1
Open transition timing wrong
CheckTime S→D should be 0.5–2.5 sec typical (per starter).
FixAdjust timer.
2
Wye contactor not dropping out
CheckAux contact wiring; mechanical interlock.
FixReplace contactor / repair interlock — risk of phase-to-phase short.
3
Delta (run) contactor not pulling in
CheckCoil voltage after timer transition.
FixRepair control circuit / replace contactor.
4
Motor leads wired wrong (T1–T6)
CheckVerify per nameplate diagram: T4 to T1+R, T5 to T2+S, T6 to T3+T after delta close.
FixRe-terminate per diagram.
5
OL relay sized wrong for delta connection
CheckHeater = motor FLA × 0.58 (line current in delta winding).
FixResize.
Safety
Lockout/tagout before opening enclosures. Verify zero energy. Bleed system pressure before opening any pneumatic connection.