Lennox Air Conditioner Error Code E411

E411 means the low pressure switch in the refrigerant circuit has opened five times within one hour, causing the outdoor unit to lock out as a protective measure. The low pressure switch trips when suction pressure falls below a safe operating threshold. Common causes include low refrigerant, a clogged TXV, a dirty air filter, or a restricted blower. The system will not restart until the root cause is resolved and a power reset is performed.

No. The E411 lockout is a protective function that prevents the compressor from running in a low-pressure condition, which can cause serious compressor damage. Attempting to bypass the lockout or repeatedly resetting power without addressing the underlying cause risks permanent compressor failure. Leave the system off until the fault is properly diagnosed and repaired.

Repair costs vary significantly depending on the cause. A simple air filter replacement costs very little, while locating and repairing a refrigerant leak and recharging the system can range from a few hundred dollars to over a thousand dollars depending on refrigerant type and leak location. A TXV replacement or filter drier replacement typically falls in the range of a few hundred to several hundred dollars including labor. A technician diagnostic visit is usually required to determine the exact cause and provide an accurate estimate.

Some causes, such as a dirty air filter or an obvious blockage at the indoor unit, can be addressed by a homeowner. However, diagnosing and correcting refrigerant charge issues, a failed TXV, or a clogged filter drier requires specialized tools and EPA certification to handle refrigerants. If replacing the filter and ensuring clear airflow does not resolve the fault after a power reset, a licensed HVAC technician should be called.

A power reset will clear the E411 lockout and allow the system to restart, but it will not fix the underlying problem. If the root cause, such as low refrigerant or a clogged TXV, is still present, the low pressure switch will continue to trip and the E411 lockout will return quickly. A power reset is only useful after the actual cause has been diagnosed and corrected.