Lennox Air Conditioner Error Code E431

E431 means the Power Factor Correction circuit inside the inverter detected an over-current condition of 100 amperes, which is logged as inverter code 27. The inverter shuts down automatically to protect its internal components from damage. The fault points to power supply problems such as a brownout or interruption, or to loose and corroded wiring at the inverter input. A technician should check main power quality and all electrical connections before attempting a restart.

No, the unit has already shut itself down as a safety measure and should not be forced to restart without identifying the underlying cause. Repeatedly resetting and running the system with a persistent over-current condition risks damaging the inverter board, compressor drive components, or associated wiring. Address the root cause before returning the unit to service.

Repair costs vary widely depending on the cause. If the issue is simply a loose wire or a tripped breaker, a service call diagnostic fee of roughly 75 to 150 dollars may be the only cost. If the utility power supply is the problem, an electrician may need to evaluate the service panel, adding to the expense. In cases where the inverter board has sustained damage and requires replacement, parts and labor costs can range from several hundred to over a thousand dollars depending on the specific inverter model and labor rates in your area.

Some basic checks are accessible to knowledgeable DIYers, such as inspecting the outdoor disconnect for loose or burned connections and checking the circuit breaker for signs of tripping. However, working inside the outdoor unit with live inverter components carries serious electrical hazard risk, and diagnosing power quality issues requires a multimeter or power quality analyzer. Most homeowners should have a licensed HVAC technician perform this diagnosis.

A power reset may temporarily clear the fault and allow the unit to restart, particularly if the cause was a one-time power interruption or momentary brownout. However, if the underlying issue is a loose connection or ongoing power quality problem, the fault will return. Clearing the code without correcting the root cause risks repeated shutdowns and potential hardware damage over time.