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Lennox · Air conditioner

E408 Compressor contactor welded

High severity

What the control is telling you

The compressor runs continuously. S30/S40 thermostat alert code 408 (shown as E408 on the unit control display).

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

Likely causes

  • Welded contactor contacts

Test and repair steps

  1. Warning: Disconnect power before checking the contactor.
  2. Replace the contactor if contacts are welded.
  3. Clears after one normal run cycle or power reset.

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Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.29. 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.