MPA Logo, San Francisco Maritime National Park Association, USS Pampanito, Historic Ships at Hyde Street Pier, Education Programs Maritime Park Association Home Page Maritime Park Association Home Page Events Maritime Park Association Home Page Maritime Park Association Home Page Maritime Park Association Home Page Volunteer Membership Donate Maritime Park Association Home Page USS Pampanito Submarine Historic Ships at Hyde Street Pier Education Programs About Maritime Park Association Home Page Directions to Maritime Jobs at Maritime Facility Rental at Maritime Trustees of the Association Calendar Press Room Store Maritime Map
8
OPERATION AND TROUBLES
 
A. REFRIGERATION OPERATING DATA
 
8A1. Low-pressure side. Evaporator data: 1) gage pressure from 2 to 20 pounds; 2) temperature from -10 degrees F to 20 degrees F.

8A2. High-pressure side. Condenser data: 1) gage pressure approximately 105 psi; 2) temperature 93 degrees F; at condenser cooling water temperature 83 degrees F.

8A3. Condenser water flow. 1) Ten gallons per minute per refrigeration ton of 85 degrees F water; 2) a suction pressure corresponding to a temperature of -5 degrees F.

  8A4. Low-pressure cutout. 1) Cutout at 2 psi; 2) cutin at 15 to 20 psi; 3) about 18 psi differential.

8A5. High-pressure cutout. 1) Cutin at 125 psi; 2) cutout at 150 psi. 8A6. Thermostat settings (approximate).

a) Refrigerator room: 1) cutout at 15 degrees F;

2) cutin at 20 degrees F.

b) Cool room: 1) cutout at 38 degrees F; 2) cutin at 40 degrees F.

 
B. OPERATION
 
8B1. Stopping the compressor. When stop ping the system, the procedure varies according to the length of the shutdown. A short shutdown is a period up to four hours. If the shutdown is for a longer period-for example, overnight-the oil in the crankcase absorbs Freon 12 and a special starting procedure is necessary.

8B2. Shutting down for a short period. In shutting down for a short period, proceed in the following manner:

1. Remove the cap nut on the suction stop valve with the special wrench.

2. Rack off slightly on the packing gland nut. This relieves pressure on the gland and also reduces friction wear when the valve stem is worked.

3. With the wrench on the valve stem, slightly close the suction stop valve. The decrease in suction pressure slowly opens the low-pressure cutout switch.

4. When the motor stops, press the STOP button on the main compressor switch. This prevents the system from restarting accidentally.

5. Close the compressor discharge stop valve. This closes off the compressor from the rest of the system.

6. Close the receiver outlet valve. This traps most of the Freon 12 in the receiver and keeps it there during the shutdown.

  7. Close the valves that control the cooling water in the condenser. It is not necessary to stop the condenser circulating water pump since the pump motor is wired in parallel with the compressor motor and stops when the compressor is stopped.

8B3. Starting after a short shutdown. The starting procedure after a short shutdown is the reverse of the stopping procedure.

1. Always check the oil level before starting the compressor. The oil level should be 1/2 to 3/4 high in the oil sight glass. If, it is low, add oil to bring it up to the proper level. If the oil level is high, the oil may contain Freon 12 which evaporates after the compressor has run for a while.

CAUTION. Never start the compressor when the entire crankcase is full. The resulting pressure would cause serious damage.

2. If the oil is at its proper level, open the condenser water supply valve.

3. Open the compressor discharge stop valve.

4. Open the receiver outlet valve.

5. Turn the compressor flywheel over several times by hand. This clears the cylinder of any oil and liquid Freon 12 that may have collected during the shutdown.

6. Start the compressor at the main switch.

7. With the compressor running, slowly open the compressor suction stop valve.

 
53

Watch the suction pressure gage dial and avoid rapid changes in pressure. When the suction stop valve is completely open, the system is in normal operation and under the control of the automatic mechanisms.

8. Tighten the packing gland nut and replace the cap nut on the suction stop valve.

9. Open the vents on the water side of the condenser to allow any air that might be present to escape.

10. Close the vents.

NOTE. On some installations, continuous vents are installed, in which case Steps 4 and 10 are not necessary.

8B4. Starting after a long shutdown. After a long shutdown, overnight or longer, the crankcase may appear to be filled with oil. This indicates that a considerable amount of Freon 12 has been absorbed by the oil while the compressor was not running. Damage is likely if the compressor is started in this condition. Therefore, some of the oil and Freon 12 mixture must be pumped out of the crankcase before starting. The procedure for this operation is as follows:

1. Close the compressor suction stop valve.

2. Connect a 3/8-inch line between the suction pressure gage stop valve and the crankcase oil drain stop valve.

3. Open the suction pressure gage stop valve and the oil drain stop valve.

4. Slowly turn the compressor flywheel by hand. Do not start the compressor motor. Keep turning the compressor by hand until the oil level can be seen in the sight glass.

5. Close the suction pressure gage stop valve and the oil drain stop valve.

6. Disconnect the 3/8-inch line from the compressor.

  7. Now start the compressor according to the procedure given in Section 8B3. As the system operates, the Freon 12 separates from the oil and remains in the system. The oil that has been pumped out of the crankcase returns to it.

8B5. Shutting down for a long period. Shutting down for a long period is sometimes called pumping down, since the procedure pumps most of the Freon 12 out of the coils of the evaporator and stores it in the receiver. Pumping down should be done whenever the plant is taken out of service overnight or longer.

1. Wedge the low-pressure cutout switch. This prevents the motor from stopping when the pressure drops below the normal setting.

2. Close the receiver outlet valve. The compressor now draws most of the refrigerant out of the liquid line and the evaporator and places it in the receiver.

3. When the suction pressure reaches zero, push the STOP button on the control panel.

4. Close the compressor suction and discharge stop valves.

5. Close the condenser water supply valves.

6. When restarting, do not forget to remove the wedge from the low-pressure cutout switch.

8B6. Operating difficulties. Faulty operation of the system is indicated by definite symptoms. These symptoms may be caused by one or more incorrect conditions which must be eliminated in a step-by-step process of methods of correction. The following chart of symptoms, their causes and correctives, assists the operator in correcting faulty operation quickly and efficiently.

 
54

TROUBLE DIAGNOSIS CHART
SYMPTOM CONDITION MAY BE CAUSED BY CORRECTION
High head pressure 1. Air or noncondensable gas in system

2. Inlet warm water

3. Insufficient water flowing through condenser

4. Condenser clogged or scaled up

5. Too much liquid in receiver, condenser tubes submerged in liquid refrigerant

1. Purge air from condenser

2. Increase quantity of condensing water

3. Increase quantity of water

4. Clean condenser tubes

5. Draw off liquid into service drum

Low head pressure 1. Too much water flowing through condenser

2. Water too cold, unthrottled

3. Loose thermal bulb

4. Leaky discharge valve

1. Reduce quantity of water

2. Reduce quantity of water

3. Check and tighten thermal bulb

4. Remove head, examine valve diaphragm; replace if found defective

High Suction pressure 1. Overfeeding of expansion valve

2. Leaky suction or discharge valve

3. Hand bypass open or, if in use in place of expansion valve, open too much

1. Regulate expansion valve; check bulb attachment

2. Remove head, examine valve disks; replace if worn

3. Check hand bypass valve

Low suction pressure 1. Restricted liquid line and expansion valve or suction screens

2. Insufficient gas in system

3. Moisture in system, causing freezing of expansion valve

4. Too much oil circulating in system

5. Improper adjustment of expansion valves

6. 1/4-inch or more frost on evaporator coils

1. Pump down, remove, examine, and clean screens

2. Check for gas shortage

3. Wrap hot cloths around expansion valve and cycle through dehydrator

4. Check for too much oil in circulation; remove oil

5. Adjust valves to give greater flow

6. Defrost

 
55

TROUBLE DIAGNOSIS CHART (Continued)
SYMPTOM CONDITION MAY BE CAUSED BY CORRECTION
Compressor short cycles (on high-pressure cutout) 1. Insufficient water flowing through condenser, clogged condenser cutout

2. High-pressure cutout incorrectly set

3. System overcharged with refrigerant

1. Determine if water has been secured; check for scaled or fouled condenser

2. Check setting of high-pressure cutout

3. High-pressure cutout may be tripping as a result of insufficient condenser capacity because tubes are submerged

Compressor short cycles (on low-pressure cutout) 1. Coils in refrigerators clogged with frost

2. Liquid, suction, or expansion valve screens clogged

3. Thermal bulb on expansion valve has lost charge

1. Defrost coils

2. Pump down and clean screen

3. Detach thermal bulb from suction line and hold in palm of one hand with the other hand gripping the suction line; if flooding through is observed, bulb has not lost its charge; if no flooding through is noticed, replace expansion valve

Compressor runs continuously 1. Shortage of refrigerants

2. Discharge valve leaks badly

1. Test refrigerant; if short of liquid, add amount necessary; test for leaks

2. Remove head of compressor, and repair or replace valves

Compressor noisy 1. Vibration because not bolted to foundation rigidly

2. Too much oil in circulation, causing hydraulic knock

3. Slugging due to flooding back of refrigerant

4. Wear of parts such as piston pins, bearings, etc.

5. Flywheel loose

1. Bolt down rigidly

2. Check oil level

3. Expansion valve open too wide, close; thermal bulb incorrectly placed or loose, check

4. Determine location of cause; repair or replace compressor

5. Check key, tighten flywheel nut

 
56

TROUBLE DIAGNOSIS CHART (Continued)
SYMPTOM CONDITION MAY BE CAUSED BY CORRECTION
Compressor will not start 1. Overload tripped, fuses blown

2. Switch out

3. No charge of liquid in system operated by low-pressure control

4. Dirt or foreign matter on control points of either high- or low-pressure cutouts

1. Reset overload, replace fuses and examine for cause of condition

2. Throw in switch

3. With no liquid in system, there is insufficient pressure to throw in low-pressure control; recharge system with liquid; stop leaks

4. Check and clean points

Head gasket leaks 1. Head bolts stretched, or washers crushed 1. Examine gaskets, replace if necessary; tighten head bolts; replace washers
Cylinders and crankcase sweating 1. Too much oil in circulation; too much refrigerant in circulation

2. Hand bypass valve open or, if in use in place of expansion valve, open too much

1. Examine for conditions of refrigerant and oil charge; correct anything wrong

2. Check hand bypass valve

 
8E7. Electric system. As electric energy is a main factor in refrigeration, a good service man should have a working knowledge of the electrical controls, their functions, how they are energized, and what voltage and amperage they carry. However, this does not imply that the auxiliary man should attempt electrical repairs. This work should be accomplished under the supervision of the electrical department.

Main power for refrigeration and air-conditioning systems is controlled from the auxiliary board in the control room. This switch energizes both systems through two 30-ampere fuses to the refrigeration control panel in the pump room and through four 60-ampere fuses, two for each unit, to the air conditioning system.

When electric current reaches the starter

  box in the pump room, it is divided into two branches: one branch goes through the three steps on the starter, then to the motor of the compressor; the other branch goes through the starter control side of the panel through two separate fuses. The current from these fuses goes through a selector switch that can be set to operate the plant either manually or automatically. When this switch is on automatic, the current passes through a number of controls that are wired in series with each other. These controls are as follows: from selector switch to and through the holding-in coils of the starter, through the low-pressure cutout, and high-pressure cutout. Therefore, any of these controls, or a burned-out holding-in coil can stop the compressor. The selector switch is so made that it makes a number of contacts with only two positions.
 
57

 
C. DEFROSTING
 
8C1. Defrosting the refrigerating room. As in a household refrigerator, the cooling coils of a submarine refrigeration room gradually accumulate a covering of frost from moisture in the air condensing and freezing on the coils. Frost acts as a heat insulator, reducing the cooling efficiency of the system and requiring longer running of the compressor. Therefore, this frost must be removed periodically, and defrosting is one of the important routine operations.

The refrigeration room evaporator is the one that frosts. The cool room evaporator coils normally are not cold enough to frost.

Defrost as often as necessary. Never let more than 1/8 to 1/4 inch of frost accumulate on the coils. Defrosting is simple and should be done frequently.

For defrosting, a special piping connection that conveys hot vapor from the compressor to the evaporator is used. This special piping branches off from the discharge line between compressor and condenser, goes through the wall of the refrigerator room, and connects to the suction line at the outlet of the evaporator coils, where shutoff valves are provided. Defrosting is done while the system is running. The hot vapor introduced into the coils melts the frost in less than half an hour.

See Figure 7-1 for location of valves referred to by letter in the procedure for defrosting, which is as follows

1. Close the king valve on the receiver, and pump the system down to about 5 psi.

  2. Stop the compressor. 3. Close the liquid supply valves (A, B, and L).

4. Open the liquid supply valves (K, D, and E).

5. Open the hot vapor line valves (C) and the suction shutoff valve (M).

6. Close the suction shutoff valve. (J).

7. Start the compressor.

Part of the hot vapor flows through the valve (C) into the refrigerator room evaporator. This evaporator then acts as a condenser and the vapor condenses at a temperature high enough to melt the frost. The refrigerant passes as a liquid through valves (K) and (D) to the expansion valve on the cool room evaporator and enters the cool room evaporator coils in the normal way. That is, the Freon 12 is now a liquid and in the cool room evaporator it boils off, changes to a vapor, and goes through valve (M) back to the suction side of the compressor.

The ice tuber should be left in a normal operating condition, and should not be de frosted when defrosting the refrigerating room. The hatch of the cool room should be left open during defrosting operations, so that an abundance of heat is supplied to the cool room evaporator to insure a complete boiling off of the liquid refrigerant in the evaporator. When all the frost is off the refrigerator room coils, restore the system to regular operation.

8C2. Defrosting the ice tuber. To defrost the ice tuber, close the liquid supply valve and the suction valve. Open the door of the ice tuber.

 
58

Previous chapter
Previous Chapter
Sub Refrig. Home Page
Sub Refrig. Home Page
Next chapter
Next chapter


Copyright © 2013, Maritime Park Association
All Rights Reserved
Legal Notices and Privacy Policy
Version 1.10, 22 Oct 04