Cummins/Onan — Automatic Demand Control Will Not Start Generator Set With Load

Testing & diagnosis

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

1. Battery terminals may be incorrect. Should have negative ground only.
2. Check cranking limiter relay K3. If tripped, push reset button after waiting one minute. Before restarting, check for cause.
3. Check 6-1/4 ampere fuse. If open, check for short circuit. Remedy and replace fuse.
4. Check if bilge is operating. If it is, wait until the end of bilge blower operation to see if unit starts.
5. If bilge blower does not operate when load is connected, see Bilge Blower Does Not Operate When Load is Connected.
6. If bilge blower doesn't stop after approximately five minutes, check for voltage at relay K4 terminals 85 and 86. If voltage is present, replace relay K4. If voltage is absent, replace time delay rela
7. For HA controllers with time delay preheat, engine cranking is delayed an additional twenty seconds after bilge blower operation. If engine doesn't crank after approximately twenty seconds, check for
8. Check generator set operation without automatic demand control. Disconnect demand control from generator set. Start generator set with set controls. If unit doesn't operate properly, reconnect demand
9. Jumper cranking limiter relay terminal 3 to TB1-3, then remove jumper. Remove quickly if unit starts.
10. Remove the load, stop the generator set, and disconnect battery ground cable. With an ohmmeter, check for continuity across contactor K2 normally-closed contacts (terminals 3 and 4).

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.

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