Cummins/Onan — Testing L21 Reactor
Testing & diagnosis · L21 commutating reactor
From a Cummins/Onan service manual covering: 300.0 DFT, 350.0 DFU, 350.0 WF, 400.0 DFV, 400.0 WK, 450.0 DFW, 500.0 DFY, 600.0 DWV. Check it applies to your exact model before use.
Applies to: Cummins/Onan YB series
Procedure
- L21 mounts inside control box, below VR21 voltage regulator.
- Coils 1-2 and 3-4 are wound on the same core.
- Resistance between 1-2 and 3-4 should be equal.
- Resistance between coils (e.g., 1-4) or from any terminal to frame should be infinity.
Tools required
- ohmmeter Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Resistance between 1-2 and 3-4 equal
- Resistance between coils or to frame infinity
Full service-parts list: Cummins/Onan YB series →
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.