Generac GT-990 — Generator Tests Under Load
Testing & diagnosis
For the Generac GT-990, from the Generac owner's manual.
Applies to: Generac GT-990 engine
Before you start
- Proceed with caution; generator power voltage is supplied to the transfer switch.
Procedure
- Set main circuit breaker to OFF and turn OFF all loads at T1 and T2.
- Set AUTO/OFF/MANUAL switch to OFF and turn OFF utility power to transfer switch.
- Manually set transfer switch to the STANDBY position.
- Set AUTO/OFF/MANUAL switch to MANUAL; engine cranks and starts.
- Let the engine stabilize and warm up for a few minutes.
- Set main circuit breaker to ON; loads are powered by the generator.
- Turn ON electrical loads equal to full rated capacity.
- Check E1-E2 voltage greater than 230 volts and frequency greater than 58 Hertz.
- Run at full rated load for 20-30 minutes, listening for unusual noise and checking for oil leaks.
- Turn OFF electrical loads and set main circuit breaker to OFF.
- Let engine run at no-load for a few minutes then set switch to OFF.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Voltage should be greater than 230 volts
- Frequency should be greater than 58 Hertz
Source: Generac owner's manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.