The key is to test the contactor in a logical order instead of jumping straight to replacement. Always begin with lockout/tagout and voltage verification. Use this troubleshooting guide if your power is not applied on your load after supplying your contactors coil. It has two main parts: a coil, which creates a magnetic field when electricity flows through it, and contacts, which open or close the circuit. When the coil is energized, it moves the contacts to connect or. To test a contactor properly, start with the simplest checks first: isolate power, inspect the device visually, verify the coil circuit, check contact continuity, and then confirm switching behavior under the correct control conditions. UDC and INVudc come up and the VCU goes into RUN mode.