The OP contacts should close before the TR contacts
As soon as the chilled water temperature rises to or
above the cut-in setting of the operating thermostat, the
open, which are time opening. The unit should operate
solenoid opens and allows liquid refrigerant to flow to
normally and will be stopped and started by the LP
the pilot thermal expansion valve. The pilot supplies
switch.
pressure to the main thermal expansion valve and moves
it to the OPEN position. Liquid refrigerant is thus
During operation, opening the OP, WFS, HP, or LT
allowed to flow to the chiller. The suction pressure rises,
contacts will cause the W relay to be de-energized,
causing the cut-in setting of the low-pressure control
drop out, and stop the motor. The normally closed UV-5
switch to close its contacts. This starts the compressor
interlock contacts will close and complete the circuit to
motor.
the safety shutdown alarm.
Loss of voltage for any reason will cause the UV
SUMMARY
relay and 1CR relays to drop out, stopping the unit. On
restoration of the voltage, you need to press the start
In the previous section, the function and the
button to restore the compressor to normal operation.
equipment used in air conditioning and refrigeration
were described. Also, the operation of air compressors
This feature is known as low-voltage protection
and the refrigeration and air-conditioning systems are
(LVP).
covered. It should be apparent that this equipment is
very important. If you do not understand a system
An overload will cause the OL contacts to open, stop
completely, go back and review before continuing on to
the motor, and energize the alarm. To restore operation,
the next sections.
you will have to press the stop-reset button and then the
start button.
To stop the compressor manually, all you need to do
PENDULUM WINDOW
is press the stop-reset button.
WIPER
The window wiper (fig. 5-13) is an extremely
When the selector switch is in the
simple, rugged piece of equipment. The information in
LOCAL/REMOTE position, the emergency
the following paragraphs will give you enough
(EM-STOP) button in the console is energized. If the
information to enable you to operate, troubleshoot, and
EM-STOP button is pressed for any reason, the ESR1
repair almost any problem that occurs with the wiper.
relay will become energized, which will close its
contacts ESR1-1. This causes the ESR2 relay to be
DESCRIPTION
energized close its maintaining contacts ESR2-1 and
ESR2-2, and open contacts ESR2-3. This sequence
The pendulum window wiper is a variable-speed,
shuts down the compressor. The ESR2-1 contacts are
electric motor-driven oscillating arm wiper with a
only maintaining contacts for the ESR2 relay. The
totally enclosed drive unit. The wiper is equipped with
ESR2-2 contacts will energize the EM-STOP indicating
a heated arm for operation under icing conditions. The
light in the control console.
entire unit weighs 20 pounds and is mounted on the
bulkhead over the window it serves. The wiper is
The OT and solenoid circuit operates to cut in or cut
suitable for use on fixed or hinged windows and can be
out the refrigerant to the pilot thermal expansion valve.
adjusted to ensure correct blade pressure and travel.
This causes the main thermal expansion valve to close,
The window wiper runs on dc voltage. It takes
cutting off the supply of refrigerant to the water chiller.
115-volts, single-phase ac power from the ship's service
With the solenoid valve closed and the supply of liquid
line and rectifies it through a full-wave bridge rectifier.
refrigerant cut off to the chiller, the compressor
continues to operate for a short period of time until the
CONSTRUCTION
suction pressure drops to the cutout setting of the
low-pressure control switch. The switch contacts then
The wiper consists of three major components:
open and the compressor motor stops.
5-26
