Try to turn the compressor by hand. It should be possible to turn it around. It should turn around smoothly, without any 'hickups' (be sure to completely shut down the air compressor!). Check the isolation of the motor windings.
[pdf] The Variable Frequency Rotary Screw Air Compressor is an energy efficient solution for industrial air compression requirements. The motor output frequency is intelligently matched to air consumption, making it more energy efficient and longer lasting than traditional air compressors.
[pdf] Power frequency direct coupling screw type Coaxial integrated structure without any loss, reduce vulnerable parts, high rotation rate. Direct drive coaxial integrated design, dust-proof sound insulation cotton, 70 decibels, protection level IP55, waterproof and dustproof.
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