7th 6 Months Final Flashcards
1
Q
Refrigeration is the process of ___ the air in a defined space.
A
lowering the temperature of
2
Q
The temperature of a material decreases if the material ____ and nothing else happens that would have the opposite effect.
A
contacts a cooler material
3
Q
The two kinds of air conditioning are
A
comfort and process
4
Q
One of the physical states of matter is
A
gas
5
Q
You can cause matter to change its physical state by
A
adding or removing heat
6
Q
Thermal energy that cannot be detected by a thermometer is called latent heat. Thermal energy that is directly related to the temperature of a material is called ___ heat.
A
sensible
7
Q
A temperature of 45 degrees F is about the same as ___ degrees C.
A
7
8
Q
Heat can be transferred from one place to another by the process of
A
conduction
9
Q
The latent heat of vaporization of a substance is the amount of heat the substance absorbs as it
A
evaporates
10
Q
A refrigeration system has been turned off for several days. It contains both liquid refrigerant and vapor. Suddenly a line containing the refrigerant breaks; what happens inside the system?
A
The pressure decreases
11
Q
From the compressor, refrigerant flows to the
A
condenser
12
Q
The graph below is the pressure-temperature chart for a refrigerant. Point ___ represents a condition of superheating.
A
1
13
Q
Compared to a dry-expansion evaporator, a flooded evaporator of the same size
A
is more efficient
14
Q
The purpose of a cooling medium is to
A
remove heat from compressed refrigerant vapor
15
Q
An automatic expansion valve is a metering device that maintains a constant pressure in the
A
evaporator
16
Q
The properties of air that are important in psychrometrics include
A
enthalpy
17
Q
In a sling psychrometer, the wet-bulb temperature is usually a lower value. If the difference is very small, you know the air is quite
A
humid
18
Q
Air that is saturated is air that is at the
A
dewpoint temperature
19
Q
Relative humidity changes if the ___ changes, but the specific humidity does not.
A
dry-bulb temperature
20
Q
To calculate the enthalpy of a sample of air, you must include
A
latent heat of the water vapor
21
Q
In order to remove the moisture that enters a refrigeration system during repair, you must evacuate the system by using a ___ to make all the moisture vaporize.
A
vacuum pump
22
Q
One useful method of detecting leaks in a refrigeration system involves using an ____ leak detector.
A
electronic
23
Q
Relative humidity can be measured with an
A
hygrometer
24
Q
Which of the following is a correct match between an electrical value and the instrument used to measure it?
A
Resistance; ohmmeter
25
In the list below, identify the line that correctly matches one of the classes of work-area hazards to an example of that class of hazard.
Chemical; container of refrigerant
26
If you increase the pressure of a liquid, its ___ temperature will ____, meaning that it will boil at a higher temperature.
saturation; increase
27
At a temperature of 30 degrees F, the enthalpy of the saturated liquid refrigerant is 3.5 BTU/lb. The enthalpy of evaporation is 87.4 BTU/lb. What is the enthalpy of the saturated vapor?
90.9 BTU/lb
28
In the following diagram of a refrigeration cycle, the line between points ___ represents the amount of subcooling
2 & 3
29
A system must provide 8 tons of refrigeration. What compressor horsepower is needed for this system?
10.3 HP
30
Liquid refrigerant can be sub cooled by transferring heat either to the atmosphere in the condenser or to the ____ in the suction line heat exchanger.
refrigerant vapor
31
An "ideal refrigerant" has which of the following characteristics?
Non-flammable
32
In the ASHRAE standard designations of refrigerants, the
letter R is being replaced by letters identifying the chemical structure.
33
Temperature glide occurs only in ___ refrigerants.
blended
34
ASHRAE classifies refrigerants according to how hazardous they are. The ratings are based on flammability and toxicity of the refrigerants. The most hazardous refrigerants are rated
B3
35
When handling and storing refrigerants, you must protect yourself by
avoiding any open flame
36
The ozone layer in the earth's atmosphere is important because it
absorbs ultraviolet radiation from the sun
37
CFCs released into the atmosphere deplete the ozone layer by breaking apart and releasing chlorine ions that then remove single oxygen atoms from the ozone molecules. CFCs also contribute to the greenhouse effect by
absorbing infrared radiation
38
In order to minimize the release of CFCs into the atmosphere, refrigeration service technicians must
recycle refrigerants on-site, if possible
39
A recycled refrigerant may be placed in
the system from which it was removed
40
During the installation of a new system, the chance of future refrigerant leaks can be reduced by
installing a muffler in the compressor discharge line
41
To reduce the depletion of the ozone layer, the U.S. government has implemented laws requiring the
testing and certification of all technicians whose work can cause the release of harmful refrigerants
42
The EPAs final rule concerning the handling of refrigerants and refrigeration equipment requires
certifying the equipment used in recycling and reclaiming refrigerants
43
The compressor for an active recovery system is part of the ____. The compressor for a passive system is part of the ___.
recovery equipment; system being serviced
44
Which of the following is required by the EPA
Certification activity report
45
Technicians who work on residential air conditioning systems must have at least _____ certification.
Type II
46
Which of the following is a contaminant that can be removed by a filter-drier?
Acid
47
An absorption type desiccant holds water by means of a ___ action, but an adsorption type desiccant holds water by means of a ___ action.
chemical; mechanical
48
If you mount a filter-drier in a vertical suction line, the inlet should be located at the top so that ___ cannot become trapped inside.
oil
49
When selecting a filter-drier, you need to base your selection in part on the
minimum particle size it can trap
50
When installing a filter-drier in a refrigeration system, you should
wear safety goggles
51
You can pinpoint leaks in a new refrigeration system by charging the system with ___ and using a ___
nitrogen; soap solution
52
When preparing to use a gauge manifold in servicing a pressurized refrigeration system, you connect its high-side charging hose to the
compressor discharge service valve
53
To check the charge in a refrigerant system, you can look at the ___ in the liquid line. If the charge is low, you will probably see ___.
sight glass; bubbles
54
In using the deep-vacuum method of dehydrating a refrigeration system, you lower the pressure to about ___ microns or less. With the vacuum pump turned off, a gradual rise in pressure tells you the system is ___.
1,000; not dry
55
You can tell whether you have charged a refrigeration system with the correct amount of refrigerant by checking the
weight of refrigerant used
56
The miscibility of the refrigerant oil is its ability to
mix with the refrigerant
57
Oil that becomes mixed with the refrigerant in a system can cause which of the following problems?
Clogged desiccant
58
An oil separator is located between the ____ an ___ in order to keep oil out of the condenser and evaporator.
compressor; condenser
59
Moisture in a refrigeration system causes a variety of problems, including
blockage in cold parts of the system
60
Before you check the oil level in the sight-glass on a refrigeration compressor, you should stop the compressor for at least ____. The compressor should be ____ while you check the oil level.
ten minutes; stopped
61
A positive-displacement compressor uses a piston or other device to
compress refrigerant vapor in a chamber
62
Which of the following is a kind of kinetic displacement compressor?
centrifugal
63
Which of the following is part of a scroll compressor?
Swing link
64
A multiple stage refrigerant system has more than one
compressor
65
When selecting a replacement compressor, you need to make the replacement will operate (with/at) the proper
discharge pressure
66
Among reciprocating compressors, the crankshaft is usually vertical in a ___ compressor, but horizontal in an ____ compressor
full-hermetic; open
67
On the pistons of reciprocating compressors, the ___ ring(s) prevent oil from reaching the compression chamber. The ___ ring(s) prevent refrigerant from escaping around the piston during compression.
bottom; top
68
Which of the following is a method of distributing lubricating oil in a reciprocating compressor?
Crankshaft splash
69
A cylinder unloader reduces the capacity of a reciprocating compressor by allowing refrigerant to flow through the ___ port during the ___ stroke.
suction; compression
70
One way of reducing vibration problems in reciprocating compressors involves the use of
spring mounts
71
One advantage of rotary compressors over reciprocating compressors is that the
vibration is less
72
Slugging is the entry of ___ refrigerant into a compressor. Cavitation is the formation and collapse of ____ in a liquid flowing under pressure.
liquid; vapor pockets
73
One purpose of the accumulator on a rotary compressor is to
keep dirt and debris out of the compressor
74
Helical compressors differ from rotary compressors in that they have
no vanes
75
In a scroll compressor, one scroll is stationary and the other ____. Refrigerant enters the scrolls at the ___ and leaves at the center.
orbits; outer edge
76
The amount of compression in a centrifugal compressor depends on the ____ the impeller, which depends in turn on the impeller's ___ and rate of rotation
tip speed; diameter
77
In reverse hydrostatic sealing, the flow of ___ across the seal opposes the flow of ____ across the bearing.
refrigerant vapor; oil
78
18
18
79
19
19
80
20
20
81
21
21
82
Which of the following motors can be used in hermetic compressors?
Capacitor start, induction-run
83
You can reverse the direction of a single-phase induction motor by
reversing the connection of either the starting or the running winding
84
To change a dual-voltage motor to run on 240 V instead of 120 V, you need to
connect the two running windings in series
85
A single-phase motor used in a hermetic compressor has a relay to disconnect the starting winding from the circuit when the motor approaches its running speed. One kind of relay operates when the current in the ___ winding falls to a preset value. Another kind operates when the voltage across the ___ winding rises to a preset value.
running; starting
86
Two basic categories of motor starting devices are
contactors and starters
87
A reduced-voltage starter limits the current to the motor at startup in order to prevent
voltage drops to other equipment
88
Overload protection for compressor motors may be provided by an
external bimetallic disk
89
Crankcase heaters are especially useful on compressors that are subjected to
cold climates
90
Installing a suction-line accumulator can protect a compressor from damage caused by
slugging
91
The "first rule" of preventive maintenance for compressors and related components is to
follow the manufacturer's recommended maintenance schedules and procedures
92
Typical preventive maintenance procedures for compressors and related equipment include
listening for unusual noises
93
A compressor may overheat because of a
low oil level
94
When pumping down a compressor for service, run the compressor with the valve on the suction line closed, then close the valve on the discharge line and stop the compressor. Repeat this process until the pressure holds at ___ psig.
+2 to +5
95
After disassembling a reciprocating compressor and cleaning the parts, you should inspect the parts for
excessive wear on the bearing surfaces
96
The capacity of a condenser is affected by the
area of contact with the cooling medium
97
Natural-draft air cooled condensers and forced air condensers are alike in that both types
need 600 to 1200 cfm of air per ton of capacity
98
Low-ambient control in an air cooled condenser can be achieved by
closing the dampers
99
Spring loaded relief valves protect a system against explosion by acting in response to high ___. Fusible plugs act in response to high ___.
pressure; temperature
100
Periodic maintenance of air cooled condensers includes doing which of the following every three months?
checking all belts and pulleys
101
In the ___ system, water passes through the condenser to cool the refrigerant. The water is then ___.
wastewater; discharged to the sewer
102
In a water cooled condenser system, "makeup water" is used for
replacing water lost through evaporation
103
Tube-in-tube, shell-and-coil, and shell-and-tube condensers are alike in the following way
liquid refrigerant collects at the bottom
104
A condenser has a pressure-relief device that ___ if the refrigerant pressure becomes too high.
releases refrigerant
105
Generally, how long should you allow a chemical cleaner to stand in a condenser
a few hours
106
Which of the following can increase the capacity of a cooling tower or a spray pond by the greatest amount?
decrease in dry-bulb temperature of the air
107
What type of cooling tower is shown in the drawing below?
induced draft, counter flow
108
Which components in the water-circulating system for a cooling tower or spray pond are used to keep the concentration of minerals low?
bleed-off valve
109
The capacity of a cooling tower can be controlled by means of a
diverting valve
110
As part of maintaining a cooling tower, you should check the ___ everyday.
float valve for clogging
111
The basic classifications of evaporative condensers are
blow through and draw through
112
An evaporative condenser may include a de-superheating coil for the purpose of
reducing the formation of scale
113
Which of the following methods will maintain condensing pressure during cold weather operation?
circulating water intermittently
114
What will prevent the water in an evaporative condenser from freezing during cold weather?
installing a sump heater
115
As part of maintaining an evaporative condenser, you should check the ___ every three months.
pulleys and belts for wear
116
One of the main categories of water related problems in an air conditioning or refrigeration system is
corrosion
117
Corrosion in a water cooled system can be caused by
biological organisms
118
Scale formation can be reduced in a refrigeration system by adding ___ to the cooling water.
acid
119
Bacteria and algae can be controlled in a refrigeration system by adding ___ to the cooling water.
chlorine
120
Chemical deterioration in a wooden cooling tower can be controlled by
keeping pH of circulating water in the 6.0 to 7.5 range
121
In a cooling system, one of the main lines in the piping system is the ___ line.
liquid
122
Steel pipe is typically joined by means of
flanges
123
Tubing is often preferred over piping in a cooling system because it
absorbs vibration better
124
Refrigeration tubing is typically joined by
soldering
125
When brazing tubing to a fitting, you should first heat the ___ until the ___ melts.
tubing; flux
126
The function of the discharge line in a refrigeration system is to
convey the refrigerant to the condenser
127
The "entrainment" of compressor oil is the ___ the moving refrigerant
drawing and transporting of oil with
128
In order to keep entrained oil droplets moving through the piping, the refrigerant must move at ___ fpm in horizontal piping and ___ fpm in a vertical riser.
500 to 700; 750; to 1,500
129
Refrigerant can be prevented from collecting in the compressor during the off-cycle by installing a ____ in the ___.
check valve; discharge line
130
Accessories often added to a discharge line include a
discharge muffler
131
Sub-cooling is desirable in the liquid line, because it
reduces the volatility of the refrigerant
132
If the pressure in the liquid drops, flash gas can form, which can reduce the
refrigerating effect
133
With halocarbon refrigerants, the movement of oil is better in the liquid line than in the discharge line, because the
oil is miscible in most liquid refrigerants
134
A liquid receiver is used to
store all the refrigerant during repairs
135
The purpose of a solenoid valve in the liquid line is to stop the flow of refrigeration to the
evaporator
136
A double suction riser installed in a cooling system enables the system to operate at maximum load without creating excessive ___ in the suction line.
pressure drop
137
An accumulator in the suction line traps oil and liquid refrigerant to keep it from entering the ___. A heater in the accumulator evaporates the ___.
compressor; refrigerant
138
An evaporator-pressure regulator valve closes part way if the pressure at the evaporator outlet becomes too ___. A crankcase-pressure regulator valve closes part way if the pressure at the compressor inlet becomes too ___.
low; high
139
The suction line is insulated in order to prevent or reduce ___ the line.
condensation on the outside of
140
The amount of oil that can build up in the suction line of an idle single-compressor system is much ___ than the amount that can build up in an idle compressor of a multiple compressor system. To prevent damage from excessive oil buildup, the suction line should include a trap with a minimum rise of ___ in.
less; 14
141
Piping problems that result in operating problems are often caused by
liquid hammer
142
Which of the following expansion joints can be used in a refrigerant line?
Bellows
143
Which kind of support is appropriate for a horizontal piping run 15 feet long?
Rod-type hanger
144
The problems caused by vibration in the piping of a cooling system include
damage to valves and controls
145
Insulation is needed on the liquid line if the line is ___ than its surroundings. The purpose of insulation on the liquid line is to prevent the loss of any ___ of the refrigerant.
much colder; sub-cooling
146
What is the main function of a control system?
maintain a variable at a setpoint
147
What are the basic components of a control system?
Sensor, controller, controlled device
148
Air-conditioning and refrigeration systems are commonly controlled by ___ control.
proportional
149
Which of these control loops adjusts the setpoint automatically?
Reset system
150
The power to operate a control system may come from
fluid under pressure
151
An RTD responds to a change in temperature by undergoing a change in its
electrical resistance
152
Relative humidity is defined as the amount of moisture in the air
divided by the amount it can hold
153
In a pressure sensor that uses a Bourdon tube, changes in pressure are sensed by changes in the ___ of the tube.
position of the sealed end
154
An air-conditioning system has a two-position damper in the duct bringing outside air into the building and a second two-position damper in the return-air duct. When the system shuts down, the outside-air damper should be ___ and the return-air damper should be ___.
closed; open
155
Which of the following is an advantage of variable-speed drives over older methods of controlling output of an air-conditioning or refrigeration system?
Proportional control can be used
156
Unlike floating control, proportional control is
continuous
157
The air supply for a pneumatic control system requires which of the following
Drier
158
A PE relay is used to control a device operated by
electricity
159
Setting the gain of a controller determines how much a change in the ___ affects the ___.
controlled variable; controlled device
160
Adding integral action to a controller improves system performance by reducing ___. Adding derivative action improves performance by reducing ___.
offset; overshoot and undershoot
161
In pumpdown control, the compressor starts when the pressure ___ in the ___.
increases; suction line
162
The high-pressure control in the discharge line of an air-conditioning or refrigeration system responds to high pressure by
shutting down the compressor
163
A differential-pressure oil-safety control shuts off the compressor if the difference in pressure between the ___ and the oil pump ___ does not become high enough within a given time.
compressor crankcase; discharge
164
What kind of capacity control is commonly used on large reciprocating compressors?
Cylinder unloading
165
In modulating the flow of water to hydronic terminals, the temperature control method has the advantage of
preventing system freeze-up in cold weather
166
In setting up a preventive maintenance (PM) program, your first step should be to
inspect the system in detail
167
To maintain oil pressure in a 10-hp reciprocating compressor, a ___ oil pump is used.
positive-displacement
168
To adjust the water-regulating valve on a water-cooled condenser, you should turn the adjusting screw until the ___ is at the design value. You should make this adjustment when the equipment is running at ___ load.
head pressure; maximum
169
The main requirements for maintaining a pneumatic control system include
removing and disassembling valves
170
The main requirements for maintaining an electric or electronic control system include
checking electrical contacts for pitting
171
The function of an evaporator is to ___ heat from the ___.
remove; material being cooled
172
The capacity of an evaporator is affected by the
cleanliness of the evaporator
173
Basic evaporator configurations depend on whether they have one or more tubes and whether or not they travel
extended surface areas
174
Multiple-circuit evaporators have headers or distributors that direct refrigerant to each coil from ___ expansion valve
one
175
A comfort cooler ___ the humidity of moist air by cooling the air to a temperature ___ the dew point.
reduces; below
176
Unlike a dry-expansion evaporator, refrigerant in a flooded evaporator enters as ___ liquid and exits as ___ vapor.
all; part
177
In a ___ refrigeration system, the refrigerant removes heat from the material to be cooled. This refrigerant then transfers heat to the ___ refrigerant.
secondary; primary
178
A eutectic solution is a brine in which the concentration of salt is precisely set to achieve the lowest possible
freezing point
179
Which evaporator arrangement offers the greatest flexibility?
Two evaporators in parallel, each with its own expansion valve
180
A cascade refrigeration system has more than one
compressor, evaporator, condenser, and refrigerant
181
The basic law of thermodynamics that apply to refrigeration state that
heat flows from a warmer substance to a cooler substance
182
The net refrigeration effect can be increased by ___ the refrigerant.
sub-cooling
183
Using a heat exchanger to lower the temperature in the liquid line and raise the temperature in the suction line has the advantage of reducing
the amount of liquid refrigerant entering the compressor
184
The amount of oil entering tan evaporator can be reduced by using an
oil separator
185
If the fluid being cooled by an evaporator circulates through the coil rather than moving slowly or not at all, the performance of the evaporator improves because of the
increased temperature difference across the wall of the evaporator
186
An evaporator can be defrosted by
reversing the flow of refrigerant
187
To remove rust, scale, and sludge from a shell-and-tube evaporator, you should use a ___, as necessary.
brush
188
A water coil can be winterized by draining out the water and
leaving the coil dry for the winter
189
Frost buildup on an evaporator coil is increased by ___ airflow and ___ air.
low; humid
190
Bent fins reduce the cooling capacity of an evaporator, because they
reduce the area exposed to the air
191
The purpose of the metering device in a refrigeration system is to
control the flow of refrigerant into the evaporator
192
The operation of an AXV is controlled by the
pressure in the evaporator
193
In controlling the flow of refrigerant into a flooded evaporator, the float of a high-side valve is located on the
high-pressure side of the valve port
194
If floodback occurs in a system using an AXV, a likely cause is
ice in the spring chamber above the diaphragm
195
A common problem with TXVs is ice in the valve port. The proper way to correct this problem is to
replace the filter-drier
