Cummins/Onan — Testing Reference Transformer
Testing & diagnosis · Reference Transformer T21
From a Cummins/Onan service manual covering: JC 15.0, JC15, MDJC 10.0, MDJE 75, MJC15. Check it applies to your exact model before use.
Applies to: Cummins/Onan MDJC, Cummins/Onan MDJE, Cummins/Onan MDJF
Procedure
- Resistance between H1-H2 should be 122 to 150-ohms.
- Resistance between X1-X2 should be 157 to 192-ohms.
- Resistance between H1-X1, H1-X2, H2-X1 and H2-X2 should be infinity.
- Resistance from any terminal to transformer frame should be infinity.
- If any condition is not met, install a new reference transformer.
Tools required
- ohmmeter Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- 122 to 150-ohms
- 157 to 192-ohms
- infinity
Full service-parts list: Cummins/Onan MDJC →, Cummins/Onan MDJE →, Cummins/Onan MDJF →
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.