(4M) is normally closed in the de-energized condition,
figure 5-10. To start the compressor, turn the selector
keeping the oil heater energized This contact is opened
switch to LOCAL or NORMAL operation. Then press
by the M coil at the same time that 1M, 2M, and 3M are
the start button. Provided the contacts for OL, WF, and
closed.
DP are closed, the UV relay will be energized and close
its UV-1 contacts across the start switch contacts, which
The suction pressure switch (SP) is connected in
will maintain the holding circuit for the UV relay. At
series with the UV-2 contacts. It is used to sense the
the same time, the UV-2 contacts close, causing the main
pressure of the compressor suction line for automatic
contactor coil (M), the relay (TR), and the elapsed time
operation. The switch stops the compressor when the
meter (ETM) to be energized. This causes the M coil to
pressure is reduced to a level corresponding to the open
close its contacts (1M, 2M, and 3M), and then the motor
setting (5 in. Hg vacuum). The compressor is
should start.
automatically started again when the SP switch contacts
close and the suction line pressure increases to the
The timing relay (TR) is energized and will open its
closed setting (8 psig). The cycle starts over again to
TR-2 contacts after a 10-second time delay. This should
maintain the refrigerated rooms at their normal
allow the oil pressure enough time to increase and close
temperatures.
the oil pressure switch contact (OP). If the oil pressure
does not close its OP contacts, the compressor will stop
If any of the contacts (WF, DP, OP, or OL) open, the
after 10 seconds when the TR-2 contacts open. The
motor will stop and will have to be started manually.
ETM will run only as long as the motor is energized or
running.
80-TON AIR-CONDITIONING UNITS
The IR relay is energized at the time the start button
The function of the 80-ton air-conditioning units
is pushed. It is maintained by the IR-1 contact across
(fig. 5-11) installed on board the FFG-7 class fast frigate
the start switch contact. You will notice that the contact
Figure 5-11.--80-ton compressor unit assembly.
5-23
