Marathon Motor Troubleshooting

Marathon Motor Troubleshooting
Motor Troubleshooting
Turn off power at the electrical
service entrance fuse or breaker box before
touching motor or removing cover.
Motor won’t start. No hum, no sound.
No power.
Check fuse or circuit breaker.
No power to motor.
Check power connection. Check for loose connections. Apply power, check voltage at motor terminals with voltmeter.
Turn power
off again at the electrical service entrance fuse or
breaker box before proceeding. Check motor overload continuity. See winding problem below.
Motor won’t start. Hums.
Locked bearings.
Uncouple pump and spin motor shaft. Check for
tight pump seal, obstruction in pump housing or
bad bearing.
Incorrect connections.
Check motor connection diagram. Check control
circuit diagram.
Low voltage
Motor terminal voltage must be within + or – 10%
of nameplate voltage.
Excessive load.
Clogged pump impeller. Bent shaft or bad bearing.
Winding problem.
Check for short, open or ground in winding, lead
connections or winding to motor housing.
Start switch open.
Switch should be closed at standstill. Check
continuity across contacts.
Start capacitor failure.
White residue probably means faulty capacitor.
Loose capacitor connections.
Visual inspection.
Note: “Capacitor Trouble Shooting Procedure” on page 21.
Excessive noise, vibration.
Defective motor bearings.
Spin unloaded shaft, check noise.
Loose or binding parts.
Visual inspection of pump and motor.
Bent shaft.
Remove motor and check shaft run-out.
Start switch doesn’t open.
Start/stop, start/stop, if motor noise disappears,
switch may be defective.
Motor hot, smoking or cycling.
Motor overloaded.
Full-load current greater than nameplate can mean
excessive pump load.
Clogged air openings.
Visual/manual inspection.
Voltage too high/low.
Must be within + or – 10%.
Incorrect connection.
Check nameplate and control diagrams.
Winding shorted or grounded.
Check winding for damage. Check for ground condition. Measure winding resistance.
Start switch fails to open.
Check for welded contacts. Check for broken mech
spring. Replace switch.
Run capacitor failure.
Bulged capacitor indicates failure.
Hot or noisy bearings.
Endshields loose or cocked.
Check through-bolts for tightness. Check frame-toendshield rabbet fit. Spin motor shaft, should turn
Bent shaft.
Measure shaft run-out (straightness).
Defective bearing.
Spin shaft, check for noise, endplay.
Capacitor Troubleshooting
1. To check capacitor ohmmeter, remove all power
from the motor.
2. Use insulated screwdriver to discharge capacitor
by shorting across terminals.
3. Set ohmmeter to highest value, put clips on
capacitor terminals.
4. Check for the following indications:
a. Needle drops to zero range and slowly rises,
capacitor probably good.
b. Needle drops and stays at zero, capacitor
probably shorted.
c. Needle remains at high value, capacitor
probably has open circuit.
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