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76 > 7th 6 Months Final > Flashcards

7th 6 Months Final Flashcards

1
Q

Refrigeration is the process of ___ the air in a defined space.

A

lowering the temperature of

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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

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3
Q

The two kinds of air conditioning are

A

comfort and process

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4
Q

One of the physical states of matter is

A

gas

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5
Q

You can cause matter to change its physical state by

A

adding or removing heat

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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

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7
Q

A temperature of 45 degrees F is about the same as ___ degrees C.

A

7

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8
Q

Heat can be transferred from one place to another by the process of

A

conduction

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9
Q

The latent heat of vaporization of a substance is the amount of heat the substance absorbs as it

A

evaporates

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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

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11
Q

From the compressor, refrigerant flows to the

A

condenser

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12
Q

The graph below is the pressure-temperature chart for a refrigerant. Point ___ represents a condition of superheating.

A

1

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13
Q

Compared to a dry-expansion evaporator, a flooded evaporator of the same size

A

is more efficient

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14
Q

The purpose of a cooling medium is to

A

remove heat from compressed refrigerant vapor

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15
Q

An automatic expansion valve is a metering device that maintains a constant pressure in the

A

evaporator

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16
Q

The properties of air that are important in psychrometrics include

A

enthalpy

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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

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18
Q

Air that is saturated is air that is at the

A

dewpoint temperature

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19
Q

Relative humidity changes if the ___ changes, but the specific humidity does not.

A

dry-bulb temperature

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20
Q

To calculate the enthalpy of a sample of air, you must include

A

latent heat of the water vapor

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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

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22
Q

One useful method of detecting leaks in a refrigeration system involves using an ____ leak detector.

A

electronic

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23
Q

Relative humidity can be measured with an

A

hygrometer

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24
Q

Which of the following is a correct match between an electrical value and the instrument used to measure it?

A

Resistance; ohmmeter

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25
Q

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.

A

Chemical; container of refrigerant

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26
Q

If you increase the pressure of a liquid, its ___ temperature will ____, meaning that it will boil at a higher temperature.

A

saturation; increase

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27
Q

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?

A

90.9 BTU/lb

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28
Q

In the following diagram of a refrigeration cycle, the line between points ___ represents the amount of subcooling

A

2 & 3

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29
Q

A system must provide 8 tons of refrigeration. What compressor horsepower is needed for this system?

A

10.3 HP

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30
Q

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.

A

refrigerant vapor

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31
Q

An “ideal refrigerant” has which of the following characteristics?

A

Non-flammable

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32
Q

In the ASHRAE standard designations of refrigerants, the

A

letter R is being replaced by letters identifying the chemical structure.

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33
Q

Temperature glide occurs only in ___ refrigerants.

A

blended

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34
Q

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

A

B3

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35
Q

When handling and storing refrigerants, you must protect yourself by

A

avoiding any open flame

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36
Q

The ozone layer in the earth’s atmosphere is important because it

A

absorbs ultraviolet radiation from the sun

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37
Q

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

A

absorbing infrared radiation

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38
Q

In order to minimize the release of CFCs into the atmosphere, refrigeration service technicians must

A

recycle refrigerants on-site, if possible

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39
Q

A recycled refrigerant may be placed in

A

the system from which it was removed

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40
Q

During the installation of a new system, the chance of future refrigerant leaks can be reduced by

A

installing a muffler in the compressor discharge line

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41
Q

To reduce the depletion of the ozone layer, the U.S. government has implemented laws requiring the

A

testing and certification of all technicians whose work can cause the release of harmful refrigerants

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42
Q

The EPAs final rule concerning the handling of refrigerants and refrigeration equipment requires

A

certifying the equipment used in recycling and reclaiming refrigerants

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43
Q

The compressor for an active recovery system is part of the ____. The compressor for a passive system is part of the ___.

A

recovery equipment; system being serviced

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44
Q

Which of the following is required by the EPA

A

Certification activity report

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45
Q

Technicians who work on residential air conditioning systems must have at least _____ certification.

A

Type II

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46
Q

Which of the following is a contaminant that can be removed by a filter-drier?

A

Acid

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47
Q

An absorption type desiccant holds water by means of a ___ action, but an adsorption type desiccant holds water by means of a ___ action.

A

chemical; mechanical

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48
Q

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.

A

oil

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49
Q

When selecting a filter-drier, you need to base your selection in part on the

A

minimum particle size it can trap

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50
Q

When installing a filter-drier in a refrigeration system, you should

A

wear safety goggles

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51
Q

You can pinpoint leaks in a new refrigeration system by charging the system with ___ and using a ___

A

nitrogen; soap solution

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52
Q

When preparing to use a gauge manifold in servicing a pressurized refrigeration system, you connect its high-side charging hose to the

A

compressor discharge service valve

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53
Q

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 ___.

A

sight glass; bubbles

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54
Q

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 ___.

A

1,000; not dry

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55
Q

You can tell whether you have charged a refrigeration system with the correct amount of refrigerant by checking the

A

weight of refrigerant used

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56
Q

The miscibility of the refrigerant oil is its ability to

A

mix with the refrigerant

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57
Q

Oil that becomes mixed with the refrigerant in a system can cause which of the following problems?

A

Clogged desiccant

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58
Q

An oil separator is located between the ____ an ___ in order to keep oil out of the condenser and evaporator.

A

compressor; condenser

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59
Q

Moisture in a refrigeration system causes a variety of problems, including

A

blockage in cold parts of the system

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60
Q

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.

A

ten minutes; stopped

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61
Q

A positive-displacement compressor uses a piston or other device to

A

compress refrigerant vapor in a chamber

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62
Q

Which of the following is a kind of kinetic displacement compressor?

A

centrifugal

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63
Q

Which of the following is part of a scroll compressor?

A

Swing link

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64
Q

A multiple stage refrigerant system has more than one

A

compressor

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65
Q

When selecting a replacement compressor, you need to make the replacement will operate (with/at) the proper

A

discharge pressure

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66
Q

Among reciprocating compressors, the crankshaft is usually vertical in a ___ compressor, but horizontal in an ____ compressor

A

full-hermetic; open

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67
Q

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.

A

bottom; top

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68
Q

Which of the following is a method of distributing lubricating oil in a reciprocating compressor?

A

Crankshaft splash

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69
Q

A cylinder unloader reduces the capacity of a reciprocating compressor by allowing refrigerant to flow through the ___ port during the ___ stroke.

A

suction; compression

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70
Q

One way of reducing vibration problems in reciprocating compressors involves the use of

A

spring mounts

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71
Q

One advantage of rotary compressors over reciprocating compressors is that the

A

vibration is less

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72
Q

Slugging is the entry of ___ refrigerant into a compressor. Cavitation is the formation and collapse of ____ in a liquid flowing under pressure.

A

liquid; vapor pockets

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73
Q

One purpose of the accumulator on a rotary compressor is to

A

keep dirt and debris out of the compressor

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74
Q

Helical compressors differ from rotary compressors in that they have

A

no vanes

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75
Q

In a scroll compressor, one scroll is stationary and the other ____. Refrigerant enters the scrolls at the ___ and leaves at the center.

A

orbits; outer edge

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76
Q

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

A

tip speed; diameter

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77
Q

In reverse hydrostatic sealing, the flow of ___ across the seal opposes the flow of ____ across the bearing.

A

refrigerant vapor; oil

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78
Q

18

A

18

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79
Q

19

A

19

80
Q

20

A

20

81
Q

21

A

21

82
Q

Which of the following motors can be used in hermetic compressors?

A

Capacitor start, induction-run

83
Q

You can reverse the direction of a single-phase induction motor by

A

reversing the connection of either the starting or the running winding

84
Q

To change a dual-voltage motor to run on 240 V instead of 120 V, you need to

A

connect the two running windings in series

85
Q

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.

A

running; starting

86
Q

Two basic categories of motor starting devices are

A

contactors and starters

87
Q

A reduced-voltage starter limits the current to the motor at startup in order to prevent

A

voltage drops to other equipment

88
Q

Overload protection for compressor motors may be provided by an

A

external bimetallic disk

89
Q

Crankcase heaters are especially useful on compressors that are subjected to

A

cold climates

90
Q

Installing a suction-line accumulator can protect a compressor from damage caused by

A

slugging

91
Q

The “first rule” of preventive maintenance for compressors and related components is to

A

follow the manufacturer’s recommended maintenance schedules and procedures

92
Q

Typical preventive maintenance procedures for compressors and related equipment include

A

listening for unusual noises

93
Q

A compressor may overheat because of a

A

low oil level

94
Q

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.

A

+2 to +5

95
Q

After disassembling a reciprocating compressor and cleaning the parts, you should inspect the parts for

A

excessive wear on the bearing surfaces

96
Q

The capacity of a condenser is affected by the

A

area of contact with the cooling medium

97
Q

Natural-draft air cooled condensers and forced air condensers are alike in that both types

A

need 600 to 1200 cfm of air per ton of capacity

98
Q

Low-ambient control in an air cooled condenser can be achieved by

A

closing the dampers

99
Q

Spring loaded relief valves protect a system against explosion by acting in response to high ___. Fusible plugs act in response to high ___.

A

pressure; temperature

100
Q

Periodic maintenance of air cooled condensers includes doing which of the following every three months?

A

checking all belts and pulleys

101
Q

In the ___ system, water passes through the condenser to cool the refrigerant. The water is then ___.

A

wastewater; discharged to the sewer

102
Q

In a water cooled condenser system, “makeup water” is used for

A

replacing water lost through evaporation

103
Q

Tube-in-tube, shell-and-coil, and shell-and-tube condensers are alike in the following way

A

liquid refrigerant collects at the bottom

104
Q

A condenser has a pressure-relief device that ___ if the refrigerant pressure becomes too high.

A

releases refrigerant

105
Q

Generally, how long should you allow a chemical cleaner to stand in a condenser

A

a few hours

106
Q

Which of the following can increase the capacity of a cooling tower or a spray pond by the greatest amount?

A

decrease in dry-bulb temperature of the air

107
Q

What type of cooling tower is shown in the drawing below?

A

induced draft, counter flow

108
Q

Which components in the water-circulating system for a cooling tower or spray pond are used to keep the concentration of minerals low?

A

bleed-off valve

109
Q

The capacity of a cooling tower can be controlled by means of a

A

diverting valve

110
Q

As part of maintaining a cooling tower, you should check the ___ everyday.

A

float valve for clogging

111
Q

The basic classifications of evaporative condensers are

A

blow through and draw through

112
Q

An evaporative condenser may include a de-superheating coil for the purpose of

A

reducing the formation of scale

113
Q

Which of the following methods will maintain condensing pressure during cold weather operation?

A

circulating water intermittently

114
Q

What will prevent the water in an evaporative condenser from freezing during cold weather?

A

installing a sump heater

115
Q

As part of maintaining an evaporative condenser, you should check the ___ every three months.

A

pulleys and belts for wear

116
Q

One of the main categories of water related problems in an air conditioning or refrigeration system is

A

corrosion

117
Q

Corrosion in a water cooled system can be caused by

A

biological organisms

118
Q

Scale formation can be reduced in a refrigeration system by adding ___ to the cooling water.

A

acid

119
Q

Bacteria and algae can be controlled in a refrigeration system by adding ___ to the cooling water.

A

chlorine

120
Q

Chemical deterioration in a wooden cooling tower can be controlled by

A

keeping pH of circulating water in the 6.0 to 7.5 range

121
Q

In a cooling system, one of the main lines in the piping system is the ___ line.

A

liquid

122
Q

Steel pipe is typically joined by means of

A

flanges

123
Q

Tubing is often preferred over piping in a cooling system because it

A

absorbs vibration better

124
Q

Refrigeration tubing is typically joined by

A

soldering

125
Q

When brazing tubing to a fitting, you should first heat the ___ until the ___ melts.

A

tubing; flux

126
Q

The function of the discharge line in a refrigeration system is to

A

convey the refrigerant to the condenser

127
Q

The “entrainment” of compressor oil is the ___ the moving refrigerant

A

drawing and transporting of oil with

128
Q

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.

A

500 to 700; 750; to 1,500

129
Q

Refrigerant can be prevented from collecting in the compressor during the off-cycle by installing a ____ in the ___.

A

check valve; discharge line

130
Q

Accessories often added to a discharge line include a

A

discharge muffler

131
Q

Sub-cooling is desirable in the liquid line, because it

A

reduces the volatility of the refrigerant

132
Q

If the pressure in the liquid drops, flash gas can form, which can reduce the

A

refrigerating effect

133
Q

With halocarbon refrigerants, the movement of oil is better in the liquid line than in the discharge line, because the

A

oil is miscible in most liquid refrigerants

134
Q

A liquid receiver is used to

A

store all the refrigerant during repairs

135
Q

The purpose of a solenoid valve in the liquid line is to stop the flow of refrigeration to the

A

evaporator

136
Q

A double suction riser installed in a cooling system enables the system to operate at maximum load without creating excessive ___ in the suction line.

A

pressure drop

137
Q

An accumulator in the suction line traps oil and liquid refrigerant to keep it from entering the ___. A heater in the accumulator evaporates the ___.

A

compressor; refrigerant

138
Q

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 ___.

A

low; high

139
Q

The suction line is insulated in order to prevent or reduce ___ the line.

A

condensation on the outside of

140
Q

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.

A

less; 14

141
Q

Piping problems that result in operating problems are often caused by

A

liquid hammer

142
Q

Which of the following expansion joints can be used in a refrigerant line?

A

Bellows

143
Q

Which kind of support is appropriate for a horizontal piping run 15 feet long?

A

Rod-type hanger

144
Q

The problems caused by vibration in the piping of a cooling system include

A

damage to valves and controls

145
Q

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.

A

much colder; sub-cooling

146
Q

What is the main function of a control system?

A

maintain a variable at a setpoint

147
Q

What are the basic components of a control system?

A

Sensor, controller, controlled device

148
Q

Air-conditioning and refrigeration systems are commonly controlled by ___ control.

A

proportional

149
Q

Which of these control loops adjusts the setpoint automatically?

A

Reset system

150
Q

The power to operate a control system may come from

A

fluid under pressure

151
Q

An RTD responds to a change in temperature by undergoing a change in its

A

electrical resistance

152
Q

Relative humidity is defined as the amount of moisture in the air

A

divided by the amount it can hold

153
Q

In a pressure sensor that uses a Bourdon tube, changes in pressure are sensed by changes in the ___ of the tube.

A

position of the sealed end

154
Q

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 ___.

A

closed; open

155
Q

Which of the following is an advantage of variable-speed drives over older methods of controlling output of an air-conditioning or refrigeration system?

A

Proportional control can be used

156
Q

Unlike floating control, proportional control is

A

continuous

157
Q

The air supply for a pneumatic control system requires which of the following

A

Drier

158
Q

A PE relay is used to control a device operated by

A

electricity

159
Q

Setting the gain of a controller determines how much a change in the ___ affects the ___.

A

controlled variable; controlled device

160
Q

Adding integral action to a controller improves system performance by reducing ___. Adding derivative action improves performance by reducing ___.

A

offset; overshoot and undershoot

161
Q

In pumpdown control, the compressor starts when the pressure ___ in the ___.

A

increases; suction line

162
Q

The high-pressure control in the discharge line of an air-conditioning or refrigeration system responds to high pressure by

A

shutting down the compressor

163
Q

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.

A

compressor crankcase; discharge

164
Q

What kind of capacity control is commonly used on large reciprocating compressors?

A

Cylinder unloading

165
Q

In modulating the flow of water to hydronic terminals, the temperature control method has the advantage of

A

preventing system freeze-up in cold weather

166
Q

In setting up a preventive maintenance (PM) program, your first step should be to

A

inspect the system in detail

167
Q

To maintain oil pressure in a 10-hp reciprocating compressor, a ___ oil pump is used.

A

positive-displacement

168
Q

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.

A

head pressure; maximum

169
Q

The main requirements for maintaining a pneumatic control system include

A

removing and disassembling valves

170
Q

The main requirements for maintaining an electric or electronic control system include

A

checking electrical contacts for pitting

171
Q

The function of an evaporator is to ___ heat from the ___.

A

remove; material being cooled

172
Q

The capacity of an evaporator is affected by the

A

cleanliness of the evaporator

173
Q

Basic evaporator configurations depend on whether they have one or more tubes and whether or not they travel

A

extended surface areas

174
Q

Multiple-circuit evaporators have headers or distributors that direct refrigerant to each coil from ___ expansion valve

A

one

175
Q

A comfort cooler ___ the humidity of moist air by cooling the air to a temperature ___ the dew point.

A

reduces; below

176
Q

Unlike a dry-expansion evaporator, refrigerant in a flooded evaporator enters as ___ liquid and exits as ___ vapor.

A

all; part

177
Q

In a ___ refrigeration system, the refrigerant removes heat from the material to be cooled. This refrigerant then transfers heat to the ___ refrigerant.

A

secondary; primary

178
Q

A eutectic solution is a brine in which the concentration of salt is precisely set to achieve the lowest possible

A

freezing point

179
Q

Which evaporator arrangement offers the greatest flexibility?

A

Two evaporators in parallel, each with its own expansion valve

180
Q

A cascade refrigeration system has more than one

A

compressor, evaporator, condenser, and refrigerant

181
Q

The basic law of thermodynamics that apply to refrigeration state that

A

heat flows from a warmer substance to a cooler substance

182
Q

The net refrigeration effect can be increased by ___ the refrigerant.

A

sub-cooling

183
Q

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

A

the amount of liquid refrigerant entering the compressor

184
Q

The amount of oil entering tan evaporator can be reduced by using an

A

oil separator

185
Q

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

A

increased temperature difference across the wall of the evaporator

186
Q

An evaporator can be defrosted by

A

reversing the flow of refrigerant

187
Q

To remove rust, scale, and sludge from a shell-and-tube evaporator, you should use a ___, as necessary.

A

brush

188
Q

A water coil can be winterized by draining out the water and

A

leaving the coil dry for the winter

189
Q

Frost buildup on an evaporator coil is increased by ___ airflow and ___ air.

A

low; humid

190
Q

Bent fins reduce the cooling capacity of an evaporator, because they

A

reduce the area exposed to the air

191
Q

The purpose of the metering device in a refrigeration system is to

A

control the flow of refrigerant into the evaporator

192
Q

The operation of an AXV is controlled by the

A

pressure in the evaporator

193
Q

In controlling the flow of refrigerant into a flooded evaporator, the float of a high-side valve is located on the

A

high-pressure side of the valve port

194
Q

If floodback occurs in a system using an AXV, a likely cause is

A

ice in the spring chamber above the diaphragm

195
Q

A common problem with TXVs is ice in the valve port. The proper way to correct this problem is to

A

replace the filter-drier

76 (1 decks)

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