Cummins/Onan — Contactor Pilot-Relay Coil Resistor Adjustment

Adjustments · Pilot relay K4 and resistor R4

From a Cummins/Onan service manual — check it applies to your exact model before use.

Browse Cummins/Onan generators & specs →

Procedure

1. Open the cabinet door; move the operation selector switch to STOP; disconnect the starting battery ground cable.
2. Remove all AC power from the automatic transfer switch.
3. Remove the disconnect plug and open the control panel.
4. Remove the wire lead(s) on the side of resistor R4 and the lead(s) on the side of relay K4 coil; connect an Onan Multi-Tester, or a Variac and accurate voltmeter, to the resistor and relay.
5. If the automatic transfer switch operates on 240, 480, or 600 volts, also connect a step-up transformer (minimum 25 VA).
6. If the resistor was replaced, set the slide on the new resistor approximately the same as the one removed; if just the relay was replaced, do not move the slide.
7. Connect the Multi-Tester or Variac to a 120-volt AC source.
8. Vary the voltage from 0 to rated voltage; at approximately 85 to 90 percent of rated voltage relay K4 contacts should close.
9. If setting is incorrect, remove AC voltage and move the slide on resistor R4 a small amount (increasing resistance causes relay K4 to energize at higher voltage).
10. Repeat the voltage variation and slide adjustment until the correct resistor setting is obtained.
11. Remove AC voltage, then disconnect and remove the voltmeter and Multi-Tester or Variac.
12. Reconnect the wire leads to resistor R4 and relay K4, close the control panel, and reconnect the disconnect plug.
13. Restore AC line voltage and connect the battery ground cables.
14. Move the operation selector switch to RMT or AUTO, whichever applies, and close the cabinet door.

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.

More Cummins/Onan repair guides →