system air pressure. Solenoid valve coil (10) is
deenergized, stopping the air compressor unit from
loading. When system air pressure decreases to
approximately 3000 psig (17225 kPa), (10) closes,
energizing (10) and allowing the air compressor unit to
In the event that the engine should overheat,
cylinder head temperature switch (11) will close. This
will cause safety relay (10) to energize. When (10)
energizes, fuel solenoid valve (13) deenergizes. Fuel
flow to the engine ceases and the engine stops. If
engine oil pressure should fall below 8 ± 1 psig (55 ± 7
kPa), switch (12) will close. This will cause safety relay
(10) to energize. If compressor oil pressure should fall
below 8 ± 1 psig (55 ± 7 kPa), switch (8) will open. With
the LOAD/UNLOAD switch (7) in the LOAD position,
unloader valve (10) will deenergize. When (10)
deenergizes the air compressor unit will continue to
operate but will not load the air receiver.
OPERATING CONTROLS AND INDICATORS.
All controls and indicators necessary for operation of the
air compressor unit are located either on the control
panel or instrument panel. Name plates are provided to
identify all controls and indicators. Identification and
function of each control and indicator is as follows (see
HOURMETER (1, Figure 4-2). The hourmeter
indicates the total number of hours that the compressor
has been operated. A pressure switch closes the
electrical circuit to the hourmeter when the compression
cycle begins. Records of hourmeter indications will be
used to initiate maintenance schedules for performing
service and maintenance functions.
AMMETER (2, Figure 42). The ammeter
indicates the output of the alternator which is used to
change the battery. Under normal operation, the
ammeter will indicate a changing rate of the alternator
varying from zero (0) to a plus (+) 40 amps.
Figure 4-2). The COMPRESSOR OUTPUT INDICATOR
will indicate the PSIG of the compressor output through
the mechanical filter (18, Figure 8-2) immediately
downstream from the 4th stage of the compressor.
SERVICE PRESSURE GAUGE (4, Figure 4-2).
This guage will give the PSIG pressure available at the
compressor unit service outlet (7).
COMPRESSOR OIL PRESSURE GAUGE (5,
Figure 4-2). The COMPRESSOR OIL PRESSURE
gauge indicates air compressor lubricating oil pressure in
pounds per square inch (PSI). Normal air compressor oil
pressure is 25 ± 5 psi
(173 ± 35 kPa). If the compressor oil pressure should
drop below 8 psi + 1 psi (55 kPa ± 6.89 kPa) while
operating, the compressor will shut down and the cause
of low oil pressure should be determined. Refer to
troubleshooting, Table 5-4.
ENGINE OIL PRESSURE GAUGE (6, Figure 4-
2). The ENGINE OIL PRESSURE gauge indicates the
oil pressure present in the engine lubricating system.
Normal operating pressure range is 60 ± 10 psi (414 ±
689 kPa). If engine oil pressure should drop below 8 psi
(55 KPa) while operating the engine will shut down.
SERVICE AIR OUTLET (7, Figure 4-2). The
SERVICE AIR OUTLET is the primary outlet. A servicing
hose is attached to the outlet and storage air tanks as
START SWITCH (8, Figure 4-2). The diesel
engine START SWITCH is a spring-loaded switch that
controls the flow of the electrical current to the starting
motor. When the START SWITCH is pressed it
completes the circuit to the starting motor which in turn
completes a path to ground for the battery allowing the
starting motor to run. When the start switch is released,
it returns to the off position stopping the starting motor.
MASTER SWITCH (9, Figure 4.2). The
MASTER SWITCH is a disconnect switch for the air
compressor unit's electrical system.
THROTTLE CONTROL (10, Figure 4-2). The
ENGINE THROTTLE is connected to the engine
governor, which controls the engine speed from idle to
2,000 rpm (2,000 r/min). Pulling the THROTTLE
CONTROL out raises the engine speed. Turn
THROTTLE CONTROL handle clockwise to hold and
lock engine speed. Turning the handle counterclockwise
unlocks the handle. Push handle in to reduce engine
CLUTCH OPERATING ROD (11, Figure 4-3).
The clutch which connects the diesel engine to the air
compressor, is operated by the CLUTCH operating rod.
The clutch is disengaged when the clutch handle is away
from the instrument panel. Push clutch rod handle
toward instrument panel to engage the clutch.
SERVICE VALVE (12, Figure 4-2). The
SERVICE VALVE controls the flow of breathable air
through the SERVICE OUTLET (7). The SERVICE
VAI.VE (1 2) should be fully open when a receiving unit is
being charged, and closed when the compressor is
building up its working pressure.