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Lennox · Air conditioner

E181 Outdoor suction pressure transducer fault

Medium severity

What the control is telling you

Suction pressure transducer signal above 4.75 V or below 0.25 V for 24 h (+/- 3 h); unit runs on staged operation. S30/S40 thermostat alert code 181 (shown as E181 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 transducer, harness or connection

Test and repair steps

  1. Check the transducer harness and connector at the outdoor control.
  2. Check the transducer output voltage (0.25-4.75 V valid range).
  3. Replace the transducer if out of range.
  4. Resets after 3 consecutive in-range readings.

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Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.18. 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.