Lennox
Compressor Start Failure
Outdoor Lennox condenser fan runs but compressor does not start; unit hums or is unusually quiet and no cooling is produced.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Failed dual run capacitor, Locked rotor compressor, Open compressor winding, Loose compressor wiring at contactor or terminal plate
How to Fix / Troubleshooting
Safety: Turn off power at the disconnect and verify with a meter before touching internal components.
- 1. Listen for compressor: If only the fan is running and there is no deeper humming sound, the compressor is not starting.
- 2. Inspect capacitor: Locate the dual run capacitor in the control compartment. If it is bulged, leaking oil, or rusted, it is likely failed and should be replaced with the exact µF and voltage rating.
- 3. Check compressor wiring: Ensure all wires to the compressor terminals and contactor are tight and not burned.
- 4. Hard-start kit (technician): A technician can install a Lennox-approved hard-start kit to assist a marginal compressor in starting, but if windings are damaged, compressor replacement may be required.
Warning: Do not repeatedly force the system to start; this can overheat and permanently damage the compressor.
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Repair Difficulty
Hard
4/5
Required Part
Lennox Dual Run Capacitor
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