d.
An electrical AC hum caused by a defective starting relay.
e.
Obstruction in high velocity air stream can cause rattle or pure tone
whistle.
An air flow noise or hollow whistle type of noise from the clean air plenum when the
compressed air line is opened is an indication of a loose or leaking vent line or fitting
between a diaphragm valve and its pilot solenoid. These are located in the clean air
plenum. The affected valve can be quickly isolated by holding a hand below each of
the blow-pipes until the one leak is located. Follow the black ¼” poly tube line from the
diaphragm valve on the affected blow-pipe back to its pilot valve. Remove, inspect and
re-install the line after checking the tightness of the fittings in both the diaphragm and
the pilot solenoid valves.
