Lennox Air Conditioner Error Code E435

E435 indicates an inverter internal error, specifically inverter code 60, on a Lennox inverter-driven air conditioning system. When this fault occurs, the outdoor control board automatically cycles power to the inverter in an attempt to clear the error. If the fault is not resolved after three power cycle attempts, the outdoor unit locks out completely. The EEPROM chip inside the inverter is the first component to check, as a loose or failed EEPROM is a leading cause of this error.

The system is designed to protect itself by locking out the outdoor unit after three failed restart attempts, so it will not continue running in a potentially damaging condition. You should not attempt to repeatedly override or reset the lockout without identifying and correcting the underlying fault. Continuing to force the system to run with an unresolved inverter fault can cause further damage to the inverter module or compressor.

Repair costs vary depending on the root cause. If the EEPROM only needs to be reseated, costs would primarily cover a service call, typically in the range of $80 to $200 depending on the region and provider. If the EEPROM chip itself requires replacement, parts and labor could range from $150 to $400. A full inverter module replacement is considerably more expensive, often falling in the range of $600 to $1,500 or more depending on the specific model and labor rates.

The initial diagnostic step, confirming the EEPROM chip is properly seated, requires opening the outdoor unit and handling electronics, which is best left to a qualified HVAC technician. If the EEPROM simply needs reseating, the repair is straightforward for a technician but carries risk of further damage if performed without the proper knowledge and tools. If the inverter module itself has failed internally, replacement of that component is required and is not a DIY repair.

The outdoor control board already performs up to three automatic power cycles to the inverter when E435 is detected. If those three attempts do not clear the fault, the unit locks out and a simple power reset is unlikely to resolve the underlying problem. A technician must inspect the EEPROM seating and evaluate the inverter module before the system can safely return to normal operation.