Controller displays “Underfrequency” or “Low Hz” and may prevent transfer or drop load; lights may dim when large loads start.

Safety first: Open the generator output breaker and prevent transfer while troubleshooting. Running at low frequency can damage some loads.

Steps:

• Check fuel supply: Confirm gas valves are fully open and that gas pressure is adequate. For LP, ensure tank level is sufficient and regulators are not iced up.
• Inspect air filter: Remove and inspect the air filter element. Replace if dirty or oil-soaked.
• Reduce load: If underfrequency occurs only under heavy load, reduce nonessential loads or re-balance circuits on the Eaton automatic transfer switch.
• Governor inspection: Check the mechanical governor linkage and springs for wear or binding. Replace worn springs and adjust per engine manual to restore correct no-load and full-load speed.
• Retest: After corrections, run the generator and verify frequency with a meter or the controller display (should be near 60 Hz in North America).