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Lennox · Air conditioner

E412 Open high pressure switch

Low severity

What the control is telling you

High side pressure is above the upper limit; the system shuts down (dealer information). S30/S40 thermostat alert code 412 (shown as E412 on the unit control display).

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

Likely causes

  • Overcharge
  • Condenser fan failure or dirty outdoor coil
  • Expansion valve problem
  • Indoor blower failure (heat pump heating)
  • Stuck reversing valve or clogged filter drier

Test and repair steps

  1. Confirm correct refrigerant charge.
  2. Check the condenser fan motor, expansion valve, indoor blower, reversing valve and filter drier.
  3. Clean the outdoor unit.
  4. Clears when the switch closes or after 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.30. 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.