Lennox SLP98UHV Error Code E 407: LSOM - Compressor Open Run Circuit
What Does Code E 407 Mean?
Error code E407 on the Lennox SLP98UHV indicates that the Lennox Smart Outdoor Monitor (LSOM) has detected an open run circuit in the compressor. The run winding is the main motor winding that keeps the compressor operating after it has started. An open run circuit means the compressor cannot maintain operation.
Like E406, this condition can be caused by a compressor that has overheated and tripped its internal thermal protection. The difference is that the run winding circuit is affected rather than the start winding. When both the start and run circuits show open conditions, it often indicates a thermal protector trip rather than individual winding failures.
A technician should let the compressor cool down completely, then check for the root cause of the overheating — insufficient airflow across the condenser, low refrigerant, a failed fan motor, or other system issues. Once the compressor is cool, the motor windings should be tested. If the run winding reads open with a cool compressor, the compressor must be replaced.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Compressor run winding failure or internal thermal protection tripped | Most common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- The AC stops cooling and the furnace displays E407
- The compressor was running and then suddenly stopped
- E407 appears along with E406, suggesting thermal protector trip
✓ Verified against manufacturer service manual — March 2026