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. If the voltage drop significantly when the compressor starts/runs, you have a bad connection somewhere. Check all relays, fuses and electrical connections.
[pdf] Continuous full-load operation (load rate>90%) accelerates component wear and may shorten life to 6-8 years. Reasonably control the load rate (recommended 70%-85%), and avoid frequent starts and stops through frequency conversion control or air tank adjustment.
[pdf] According to screw compressor manufacturers, treatment is closing the ball valve to verify that the rated pressure can be attained and inspecting the air compressor component to prevent issues with that component constituting the treatment procedure.
[pdf] 
