat sink airflow

Test and repair steps

  1. Warning: Wait five minutes for capacitors to discharge before touching the inverter.
  2. Tighten the screws holding the heat sink to the inverter board.
  3. Check the heat sink for debris and airflow obstructions.
  4. Service urgent disconnect power to the outdoor unit and restart to clear.
  5. Check inverter LEDs flash code 62 = red 6 flashes, green 2 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.40. 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.