Lennox Air Conditioner Error Code E427

E427 indicates the inverter has detected a DC peak current fault at or above 55 amperes, which is logged as inverter code 21. When this condition occurs, the inverter immediately shuts down both the compressor and outdoor condenser fan to protect the system. The fault is typically caused by high refrigerant pressure, a failing condenser fan, an overcharged system, or a seized compressor rotor.

The system automatically shuts down the compressor and fan when E427 is triggered, so it will not continue running in a dangerous state on its own. You should not attempt to repeatedly force restarts without diagnosing the cause, as doing so could worsen damage to the compressor or inverter module. Leave the unit off until the fault is properly diagnosed and resolved.

Repair cost varies widely depending on the root cause. Clearing a blocked condenser coil or replacing a condenser fan motor typically runs in the range of $150 to $450 including labor. Correcting a refrigerant overcharge may cost $100 to $300. Compressor replacement is the most expensive scenario, generally ranging from $1,200 to $2,500 or more depending on the unit size and refrigerant type. Inverter module replacement also falls in the higher cost range, typically $600 to $1,500.

Disconnecting power to the outdoor unit and performing a restart is the recommended first step, and the unit may temporarily resume operation if the fault condition was transient. However, if the underlying cause such as high head pressure, a bad condenser fan, or a seized compressor is still present, the E427 fault will return quickly after restart. A reset alone does not fix the root problem.

Start by disconnecting power to the outdoor unit and inspecting the condenser fan and coil for blockage or motor failure. A licensed technician should connect refrigerant gauges to check for overcharge or abnormally high head pressure. If those checks are normal, the compressor should be tested for a locked rotor condition. Any failed components, whether the fan motor, refrigerant charge, or compressor, must be corrected before the system can operate safely.