Lennox Air Conditioner Error Code E443

E443 indicates that the inverter drive has an incorrect unit size code programmed into it. The inverter uses this code to set operating limits and control parameters, so a mismatch between the programmed code and the actual unit capacity prevents the system from running. This error commonly appears after an inverter replacement or during initial commissioning if the wrong size was selected.

A simple power reset will not clear E443 because the fault is caused by a configuration mismatch, not a temporary sensor or communication glitch. The incorrect size code remains stored in the inverter after power is restored, and the error will return immediately. The size code must be corrected through proper programming before the fault will clear.

If the issue is only a programming error, repair costs are typically limited to a service call fee, which generally ranges from $75 to $200 depending on location and provider. If the inverter was replaced with an incompatible model, additional costs for the correct replacement inverter can range from $300 to $800 or more for parts alone, plus labor. A technician will need to assess whether the existing inverter is compatible or requires replacement.

Reprogramming the unit size code requires accessing inverter configuration settings, which is a task typically performed by trained HVAC technicians. The process also involves disconnecting the thermostat before applying power to the unit and entering the correct code. Attempting this without familiarity with inverter programming procedures and electrical safety practices is not recommended for most homeowners.

The system will typically not operate normally while E443 is active, as the inverter blocks operation when a size code mismatch is detected. This is a protective measure to prevent the compressor and related components from running under incorrect control parameters. You should not attempt to bypass this fault and should have the configuration corrected before resuming normal operation.