Cummins/Onan — Generator Set Starts But Stops When Line Contactor Pulls In
Testing & diagnosis · Start-Run Relay K9, Current Transformer CT1, Load Sensor Board A1
From a Cummins/Onan service manual covering: 15.0 HA, 15.0HA-23/24D, 15.0HA-23/25D, 7.5 HA, 7.5HA-21/24D, 7.5HA-21/25D, 7.5HA-23/24D, 7.5HA-23/25D. Check it applies to your exact model before use.
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Procedure
- Move Auto-Manual switch to Manual position. Start generator set at unit controls by placing the switch to Start position. Controller contactor should close and supply power to load.
- Place HA control Auto-Manual switch to Auto position. If generator set stops, review the following:
- A. Remove start-run relay K9 and perform a continuity check between pins 1 and 8 to check resistance of holding coil. Reading should be 500 ohms ±10%. Replace relay if defective.
- B. Perform continuity check of current transformer lead connections at A1/J1 (pins 7,8 and 9).
- C. Replace load sensor board A1.
- Generator set repeatedly over-cranks and trips cranking limiter K3. Check fuel level and standpipe depth in tank.
Tools required
- ohmmeter Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 500 ohms ±10%
Source: Cummins/Onan service 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.