or removed for adjustment. Latch mechanisms should
be lubricated and adjusted for easy operation. Latch
rollers must not bind when operated. Be sure to
provide sufficient clearance between the body of the
latch and catch, so no contact is made. The only
contact is made between the catch and the latch bolt or
roller. These instructions also apply to safety door
latches, when they are provided for opening the door
from the inside, although it is locked from the outside.
Warping of the door usually causes lack of complete
gasket contact between the door overlap and the
doorframe. Correct the condition by installing a long,
tapered wooden shim or splicer rigidly in place under
the door seal. If this does not tighten the door to the
frame, remove the door and either reline or rebuild it.
Repair or replace missing, worn, warped, or loose
door gaskets. If the gasket is tacked on, rustproof tacks
or staples should be used. If the gasket is clamped or
held in place by the doorframe or the door panel, an
exact replacement is necessary. In either case, the
gasket should be installed so when the door is closed a
complete and uniformly tight seal results. If doors
freeze closed due to condensation and subsequent
freezing, apply a light coat of glycerine on the gaskets.
Cooling units in the 35°F to 45°F reach-in or
walk-in refrigerators or cold storage rooms are
generally defrosted automatically by setting the
low-pressure control switch to a predetermined level.
If this setting causes overload with consequent heavy
frosting of the coil, manual defrosting is necessary.
Cooling units of 35°F and lower temperatures are
defrosted manually. The most common method for
manual defrosting is to spray water over the cooling
coil, although warm air, electric heating, or hot gas
refrigerant defrosts too. In any case, the fans must not
be in operation during the defrosting. Defrost
plate-type evaporator banks in below-freezing
refrigerators when the ice has built up to a thickness of
one-half inch or when the temperature of the fixtures or
the suction pressure is affected by the buildup of ice.
Before removing frost from the plates, place a
tarpaulin on the floor or over the contents of the
refrigerator to catch the frost under the bank.
The control systems for modern refrigeration
systems are composed of many components that use or
pass electrical power, including compressor drive
motors, pressure switches, thermostats, and solenoid
stop valves. Although as a Utilitiesman second class
you are not responsible for troubleshooting these
electrical components, you must be able to use the
multimeter for locating opens, shorts, and grounds,
and measuring voltage and current. Module 3 of the
Navy Electricity and Electronics Training Series,
NAVEDTRA 172-03-00-93 (Introduction to Circuit
Protection, Control, and Measurement), will help you
in learning to use electrical meters and testing
equipment. When you have finished studying the
module, return to this chapter and learn how to locate
opens, shorts, and grounds in refrigeration control
Figure 6-62 shows a simple refrigeration control
system. You have learned the basics of electricity and
how to use meters. Using this figure, you will put that
knowledge to work. Remember one factif you are
Figure 6-62.Simple refrigeration control system.