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Lennox · Air conditioner

E443 Unit code to inverter model mismatch

High severity

What the control is telling you

The variable capacity outdoor control has the wrong unit size code for its inverter. S30/S40 thermostat alert code 443 (shown as E443 on the unit control display).

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

Likely causes

  • Wrong unit size code
  • Replacement inverter does not match unit size

Test and repair steps

  1. Set the correct outdoor unit size code (configuration guide / installation instructions).
  2. If the inverter was replaced, verify its model matches the unit size.
  3. Remove the thermostat from the system while powering up and reprogramming.
  4. Clears after correct match following 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.43. 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.