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Lennox · Air conditioner

E407 Compressor open run circuit

High severity

What the control is telling you

Not enough current through the RUN current transformer. S30/S40 thermostat alert code 407 (shown as E407 on the unit control display).

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

Likely causes

  • Open run winding or wiring

Test and repair steps

  1. Check run circuit wiring through the current transformer and compressor run winding.
  2. Clears after current is sensed in RUN sensor, 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.

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.