It should turn around smoothly, without any 'hickups' (be sure to completely shut down the air compressor!). Check the isolation of the motor windings. Should be in the mage-ohms (you need an isolation tester / high voltage ohm meter for this). Check the voltage when the compressor is running.
[pdf] After around 20,000 hours or four years of operation, screw air compressors usually require major maintenance, including bearing replacement. Long-term operation leads to internal bearing wear, causing loud noise and high temperatures. These signs indicate the need for an overhaul.
[pdf] Regular maintenance helps avoid these issues, reducing operational costs, energy consumption, and improving overall productivity. Daily Maintenance Inspection: Before each use, check for loose bolts, proper belt tension, and sufficient oil levels.
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