Lennox
Failed Capacitor or Stalled Motor
Lennox air conditioner makes loud buzzing or humming at the outdoor unit when trying to start, but fan and/or compressor do not run.
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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, Seized condenser fan motor, Locked rotor compressor, Low line voltage causing stall
How to Fix / Troubleshooting
Safety: Turn off power at the disconnect. Capacitors can hold a charge; discharge properly before handling.
- 1. Inspect capacitor: Look for bulging top, oil leakage, or rust. Replace with the exact Lennox-specified µF and voltage rating if any defect is seen.
- 2. Test fan blade: With power off, spin the fan blade by hand. If stiff or grinding, the motor bearings may be seized and the motor should be replaced.
- 3. Listen for compressor hum: A loud hum from the compressor with no start suggests a locked rotor. A technician can test current draw and possibly install a hard-start kit.
- 4. Check supply voltage: Have an electrician verify proper voltage at the unit; low voltage can cause motors to stall and buzz.
Warning: Do not push the fan blade to start the motor with power on; this is dangerous and only masks the real problem.
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Repair Difficulty
Hard
4/5
Required Part
Lennox Dual Run Capacitor
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