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.
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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
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.
