is to provide the chilled water for the air-conditioning
SEAWATER FAILURE SWITCH.-- T h e
seawater failure switch should be set to close at 15 psig
system throughout the ship. Ships of this class have a
and open at 5 psig.
minimum of three identical units installed.
FRESHWATER FAILURE SWITCH.--The
The compressor is a reciprocating, single-acting
freshwater failure switch should be set to close at 45 psig
unit. It is equipped with a capacity control system, a
and open at 3 psig.
pressure relief valve, and an oil pressure failure switch.
WATER CHILLER OPERATING THERMO-
STATS.-- The water chiller operating thermostats are
Control Devices
set to close when the chilled water reaches 44F and
open when the water temperature reaches 40F.
The operation and pressure setting of the individual
LOW-LIMIT THERMOSTATS.-- The low-limit
control devices are discussed separately in this section
thermostats are backup thermostats for the chiller
to help you understand the operation of the 80-ton
operating thermostat. If the chilled water temperature
air-conditioning unit.
would decrease below the 40F level, the low-limit
thermostat would open at 36F. The low-limit
OIL PRESSURE SAFETY SWITCH.-- The oil
thermostat will not close until the chilled water
pressure safety switch protects the compressor in case
temperature rises to 40F. The compressor operation
of insufficient oil pressure. The switch is wired to the
would not begin until the chiller operating thermostat
compressor motor controller to stop the compressor if
contacts close.
one of the following situations exists:
1. The oil pressure drops to 12 psi or less during
Operation
operation
2. The oil pressure at start-up does not build to a
To help you understand the following discussion of
satisfactory minimum of 18 psi.
the operation of the air-conditioning compressor, refer
to the wiring diagram in figure 5-12.
The oil pressure safety switch is interlocked with a
time delay relay in the motor controller to permit a short
The compressor can only be energized from the
operating period (10 to 15 seconds) at start-up to allow
motor controller, which is located near the equipment.
the oil pressure to develop. The switch is wired so that
Besides providing Start/stop operation of the unit, the
controller has a two-position selector switch, labeled
when the compressor is stopped by the loss of oil
LOCAL or LOCAL/REMOTE. When in the
pressure action, it must be restarted at the motor
LOCAL/REMOTE position, the compressor can be
controller.
stopped remotely by the use of the emergency (EM) stop
SOLENOID VALVE.-- The solenoid valve is a
button located in the control console room.
pilot-operated, piston-type valve and is operated by an
To start the compressor, turn the selectors witch to
electric coil. The valve is open when the current is on
the LOCAL or LOCAL/REMOTE position and press
and closed when the current is secured The solenoid
the start button. This will energize the UV relay,
valve is wired to the water chiller operating thermostat
provided contacts OL, WFS1 and 2, HP, and LT are
for control with the system in operation. The solenoid
closed The W relay will close its UV-1 contacts,
valve shuts when chilled water reaches the minimum
which are connected across the start switch and is the
temperature.
maintaining circuit for the UV relay. At the same
instant, the UV-2 contacts close energizing the 1CR
HIGH-PRESSURE CONTROL SWITCH.--
relay, closing its 1CR-1 maintaining contacts. Also,
The high-pressure control switch should be set to open
UV-3 contacts will close, energizing the timing relay
at 160 psig and close at 140 psig.
(TR). This closes the TR-IC contacts, energizing the
M-coil contactor. Contacts M-1, M-2, and M-3 will also
LOW-PRESSURE SUCTION SWITCH.-- The
close, connecting the motor across the line. Contacts
low-pressure suction switch should be set to close at 40
M4 close to energize the remote run light in the control
console.
psig and open at 20 psig.
5-24
