No response when start button is pressed, or motor hums and trips.
1
No incoming power
highCheckVerify voltage at disconnect L1-L2-L3 with meter. All legs within ±10% of nameplate.
FixRestore power; check upstream breaker, fuses, and main disconnect.
ToolsMultimeter (CAT III 600V+) · Insulated gloves
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2
Tripped overload relay
highCheckCheck OL reset on starter; look for thermal trip indicator/flag.
FixReset; investigate root cause (high amps, single-phasing, low voltage, mechanical bind).
ToolsMultimeter · Clamp meter
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3
Pressure switch open (system at cut-out pressure)
Reciprocating
CheckBleed tank below cut-in pressure; listen for switch click.
FixIf no click, replace pressure switch. Verify diaphragm and contacts.
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4
Pressure switch unloader stuck
Reciprocating
CheckListen for air bleed on shutdown (should hear 1–2 sec of bleed).
FixClean or replace unloader valve in pressure switch.
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5
Faulty contactor coil
CheckMeasure 24/120/240V at coil terminals when start signal is present.
FixIf voltage present but no pull-in, replace contactor.
ToolsMultimeter
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6
Control transformer fuse blown
highCheckContinuity across control fuse; check secondary voltage at X1-X2.
FixReplace fuse; find the short that blew it before re-energizing.
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7
Emergency stop / interlock open
criticalCheckTrace control wiring; check door interlocks, high-temp switch, oil-level switch, low-oil-pressure switch.
FixReset/repair failed interlock. Do NOT bypass safety interlocks.
SafetyNever jumper a safety interlock to get a machine running.
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8
Controller fault not cleared
Rotary screw
CheckCheck HMI / controller for active fault code. Cross-reference manual.
FixClear fault after addressing root cause. Note repeat faults — they indicate a real problem.
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9
Phase monitor relay tripped (3Φ)
Rotary screw
CheckLED on phase monitor; check all three line voltages and phase rotation.
FixRestore correct phase sequence; replace relay if defective.
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10
Remote start signal missing
Rotary screw
CheckCheck sequencer / building management remote-start contact closure.
FixSwitch to LOCAL mode to bypass, or restore remote signal.
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Safety
Lockout/tagout before opening enclosures. Verify zero energy. Bleed system pressure before opening any pneumatic connection.