Lennox · Air conditioner

E417 Discharge sensor faulty

Medium severity

What the control is telling you

Discharge line temperature sensor open, shorted or out of range (checked after 90 seconds). Escalates after 10 minutes. S30/S40 thermostat alert code 417 (shown as E417 on the unit control display).

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

Likely causes

Failed sensor
Sensor leads in the wrong pins of the harness connector

Test and repair steps

Check sensor resistance against the temperature/resistance chart in the unit instructions; replace if out of range.
Verify harness pin positions against the unit's terminal table; order a replacement cable assembly if the pins are wrong.
Critical condition power down, replace sensor or cable, power up to clear.

Settings for these units

Outdoor unit clearances · Lennox EL16KC1

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Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.31. Summarized in our own words; check the original manual for your model.

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