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.

Defrosting

Cooling units in the 35F to 45F 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 35F 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.

ELECTRICAL DEFECTS

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 circuits.

Opens

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 fact - if you are

Figure 6-62. - Simple refrigeration control system.