The screw element is seizing -- bearings are worn, oil is gone, or something is mechanically wrong. The motor can't turn it without drawing excessive current.
What you'll see
If the element turns freely by hand, the binding might be intermittent (hot seizure when oil thins) or the overload could be caused by electrical issues. See: Voltage Drop, Phase Loss, Worn Relay.
How to diagnose
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Try to turn the element by hand
Disconnect power, remove fuses for safety. Try to rotate the motor shaft or coupling by hand. A healthy element turns smoothly with no high points or rough spots. Screw element bearing life is approximately 40,000 running hours.Result: Can't turn or feels rough = bearing failure or oil starvation. -
Check oil level and condition
If the oil is gone or looks like tar, the bearings may have run dry. This is the most common cause of airend seizure.Result: No oil or severely degraded oil = oil starvation caused the damage.
How to fix it
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Airend rebuild or replacement
A seized airend needs professional rebuilding (new bearings, possible rotor resurfacing) or complete replacement. This is the most expensive repair on a screw compressor. Prevention through proper oil maintenance is far cheaper.
Don't keep resetting the overload and restarting when the element is binding. Each attempt puts enormous stress on the motor and can burn out the windings, turning one expensive repair into two.
Airend rebuild kit or replacement airend. This is a specialist repair.
Disconnect power completely before trying to turn the element by hand. If the airend is seized, do not force it -- you'll damage the rotors further.
This issue can also cause
- Unusual Noise Abnormal sounds like grinding, knocking, squealing, or rattling during operation, typically indicating bearing...