A pressure relief valve is a safety device designed to protect the compressor from over - pressure situations. Its primary function is to open automatically when the pressure inside the compressor reaches a pre - set limit, allowing excess air to escape and reducing the pressure back to a safe level.
[pdf] 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. If the voltage drop significantly when the compressor starts/runs, you have a bad connection somewhere.
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