Underfrequency
Generac
Generator frequency below nominal
Controller logs 'Underfrequency' alarm; frequency measured at output is below 60 Hz (or 50 Hz) even at no load.
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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
Engine running below rated RPM, Governor misadjustment, Fuel starvation, Faulty frequency sensing circuit
How to Fix / Troubleshooting
Safety: Disconnect generator from load before testing. Use a frequency meter or multimeter with Hz function.
- Measure frequency and RPM: With the generator running in MANUAL and no load, measure frequency at the output and RPM at the engine. If both are low, focus on engine/gov issues.
- Adjust governor: Follow Generac service procedures to adjust the governor to achieve correct no-load RPM and frequency. Do not exceed rated RPM.
- Check fuel system: Inspect filters, regulators, and gas supply for restrictions that could limit engine power.
- Controller sensing: If mechanical speed is correct but the controller still reports Underfrequency, inspect the sensing leads and control board. Replace the controller if sensing circuits are faulty.
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Repair Difficulty
Medium
3/5
Required Part
Governor Linkage
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