Lennox Air Conditioner Error Code E429

E429 means the inverter drive in the outdoor unit did not build up sufficient DC link voltage within 30 seconds of startup. The required threshold is 180 VDC for 2 and 3-ton units, or 250 VDC for 4 and 5-ton units. This is reported internally as inverter fault code 23. The system shuts down to protect the inverter and compressor from operating under inadequate power conditions.

No. When E429 is active, the system has already shut down the compressor to protect itself. Attempting to force a restart repeatedly without diagnosing the root cause can stress the inverter components and potentially cause further damage. Leave the unit off and address the underlying power or component issue before attempting to restore operation.

Repair costs vary widely depending on the cause. If the fix is simply tightening connections or resetting a breaker, the service call fee of roughly $75 to $150 may be the only cost. If the inverter drive module needs replacement, parts and labor can range from $600 to $1,500 or more depending on unit tonnage and local labor rates. Getting a diagnostic visit to confirm the root cause before committing to parts is strongly recommended.

Some causes of E429, such as a tripped breaker or a visibly loose wire at the disconnect, can be addressed by a knowledgeable homeowner. However, diagnosing low line voltage, testing inverter components, and inspecting internal drive circuitry requires electrical testing equipment and knowledge of high-voltage DC circuits. Any work inside the inverter drive should be performed by a qualified technician, since DC bus capacitors can retain dangerous voltage even after power is disconnected.

A power reset may temporarily clear the fault display, but if the underlying cause is still present, the code will return within 30 seconds of the next startup attempt as the DC link again fails to reach threshold. Resetting without diagnosis is not a fix. The root cause, whether it is a power supply issue, loose connection, or failed inverter component, must be corrected for the fault to clear permanently.