Lennox SLP98UHV Error Code E 405: LSOM - Compressor Open Circuit
What Does Code E 405 Mean?
Error code E405 on the Lennox SLP98UHV indicates that the Lennox Smart Outdoor Monitor (LSOM) has detected an open circuit condition in the compressor. This means electrical current cannot flow through the compressor motor because the circuit is broken somewhere.
An open compressor circuit can be caused by several things: a failed run or start capacitor, a broken wire or loose connector in the compressor wiring, a failed compressor contactor, or most seriously, a burned-out compressor motor winding. When a motor winding opens (breaks internally), the compressor cannot be repaired and must be replaced.
A technician should test the compressor's electrical connections systematically — checking the capacitor with a capacitance meter, inspecting all wiring and connectors, testing the contactor contacts, and measuring the resistance across the compressor motor terminals. If the motor windings are open, compressor replacement is necessary.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Failed compressor motor winding or bad run capacitor | Most common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- The outdoor unit does not start and the furnace shows E405
- You hear a click from the contactor but the compressor does not run
- The outdoor unit's fan runs but the compressor is silent
✓ Verified against manufacturer service manual — March 2026