Commercial Refrigeration Service Technician Study Guide - 2007 Flashcards
1
Q
In a refrigeration system heat is rejected by
A
latent heat of condensation in the condenser
2
Q
All refrigerants have flammability and the toxicity classifications. Where
could a technician best find those ratings?
A
Compressor
3
Q
The main function of an expansion device is to?
A
Meter the refrigerant
4
Q
The main function of an expansion device is to?
A
Store excess refrigerant
5
Q
How does a technician determine whether or not there is liquid refrigerant
leaving the evaporator?
A
calculates what the evaporator superheat
6
Q
Which of the following is NOT TRUE about refrigerant as it enters the
condenser?
A
it is subcooled
7
Q
Any additional heat added to the refrigerant after its 100% saturated vapor
condition is called?
A
Superheat
8
Q
Most of the heat absorbed in the low side of a refrigeration system is.
A
latent heat
9
Q
If a technician subtracted liquid line temperature from high side
condensing temperature he would
A
Subcooling
10
Q
An azeotropic refrigerant would be defined as
A
a mixture of two or more refrigerants that have the same
boiling point and act as
11
Q
When a zeotropic refrigerant blend changes phase the refrigerants in the
blend have different boiling points which can cause the refrigerant to
A
fractionate
12
Q
A refrigerant that is not miscible with mineral oil is
A
R-404A
13
Q
Which lubricant is most commonly used with HFC-134a refrigerant?
A
polyolester
14
Q
Polyol Ester oils are?
A
hygroscopic
15
Q
Refrigerant tanks must always be stored in an area where the temperature
will not exceed
A
125º F
16
Q
When transferring refrigerants from a cylinder to a working system or any
other container, the technician should always wear
A
goggles with side shields and gloves
17
Q
When entering a mechanical room where a refrigerant leak is suspected
the technician should?
A
use the appropriate breathing apparatus until the area has
been cleared of fumes
18
Q
Which of the following gasses is non flammable and would be preferred
when leak testing a system?
A
CO2 & Nitrogen
19
Q
Refrigerant cylinders that are labeled “Disposable”
A
by law cannot be refilled & are color-coded for easy identification
20
Q
A refrigerant cylinder that has been DOT approved for refilling must
A
never be filled over 80% capacity
21
Q
When calculating how much refrigerant can be placed into a rechargeable
cylinder,
A
tare lbs
22
Q
All refrigerants have flammability and the toxicity classifications. Where
could a technician best find those ratings?
A
the MSDS
23
Q
Double suction riser are used in refrigeration system when
A
large fluctuations in system capacity will occur
24
Q
Suction risers are typically reduced by one size over that of the main
suction run
A
to increase refrigerant velocity to aid in proper oil return
25
When soldering a copper pipe connection which of the following
processes allow
for alloy to be draw into the space between copper pipe and the fitting
connection?
capillary action
26
Before proceeding to make any braze connection in a refrigeration system
all of the internal piping should be purged of atmosphere with
CO2 & Nitrogen
27
The liquid receiver is located between the?
condenser and the expansion device
28
Which device is used in a refrigeration system to protect the compressor
from liquid slugs?
suction accumulator
29
Which device is used to stop the flow of liquid or vapor in a refrigeration
system?
solenoid valve
30
Why is it important to know the direction that a scroll compressor is
rotating?
it will only pump refrigeration in one direction of rotation
31
An electric motor that has a voltage rating of 120 volts will have an upper
and lower allowable voltage limit of
108 to 132 V
32
On a fully welded hermetic compressor the electrical start components are
located
on the external of the compressor at the terminal box
33
On most hermetically sealed compressors
he motor and pumping mechanism are cooled by refrigerant
| vapor
34
The difference between oil pump discharge pressure and crankcase
pressure on
net oil pressure
35
The amount of space between the piston at top-dead-center and the
bottom
clearance volume
36
The flapper valve design is less efficient than the discus valve design
because
the cylinder has more clearance volume than the discus
37
Liquid refrigerant entering the compressor is potentially more damaging
for this type of compressor over the others listed
reciprocating
38
Discus, ring, and flapper valves are not used on
Screw and Scroll Compressors
39
The main function of a condenser in a refrigeration system is?
reject the heat that is absorbed in the evaporator
40
The shell and tube condenser is a type of
water cooled condenser
41
One of the main disadvantages of a water-cooled condenser is that
mineral deposits
insulator
42
A flow regulating valve could be used on this type of condenser
shell and tube
Tube in Tube
43
On a water cooled condenser the water leaving the condenser is normally
______ lower than the condensing temperature of the unit
10º F
44
On a standard efficiency air-cooled condenser the ambient air entering the
condenser will be approximately ________ lower than the condensing
30º F
45
A head pressure control system would be used on this type of application
A. unit located in a colder climate but only operating in summer
unit located in a colder climate operating all year
46
What type of expansion valve regulates its flow based from suction line
superheat?
TXV
47
Systems where the pressure drop across the evaporator is excessive
would typically use a/an.
externally equalized TXV
48
On a system equipped with a TXV, when the load on an evaporator
decreases.
the TXV decreases the flow of refrigerant
49
When referring to a power head on an expansion device the bulb is
normally charged with a fluid similar to that of the system refrigerant
50
By subtracting the low side evaporator outlet temperature from the low
side
evaporator superheat
51
On a typically evaporator employing a TXV the liquid refrigerant should be
completely boiled to a vapor?
near the evaporator outlet
52
What type of TXV would be best for an application that was exposed to
fluctuating ambient temperatures?
balanced port TXVs
53
Pressure-limiting TXV’s are generally applied on systems when
it is necessary to shut off the refrigerant flow to the evaporator when the suction pressure reaches a predetermined pressure.
54
Which of the following is not true regarding the evaporator in a
refrigeration system?
it rejects heat from the conditioned space
55
Heat that is added to the refrigerant stream after the 100% saturated
vapor point is called?
superheat
56
Multiple refrigerant circuits are preferred on evaporators that are?
Large or long
57
In a system where the evaporator temperature operators above 32º F the
technician needs to be concerned with?
The system would not need a method of defrost since the coil would not collect frost
58
The fin spacing per inch on a medium-temperature evaporator is
closer together than on low-temperature evaporator
59
A refrigeration system that utilizes two or three stages of low temperature
refrigeration
is called a cascade refrigeration system
60
When leak testing a refrigeration system using a high pressure nitrogen
tank the technician should always
use a pressure regulator and safety relief value at the nitrogen
tank
61
The maximum pressure that can be applied to a refrigeration system when
pressure testing is
determined by the systems rated nameplate test pressures
62
The safest way to charge refrigerant into a system that is running is with
vapor into the low side
63
When heating a refrigerant cylinder the technician should never use
any type of open flame
64
Refrigeration systems must be fully evacuated before charging with
refrigerant
to remove air and moisture from the system
65
A vacuum pump will lose its ability to draw a deep vacuum over time
because
the oil becomes full of moisture and acids which will decrease the capability of the vacuum pump
66
A refrigerant service valve must be placed in the
mid position in order for the technician to access the system
67
When using a micron gauge to measure vacuum the system should be
evacuated to a level of _____ to ensure that non condensables and
moisture have been adequately removed
500 microns
68
Amperage is a measure of
electron flow
69
Voltage is the measure of
electrical pressure
70
Wattage is a measure of
electrical power
71
746 watts equals
1 horsepower
72
One kilowatt is equal to
3412 Btus
73
The unit of measurement for magnetic flux is?
maxwell
74
On a resistive electrical circuit which law would be used to calculate I, E or
R?
Ohm’s
75
Which of the following formula would be used to calculate amperage in
resistive circuit?
I=RE
76
Capacitance represents a components ability to
store electrons
77
A meter with the capacity to measure very high resistances is call a?
megger
78
A technician would use a micron gauge to measure?
deep vacuum
79
If a technician has set his VOM meter to R x 100 he would be measuring
resistance
80
When checking resistance through a motor winding the proper instruments
to use would be a/an?
ohmmeter
81
An ohmmeter will measure infinite resistance when testing an
Open Fuse & Open contacts
82
If a technician has placed his VOM in parallel with an energized load he is
probably checking?
voltage
83
When a technician is checking unknown _______ he should always set
the instrument to the highest scale to prevent damage to the meter.
Voltage & Amperage
84
If a technician has placed his VOM in series with the load he is probably
checking?
Amperage
85
Which of the following instruments would be used to check the condition of
insulation on a motors windings?
megohmmeter
86
A ladder diagram can also be called
electrical line wiring diagram
87
A pictorial diagram will?
show approximate location of electrical system components
88
The primary and secondary windings in a transformer are wired in?
not connected electrically
89
What happens when the length of the path of an electrical circuit is
decreased?
there will be a decrease in total circuit resistance
90
What is the total amperage of a circuit when two 25 ohm resistors are
connected in series using a 120 volt power source?
2.4 amps
91
If the voltage is the same across each load in a circuit it would be
considered?
parallel circuit
92
If a circuit is designed to allow the flow of electrons to follow only one path
it would be?
rectifier circuit
93
A line or ladder type diagram is most useful for?
understanding circuit operation
94
If a technician took a reading across a normally closed set of contacts
when a relay or contactor coil was de-energized the reading would be?
0 volts
95
An ohmmeter must never be connected to a
energized circuit
96
If a 24 volt control transformer has a VA rating of 60 what is the maximum
amperage rating?
2.5 amp
97
A technician has obtained the following resistance readings across the
terminals on a single phase compressor: 8 ohms from T1 to T3, 3 ohms
from T1 to T2, and 5 ohms from T2 to T3. Which terminals are RUN,
START, and COMMON?
T1 is Run
T2 is Common
T3 is Start
98
The contacts of a current relay
are normally open contacts
99
A motor starter is also called a?
motor controller
100
If a relay coil is open the technician would read ______ when checking if
with his ohmmeter
Infinite resistance & zero resistance
101
A sensor that uses a positive temperature coefficient thermistor (PTCT)
increases resistance as temperature increases
102
These devices are used to protect electrical circuits from overcurrent
fuses and breakers
103
If two 30 µf run capacitors are wired in parallel what is the new microfarad
rating on the circuit?
60 µf
104
On a hermetic compressor what component is designed into the
| compressor to protect against excessive temperatures and overcurrent
an overload protector
105
The contacts of a potential relay
are normally closed
106
A rectifier is used to?
convert alternating current to direct current
107
The run windings of a motor have _____ turns as compared to the start
windings.
fewer
108
On a typical split-phase electric motor the start winding circuit is deenergized as it
reaches approximately ____ of its operating speed?
75%
109
What component wired in series with the start windings on a single phase
motor will create greater starting torque.
a capacitor
110
A three-phase motor does not have
start windings
a start capacitor
a start relay
111
A start component that is rated in microfarad would be a
capacitor
112
What effect will a higher supply voltage have on the current draw of an
electric motor?
it will be higher than it should be
113
With an electric motor running normally the amperage reading would be
called?
run-load amperage
114
If a technician uses an ohm meter to check the windings of an electric
motor and records an infinite reading on the start windings this would
indicate?
the start winding circuit has an open somewhere
115
What device would be discharged using a 20,000-ohm, 5 watt resistor?
capacitor
116
The run-load amperage on an electric motor is typically
1/5 that of a full-load amperage
117
What device is used to energize another load such as a contactor or motor
starter with in turn would start or stop a motor.
a pilot duty relay
118
A magnetic coil and electrical contacts are the primary components of this
electrical device?
a contactor
119
A magnetic coil, overload protector and electrical contactors are the
primary components of this electrical device
a motor starter
120
An electric motor that has an internal overload would have a?
a thermal device buried in the motor windings
121
What device could be used as external protection for a motor?
a line fuse
a circuit breaker
an external overload
122
What type of motor would a technician switch any two legs on to reverse
the rotation of the motor?
Three Phase
123
A technician could install this type of component on a refrigeration system
that has multiplexed circuits to
prevent the evaporator temperature on a multiplexed system
| from falling too low
124
A technician would set this device by the RLA on the refrigeration
compressors
crankcase pressure regulator
125
A technician would set this device by calculating the evaporator
superheat.
thermal expansion device
126
What device is used to reduce the suction temperature of the
| compressor?
desuperheating TXV
127
If a technician needs to control the head pressure on a refrigeration unit
within tight limits the best device to employ on the condenser fan motor
would be?
a variable frequency drive (VFD)
128
The EPR valve is installed between the?
suction accumulator and the compressor
evaporator and the suction accumulator
129
Which of these devices would be considered a low ambient temperature
head pressure control used on an outdoor unit?
fan cycling
130
If a technician wanted to protect a refrigeration system from operating
under excessive head pressure situations he would install a/an
head pressure control
131
The following device would use a pressure transducer to sense net oil
pressure, electronic oil safety controllers use a
electronic oil safety contro
132
If a technician needed high accuracy it would be best to select a device
that employed the following sensing element if available
a thermistor
133
If a technician installed a low-pressure switch, a liquid line solenoid valve,
and a thermostat in a
refrigeration system what kind of circuit would have been designed?
automatic pump down cycle
134
.
.
135
.
.
136
.
.
137
.
.
138
.
.
139
Large or small compressors on parallel compressor racks, which are
usually dedicated to the coldest cases, are called?
satellite & booster compressors
140
What is a true statement regarding the operation of a parallel rack
system?
it allows for better temperature control than a single condensing unit
it allows for multiple evaporator temperatures to be maintained
it allows for greater operational safety versus a single condensing
141
Why is it important for the oil separator to be sized properly, insulated and
located as close to the compressor as possible?
to minimize the chances for refrigerant vapor to condense into
liquid inside the separator
142
The capacity that a parallel rack will have during operation is determined
by?
the coldest temperature evaporator
143
On a parallel compressor rack what device is used to control multiple
evaporators?
EPR.
144
What can cause the suction pressure on a parallel rack system to run
higher than its setpoint?
a higher than design system load
145
Auxiliary contacts would not be used to?
Control a crankcase heater
Control an interlock circuit
146
What device would be used to cycle the condenser fans on and off as
system head pressure changes?
a reverse acting high-pressure control
147
A device used to damper out compressor torque to the connected copper
piping is a
vibration eliminator
148
A device used to maintain a minimum oil condition in a parallel rack
compressor is
oil level contro
149
To maintain the correct amount of oil in each compressor on a parallel
rack an oil system would
oil separator
oil reservoir
oil level regulator
150
What device is used on an oil system on a parallel to control the pressure
of the oil feeding the
oil regulator?
pressure differential valve
151
What is the best method for precharging an oil separator?
charge the oil directly into the separator before brazing into
place
152
A decrease in suction pressure of a reciprocating compressor will result in:
a decrease in volumetric efficiency
153
For every 1ºF of additional liquid subcooling a systems capacity will be
increased by approximately?
1%
154
These lines should be insulated to help maintain subcooling
liquid line
155
Additional liquid subcooling
reduces the amount of flash gas at the outlet of the TXV
156
What is the purpose of a mechanical subcooling loop on a parallel rack
system?
reduce the temperature of the liquid entering the metering device
on the system being subcooled
ncrease the capacity of system to which the liquid is being
subcooled
157
Inadequate liquid sub cooling in a system can cause?
excessively high evaporator superheat
excessively high discharge temperatures
158
What device would be considered a non-modulating expansion device?
a capillary tube
159
A CPR valve is used to protect the compressor from?
high load pull-downs
amperage load over RLA
160
What happens to the gauges if there is a high refrigerant charge in a
system using a capillary tube?
both the suction and discharge gauges will indicate a high
| pressure
161
An overcharge with this type of device will cause a decrease in evaporator
superheat?
capillary tube
162
The liquid receiver service valve could be used to?
charge refrigerant into the system
remove refrigerant for the system
stop the flow of refrigerant for system pump down purposes
163
A technician me need to bypass this control when charge a system
LPC
164
When charging liquid refrigerant into a compressor care must be taken
because?
damage to the compressor may occur by liquid slugging
it is easier to overcharge the system
165
Low suction pressure and under cooling can be caused by?
undercharged system
166
What type of refrigerants must be charged into a system in a liquid form?
zeotropic refrigerants
near azetropic refrigerants
167
A low pressure switch can be used to?
control frost build-up on the coil
168
What device is used to shut the compressor off if the suction falls below a
given set point?
LPC
169
What device is used to prevent refrigerant migration to the compressor
during the off cycle?
a crankcase heater
a pump-down cycle
170
On an ice machine the flush cycle is designed to?
remove mineral build-up in the water
171
Carbon filtration is used to?
remove chemicals from the water
172
The flaky coating that can build up on the surface of the evaporator on an
ice machine is called?
scale
173
How is the ice harvest accomplished on most ice machine?
by hot gas defrost
174
What could cause an ice machines capacity in #’s per hour to be reduced?
excessive mineral deposits on the evaporator plate
dirty condenser coil
higher than normal entering water temperature
175
Sand and dirt in water are usually easily removed by?
filters
176
As its temperature decreases, a/an ____ will decreases its resistance.
PTC thermistor
177
What type of valve is used to direct hot gas from the condenser to the
reclaim coil?
a three way heat reclaim valve
178
What is the media that is heated by a heat reclaim system?
Air & Water
179
Why is a heat reclaim system so important?
it allows heat to be recaptured from the refrigerant stream and
reused.
180
What is the function of a timer release solenoid?
terminate the defrost cycle
181
What component energizes the electric defrost heater on a 24-hour
defrost timer?
a normally open set of contactors
182
On an electric defrost system what device initiates the de-energizing of the
heater if the evaporator temp rises above freezing before the timed defrost
cycle ends?
termination thermostat
183
What would the best method of defrost be for a fixture that has a case
temperature below freezing and is operated by a single condensing unit
located in a low ambient condition?
electric defrost
184
What is the BTU output of an electric defrost heater that is rated at 1200
watts?
4096 BTU’s
185
What would the best method of defrost be for a fixture that had an
evaporator temperature below freezing but a case temperature above
freezing?
off cycle air defrost
186
On a supermarket rack employing hot gas defrost where would the hot
gas solenoid valve be installed?
between the discharge line and the oil separator
187
If you find yourself at odds with a confrontational customer, you should
keep your cool, learn as much as possible about the
customer’s complaint, continue working if possible, but call
your supervisor to report the incident
188
When entering a customer residential premises you should always
place a clean pair of disposable covers over your shoes
189
If the technician is on a service call and notices another potential problem
not related to the current work order, what should the technician do?
discuss what you have found with the customer and your supervisor so that the
customer can decide whether to authorize the additional repair
190
Which of the following is a required part of the work order?
form completed in legible hand writing
complete list of materials used and amount of time spent on the job
191
Getting the customer to sign the work order should be
the last thing that you should do before leaving the job
192
Which of the following is a part of your responsibility relative to your work
crew?
working safely on the worksite
193
You are called to a job site to perform some maintenance work on a
system and after you are finished the customer approaches you and offers
to pay you cash directly to perform some additional work. In this situation it
would be ok to?
refuse the offer politely and if it happens again notify your supervisor of the situation
194
What should the technician do in a situation where he is working on a
refrigeration system that operates a case that holds perishable food items,
the compressor has failed, it is 5:00 on a Monday evening, and it will take
a few additional hours to repair the rack?
request authorization from the customer to stay on the job until it is finished that evening
