Modern Refrigeration and Air Conditioning, 19th Edition Page 471 (493 of 1488)

Chapter 19 Installation and Troubleshooting of Domestic Refrigerators and Freezers
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The location of the adjustment screws and the adjust-
ment procedure varies from model to model. Always
check the service manual of the equipment being
serviced.
19.4.2 Identifying Common Problems
The following are common conditions that can
develop inside a system and negatively affect its per-
formance. Being familiar with these common prob-
lems will help a technician effectively diagnose and
repair a malfunctioning system.
The presence of a restriction can be checked by
looking at the high-side and low-side pressures. If a
restriction is present at the metering device, the high-
side pressure will be very high, and the low-side pres-
sure will be very low. For example, an R-134a system that
normally operates with a suction pressure of 5–10 psig
and head pressure of 150 psig may have a vacuum on the
low side and a head pressure over 200 psig.
Moisture in the Refrigerant Circuit
Moisture in the refrigerant system will cause
a unit to malfunction. The moisture forms ice in the
metering device at the point where liquid refrigerant is
expanding into the evaporator. Ice closes the opening,
blocking flow into the evaporator. This condition can
be recognized by the following symptoms:
• If the system is completely defrosted, the ice that
caused the blockage disappears. The unit will
then work properly again. However, the unit will
only work until ice again forms at the metering
device.
• Pressure decreases in the suction line. The
compound gauge shows a steady decrease over
several hours (even to a vacuum). Then, pressure
suddenly becomes normal again. This odd cycle
will keep repeating.
• Warm the metering device with a safe resistance
heater (hot pad) or radiant heat bulb during system
shutdown to melt any ice build-up. If the system
then begins to work properly, there is definitely
moisture in the refrigerant.
Moisture in the refrigerant circuit also creates cor-
rosion problems within the system. This occurs when
refrigerants react with water molecules to form acids.
The acids increase the amount of corrosion in the sys-
tem. Excessive moisture in the system indicates that the
filter-drier is clogged. Refer to Chapter 20, Service and
Repair of Domestic Refrigerators and Freezers, for informa-
tion about replacing filter-driers.
There are certain substances that can be placed
in the refrigerant circuit to keep moisture from
forming ice. However, a filter-drier is the best solution.
It prevents circulation of the moisture through the
system. It also reduces the chance of oil breakdown,
which results in sludge and acid.
Wax
Manufacturers have removed as much wax as pos-
sible from refrigeration oil, but some wax still remains.
Some oil circulates with the refrigerant. Sudden
expansion at the refrigerant control, accompanied by
low temperature and pressure, causes some wax to
separate from the oil. The wax collects in the metering
device. In time, it may build up sufficiently to restrict
flow or completely clog the metering device.
If there is a restriction in the metering device,
it should be determined whether the restriction
is caused by wax or ice. If the metering device is
clogged with ice, it may be fixed by installing a new
filter-drier, as explained in the previous section. If
the metering device is clogged with wax, both the
metering device and the filter-drier must be replaced.
Procedures for replacing metering devices are pre-
sented in Chapter 20, Service and Repair of Domestic
Refrigerators and Freezers.
Shortage of Refrigerant
A shortage of refrigerant is another common
cause of poor refrigeration. If a shortage of refriger-
ant is found, there is often a leak. Small systems have
only one or two pounds of refrigerant. Therefore, even
the smallest leak will soon cause poor refrigeration.
A leak with a loss rate as low as one ounce per year can
be located and must be repaired. The following condi-
tions indicate a lack of refrigerant:
• The low-side pressure is below normal.
• The outlet end of the evaporator is warm.
• The high-side pressure is below normal.
19.4.3 Diagnosing Specifi c
Component Problems
Before removing any system component, be cer-
tain that it is the cause of the problem. After diagnos-
ing the system by visual inspection and by analyzing
system performance, perform pinpoint tests of the sus-
pected components before replacing them. The follow-
ing are parts that frequently cause trouble:
• Compressor.
• Filter-drier.
• Metering device (capillary tube or AEV).
• Hot-gas defrosting valve.

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Extracted Text (may have errors)

Chapter 19 Installation and Troubleshooting of Domestic Refrigerators and Freezers
471
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
The location of the adjustment screws and the adjust-
ment procedure varies from model to model. Always
check the service manual of the equipment being
serviced.
19.4.2 Identifying Common Problems
The following are common conditions that can
develop inside a system and negatively affect its per-
formance. Being familiar with these common prob-
lems will help a technician effectively diagnose and
repair a malfunctioning system.
The presence of a restriction can be checked by
looking at the high-side and low-side pressures. If a
restriction is present at the metering device, the high-
side pressure will be very high, and the low-side pres-
sure will be very low. For example, an R-134a system that
normally operates with a suction pressure of 5–10 psig
and head pressure of 150 psig may have a vacuum on the
low side and a head pressure over 200 psig.
Moisture in the Refrigerant Circuit
Moisture in the refrigerant system will cause
a unit to malfunction. The moisture forms ice in the
metering device at the point where liquid refrigerant is
expanding into the evaporator. Ice closes the opening,
blocking flow into the evaporator. This condition can
be recognized by the following symptoms:
• If the system is completely defrosted, the ice that
caused the blockage disappears. The unit will
then work properly again. However, the unit will
only work until ice again forms at the metering
device.
• Pressure decreases in the suction line. The
compound gauge shows a steady decrease over
several hours (even to a vacuum). Then, pressure
suddenly becomes normal again. This odd cycle
will keep repeating.
• Warm the metering device with a safe resistance
heater (hot pad) or radiant heat bulb during system
shutdown to melt any ice build-up. If the system
then begins to work properly, there is definitely
moisture in the refrigerant.
Moisture in the refrigerant circuit also creates cor-
rosion problems within the system. This occurs when
refrigerants react with water molecules to form acids.
The acids increase the amount of corrosion in the sys-
tem. Excessive moisture in the system indicates that the
filter-drier is clogged. Refer to Chapter 20, Service and
Repair of Domestic Refrigerators and Freezers, for informa-
tion about replacing filter-driers.
There are certain substances that can be placed
in the refrigerant circuit to keep moisture from
forming ice. However, a filter-drier is the best solution.
It prevents circulation of the moisture through the
system. It also reduces the chance of oil breakdown,
which results in sludge and acid.
Wax
Manufacturers have removed as much wax as pos-
sible from refrigeration oil, but some wax still remains.
Some oil circulates with the refrigerant. Sudden
expansion at the refrigerant control, accompanied by
low temperature and pressure, causes some wax to
separate from the oil. The wax collects in the metering
device. In time, it may build up sufficiently to restrict
flow or completely clog the metering device.
If there is a restriction in the metering device,
it should be determined whether the restriction
is caused by wax or ice. If the metering device is
clogged with ice, it may be fixed by installing a new
filter-drier, as explained in the previous section. If
the metering device is clogged with wax, both the
metering device and the filter-drier must be replaced.
Procedures for replacing metering devices are pre-
sented in Chapter 20, Service and Repair of Domestic
Refrigerators and Freezers.
Shortage of Refrigerant
A shortage of refrigerant is another common
cause of poor refrigeration. If a shortage of refriger-
ant is found, there is often a leak. Small systems have
only one or two pounds of refrigerant. Therefore, even
the smallest leak will soon cause poor refrigeration.
A leak with a loss rate as low as one ounce per year can
be located and must be repaired. The following condi-
tions indicate a lack of refrigerant:
• The low-side pressure is below normal.
• The outlet end of the evaporator is warm.
• The high-side pressure is below normal.
19.4.3 Diagnosing Specifi c
Component Problems
Before removing any system component, be cer-
tain that it is the cause of the problem. After diagnos-
ing the system by visual inspection and by analyzing
system performance, perform pinpoint tests of the sus-
pected components before replacing them. The follow-
ing are parts that frequently cause trouble:
• Compressor.
• Filter-drier.
• Metering device (capillary tube or AEV).
• Hot-gas defrosting valve.

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472
Modern Refrigeration and Air Conditioning
Locating Compressor Faults
The most expensive service item for a domestic
refrigerator is the replacement of the compressor. The
technician should carefully check for all other electri-
cal and mechanical failures before determining that
the compressor needs replacement. When a compres-
sor is in good condition, the most common reason for
replacement is an electrical fault.
Other electrical problems often mislead a ser-
vice technician into thinking the motor compressor
is at fault. To check a motor compressor, first discon-
nect power to the unit and then clean the outside of
the compressor dome. Then, remove the cover over the
electrical connections. Disconnect the system wiring
from the compressor: relay, capacitors, overload cutout,
and all. Use an ohmmeter to check motor windings for
continuity, shorts, and grounds. Refer to Chapter 14,
Servicing Electric Motors and Controls. If the unit checks
out correctly, connect a starting circuit to the motor
compressor. Use the correct size of capacitors and over-
load cutout. Connect the starting circuit as shown in
Figure 19-26.
If the system starts and operates correctly with
these manual-start electrical connections, the problem
is in the external system. It may be in the wiring, ther-
mostat, relay, or overload cutout. If the internal electri-
cal motor is faulty, the compressor must be replaced. If
the electrical system operates correctly, the compressor
may not be pumping.
The best check of the compressor is its volt-ampere
(watt) reading at normal low-side and high-side pres-
sures. If the volt-ampere reading is below the motor’s
rating, the pump may be worn out.
If the compressor is operating correctly but not
building up pressure, check for internal problems
with the compressor. To check the compressor’s pump-
ing ability, install a piercing valve on the suction line
and attach a compound gauge or the compound gauge
Overload
protection
C
R
S
W
G
B
Starting
switch
Starting
capacitor
High-pressure vapor Low-pressure vapor
High-pressure liquid Low-pressure liquid
Goodheart-Willcox Publisher
Figure 19-26. To test a capacitor-start motor compressor, remove all electrical leads and then connect a test cord as shown. If the
motor compressor operates properly when manually started, the problem is external.

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470
Modern Refrigeration and Air Conditioning
As the handle is turned, the ball bearing presses
into the tubing and compresses it against the die on the
bottom of the tool. A permanently pinched line is pro-
duced. See Figure 19-24. Care must be taken to avoid
over tightening the pinch-off tool. The tool should be
left in place until the tubing end is sealed by brazing.
Effect of Altitude on Refrigerator Temperatures
A refrigeration system with a sensing bulb ther-
mostat calibrated for use at sea level may run too
cold at elevations above 5000′. This is a result of the
decreased atmospheric pressure at higher elevations.
Changes in altitude do not affect bimetal and elec-
tronic thermostats.
As altitude rises, atmospheric pressure drops.
Beyond certain elevations, the reduced atmospheric
pressure lowers the pressure on the control diaphragm
or bellows enough to affect the settings. The altitude
adjustment and range control pressure for the bellows
or diaphragm should be increased if the system will be
operating at a high elevation. This adjustment compen-
sates for the lower atmospheric pressure.
Figure 19-25 shows one thermostat with an alti-
tude adjustment and its altitude adjustment table. To
adjust for altitude, the cut-in and cut-out adjustment
screws are turned the appropriate number of degrees.
Ritchie Engineering – YELLOW JACKET Products Division
Figure 19-22. Two styles of pinch-off tools. A—This type
of pinch-off tool resembles and operates like locking pliers.
B—On this type of pinch-off tool, the wing nuts are loosened.
The tubing is inserted through the rectangular jaws in the
center of the tool. The wing nuts are then tightened to deform
and seal the tubing.
Tubing Ball bearing
Goodheart-Willcox Publisher
Figure 19-23. Ball bearing–type pinch-off tool.
A
B
Inner tubing
wall
Original tubing
shape
Goodheart-Willcox Publisher
Figure 19-24. Deformations created by pinch-off tools.
A—Pinch-off made by the tools shown in Figure 19-22.
B—Pinch-off by a ball bearing–type pinch-off tool.
00
55
50
45
35
30
For altitude correction, both “cut-in” and “cut-out”
screws must be adjusted
Adjustment
Altitude
in Feet
Cold
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
10,000
This scale may be used as a guide for measuring degrees of
rotation required for altitude correction. The arrows indicate
direction of screw rotation.
7/60
13/60
19/60
25/60
31/60
37/60
43/60
49/60
55/60
Counterclockwise
Turns
25
20
15
10
5
40
Amana Refrigeration, Inc.
Figure 19-25. Thermostat equipped with an altitude adjustment.
The table indicates the correct setting for various elevations.

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Page 3Section 1 Refrigeration System Fundamentals click to expand contents

Page 43Section 2 Service Basics click to expand contents

Page 109Section 3 Refrigerants click to expand contents

Page 199Section 4 Basic Electricity, Magnetism, and Electronics click to expand contents

Page 251Section 5 Motors and Electric Control Systems click to expand contents

Page 337Section 6 Compressors, Valves, and Metering Devices click to expand contents

Page 411Section 7 Domestic Refrigerators and Freezers click to expand contents

Page 499Section 8 Indoor Air Fundamentals click to expand contents

Page 603Section 9 Air-Conditioning Systems click to expand contents

Page 769Section 10 Heating Systems click to expand contents

Page 957Section 11 Energy Management and Conservation click to expand contents

Page 1007Section 12 Commercial Refrigeration Systems click to expand contents

Page 1177Section 13 Designing Commercial Refrigeration Systems click to expand contents

Page 1227Section 14 Installing and Servicing Commercial Systems click to expand contents

Page 1343Section 15 Professional Development click to expand contents

Extracted Text (may have errors)

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