Lennox SLP98UHV Error Code E 404: LSOM - Compressor Rotor Locked
What Does Code E 404 Mean?
Error code E404 on the Lennox SLP98UHV indicates that the Lennox Smart Outdoor Monitor (LSOM) has detected a locked rotor condition in the compressor. The compressor was short-cycling (running less than 4 minutes per cycle) and the motor is now unable to spin, drawing locked-rotor amps.
A locked rotor means the compressor motor is receiving power but the motor shaft cannot turn. This causes the motor to draw extremely high current (often 5 to 10 times its normal running amps), which will quickly trip the compressor's internal thermal protector or external circuit protection.
The compressor may be mechanically seized due to internal bearing failure, liquid slugging damage, or contaminants in the refrigerant system. In some cases, a hard-start kit can temporarily overcome a sluggish compressor, but a truly locked rotor typically means the compressor has reached the end of its life and needs replacement. A technician will evaluate the compressor's condition and determine the best course of action.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Compressor motor mechanically seized or locked up | Most common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- The outdoor unit buzzes or hums but the compressor does not run
- The circuit breaker for the outdoor unit keeps tripping
- The AC has stopped cooling entirely and E404 is displayed
✓ Verified against manufacturer service manual — March 2026