Cummins/Onan — Testing Field Windings for an Open Circuit
Testing & diagnosis
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan MCCK
Procedure
- Disconnect the external leads and connect the ohmmeter leads to F1 (+) and F2 (-).
- At 70°F (21°C), resistance should be 28.8 ohms (±3%) for the BF and 38 ohms (±3%) for the NH.
- Using a continuity tester, touch the test prods to F1 and F2; the lamp should light or buzzer should sound.
- If not, the field winding is open and must be replaced.
- Check the terminal ends closely for loose connections.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 28.8 ohms ±3% (BF) at 70°F (21°C)
- 38 ohms ±3% (NH) at 70°F (21°C)
Full service-parts list: Cummins/Onan MCCK →
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.