Armstrong Air
Compressor Hard Start / Locked Rotor
Outdoor unit hums loudly but compressor does not start, then shuts off on overload
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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
Weak or open compressor start winding, Failed start/run capacitor, Low supply voltage, Internal compressor mechanical failure
How to Fix / Troubleshooting
Safety first: Turn off power and discharge capacitors before touching electrical components. Compressors can be extremely hot.
Steps:
- 1. Inspect and test capacitor: Remove and test the dual run capacitor. Replace if more than 10% out of spec or physically damaged.
- 2. Check supply voltage: Have a qualified person verify correct line voltage at the contactor under load.
- 3. Listen for start attempts: After replacing the capacitor, restore power and call for cooling. If the compressor still only hums, it may be locked.
- 4. Do not repeatedly reset: Repeated attempts can permanently damage the compressor.
- 5. Professional evaluation: A technician can attempt a hard-start kit (if appropriate) and measure locked-rotor amps. If the compressor remains locked, replacement of the compressor or outdoor unit is required.
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Repair Difficulty
Professional Required
5/5
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