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Mech 7th 6th Month Final > Study > Flashcards

Study Flashcards

1
Q

I 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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2
Q

At a temperature of -30°F, the enthalpy of the saturated liquid refrigerant (hr ) is 3.5 Btu/b. The
enthlapy of evaporation (hip ) is 87 4 Btu/b What is the enthalpy of the saturated vapor (hg )?

A

90.9 Btu,lb

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3
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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4
Q

Choose values from the list below when making your calculations:
Condensing pressure = 232 psia
Evaporating pressure = 61 psia
Refrigerating effect = 62 Btu/lb
Enthalpy of condenser pressure = 115 Btu/lb
Enthalpy at evaporator pressure = 98 Btu/lb
One ton of refrigeration - 200 Btu/min
One horsepower = 33 000 ft 1b/min -
- 42 4 Blu/min

A

10.3Hp

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5
Q

Liqund tefugerant can be subcooled by transferring hot euther to the atmosphere in the condenser or to the____
It tho suction line heat exchanger

A

Refrigerant vapor

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6
Q

In the ASHRAE standard designations of refrigerant, the

A

Letter R is being replaced by letters identifying the chemical structure

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7
Q

Temperature glide occurs only in____
refrigerants

A

Blended

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8
Q

ASHRAE classifies refrigerants according to how hazardous they are. The most hazardous refrigerants are rated____

A

B3

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9
Q

When handling out and storing refrigerants , you must protect yourself by

A

avoiding any open flame

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10
Q

The ozone layer in the earths atmosphere is important, because it

A

Absorbs ultraviolet radiation from the sun

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11
Q

CFCs contribule to the greenhouse effect by

A

absorbing infrared radiation

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12
Q

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

A

recyele refrigerants on-site, if possible

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13
Q

A recycled refrigerant may be placed in

A

The system from which it was removed

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14
Q

During The installation of a new system lhe chance of future refrigerant leaks can be reduced by

A

installing a muffler in the compressor discharge line

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15
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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16
Q

The EPA’s 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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17
Q

The compressor for an active recovery system is part of the_____ The compressor for a passive recovery systern is part of the____

A

recovery equipment; systern being serviced

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18
Q

Technicians who work on residential air conditioning systems must have at least_____certification

A

Type ll

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19
Q

Which of the following documents is required by the FPA?

A

Certification activity report

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20
Q

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

A

Acid

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21
Q

An absorption type desiccant holds water by means ol a(n)_____ action, but an adsorption-type desiocant holds water by means of a(n)____action.

A

Chemical; mechanical

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22
Q

If you mount a filter-drier in a vertical suction line the mlet should be located at the top so that____cannot become lapped inside.

A

Oil

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23
Q

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

A

minimum particle size it can trap

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24
Q

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

A

wear safety goggles

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25
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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26
Q

When preparing to us 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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27
Q

To check the charge in a refrigeration system vou can look al the______ in the liquid lines. If the change is low you will probebly see

A

sight glass; bubbles

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28
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 to about pressure lells you the system is

A

1,000; not dry

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29
Q

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

A

weight of the refrigerant used

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30
Q

The miscibility of a refrigerant oil is its abilty to

A

mix with the refrigerant

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31
Q

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

A

Clogged desiccant

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32
Q

 An oil separator is located between the_____the______ in order to keep oil out of the condenser and evaporalor

A

compressor: condenser

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33
Q

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

A

blockage in cold parts of the system

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34
Q

Belore you check the oil level in the sight- glass on a relrigeration comprossor, 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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35
Q

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

A

Centrifugal

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36
Q

Which of the following is part of a scroll compressor?

A

Swing link

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37
Q

A multiple stage refrigeration system has more than one

A

Compressor

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38
Q

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

A

Discharge pressure

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39
Q

Among reciprocating compressors, the crankshaft is usually vertical in a(n)_____
compressor, but horzontal in a(n)_____
compressor

A

full-hermetic, open

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40
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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41
Q

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

A

Crankshaft splash

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42
Q

A cylinder unloader reduces the capacity of a reciprocating compressor by allowing refrigerant to Now through the_____
port during the____stroke.

A

suction; compression

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43
Q

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

A

spring mounts

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44
Q

One advantage of rotary compressors over reciprocating compressors is that the

A

Vibration is less

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45
Q

Slugging is the entry of______
collapse of______refrigerant into a compressor Cavitation is the formation and in a liquid flowing under pressure.

A

liquid; vapor pockets

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46
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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47
Q

Helical compressors differ from rotary compressors in that they have

A

No vanes

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48
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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49
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 of; diameter

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50
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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51
Q

In multistage centrifugal compressors, thrust loads are reduced by

A

Opposing impellers

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52
Q

The purpose of a purge system on a condenser is to eliminate_____ from the refrigeration system.

A

Air

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53
Q

Reducing a compressor’s capacity by closing pre-rotation vanes raises the pressure in the system’s_____

A

Evaporator

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54
Q

Which of the following is an important factor to consider when selecting a motor to run a refrigeration compressor?

A

Horsepower rating

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55
Q

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

A

Capacitor-start, induction-run

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56
Q

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

A

reversing the connection of either the starting or running winding

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57
Q

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

A

connect the two running windings in series

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58
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 operateswhen the voltage across the_____winding rises to a preset value

A

running; starting

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59
Q

The two basic categories of motor starting devices are

A

contactors and starters

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60
Q

A reduced vollage starter lirits the current to the motor at startup in order to prevent

A

voltage drops to other equipment

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61
Q

Overload protection for compressor motors may be provided by a(n)

A

external bimetallic disk

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62
Q

Crankcase heaters are especially useful on compressors that are subjected to

A

Cold climates

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63
Q

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

A

Slugging

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64
Q

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

A

follow the manufacturer’s recommended maintenance schedules and
procedures

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65
Q

Typical preventative maintenance procedures for compressors and related equipment include

A

listening for unusual noises

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66
Q

A compressor may overheat because of a(n)

A

Low oil level

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67
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_____DSIg

A

+2 to +5

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68
Q

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

A

excessive wear on bearing surfaces

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69
Q

The function of an evaporator is to_____
heat (from/to) the______

A

remove; material being cooled

70
Q

The capacity of an evaporator is affected by the

A

cleanliness of the evaporator

71
Q

A comfort cooler______the humidity of moist air by cooling the air to a temperature______the dew point.

A

reduces; below

72
Q

Unlike a dry-expansion evaporator, refrigerant in a flooded evaporator enters as_____liquid and exits as______ vapor

A

All;part

73
Q

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

A

Freezing point

74
Q

Which evaporator arrangement offers the greatest flexibility?

A

Two evaporators in parallel, each with its own expansion valve

75
Q

A cascade refrigeration system has more lhan one

A

compressor, evaporator, condenser, and refrigerant

76
Q

The basic law(s) of thermodynamics that apply to refrigeration state that

A

heat flows from a warmer substance to a cooler substance

77
Q

The net refrigeration effect can be increased by_____the refngerant.

A

Subcooling

78
Q

Using a heat exchanger to lower the temperature in the liquid line and raise the temperature in the suction line has the advantage(s) of reducing

A

the amount of liquid refrigerant entering the compressor

79
Q

The amount of oil entering an evaporator can be reduced by using a(n)

A

Oil separator

80
Q

If the fluid being cooled by an evaporator circulates through the coil rather that moving slowly or not at all, the perfornance of the evaporator improves because of the

A

increased temperature difference across the wall of the evaporator

81
Q

An evaporator can be defrosted by

A

reversing the flow of refrigerant

82
Q

To remove rust, scale, and sludge from a shell-and tube evaporator you should use a(n)_____as necessary.

A

Brush

83
Q

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

A

leaving the coil dry for the winter

84
Q

Frost buildup on an evaporator coil is increased by_____airflow and____ air

A

Low;humid

85
Q

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

A

reduce the area exposed to the air

86
Q

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

A

control the flow of refrigerant into the evaporator

87
Q

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

A

high-pressure side of the valve port

88
Q

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

A

ice on the spring chamber above the diaphragm

89
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

90
Q

The operation of an AXV is controlled by the

A

pressure in the evaporator

91
Q

In a secondary-refrigeration system, the refrigerant removes heat from the material to be cooled. This refrigerant then transfers heal to the ______
refrigerant In the process, that____

A

Secondary; primary

92
Q

An ideal” refrigerent has which of the following charactenslics?

A

Nonflammable

93
Q

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

A

compress refrigerant vapor in a chamber

94
Q

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

A

extended surface areas

95
Q

Mulliple-circuit evaporators have headers or distributors that direct refrigerant to each coil from_____ expansion valve(s)

A

One

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

depend on air circulating over the coils

98
Q

Low-ambient control in 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(s):

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

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

A

Induced draft, counterflow

107
Q

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

A

Bleedoff valve

108
Q

The capacily of a cooling tower can be controlled by means of (a)

A

Diverting valve

109
Q

As part of maintaining a cooling tower, you should check the_______ everyday

A

Float valve for clogging

110
Q

Tho basic classifications for evaporative condensers are

A

blow through and draw-through

111
Q

An evaporative condenser may include a desuperheating coil for the purpose of

A

reducing the formation of scale

112
Q

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

A

circulating water intermittently

113
Q

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

A

Installing a sump heater

114
Q

As a part of maintaining an evaporative condenser you should check the________
every three months.

A

fan blades for tightness

115
Q

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

A

Corrosion

116
Q

Corrosion in a water-cooled system can be caused by

A

biological organisms

117
Q

Scale formation can be reduced in a refrigeration system by adding______ to the cooling water

A

Acid

118
Q

Bactera and algae can be controlled in a refrigeration system by adding_____ to the cooling water

A

Chlorine

119
Q

Chemical detenoration in a wooden cooling tower can be controlled by

A

keeping the pH of circulating water in the 6.0 to 7.5 range

120
Q

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

A

Increase in air velocity across the surface

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

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

A

convey the refrigerant to the condenser

126
Q

The “ontrainment” of compressor oil is the_____ The moving refrigerant

A

drawing in and transporting of oil with

127
Q

In order to keep entrained oil droplets moving through the piping, the refrigerant must move at______fpm in horizontal piping and______fom in a vertical riser.

A

500 to 700; 750 to 1,500

128
Q

Refrigerant can be prevented from pollecting in the compressor during the off cycle by installing a(n)______ in (on) the______

A

check valve: discharge line

129
Q

Accossones often added to a discharge line include a(n)

A

discharge muffler

130
Q

Subcooling is desirable in the liquid line, because it

A

reduces the volatility of the refrigerant

131
Q

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

A

refrigerating effect

132
Q

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

A

oil is miscible in most liquid refrigerants

133
Q

A liguid receiver is used lo

A

store all the refrigerant during repairs

134
Q

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

A

Evaporator

135
Q

A double suction riser installed in a cooling system enables the system lo operate at maximum load without creating excessive_______in the suction line

A

Pressure drop

136
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

137
Q

An evaporator pressure regulalor valve closes part way if the pressure at the evaporator outlet becomes too______ A crankcase-pressure regulator valve closes part way if pressure at the compressor inlet becomes too______

A

low; high

138
Q

The suction line is insulated in order to prevent or reduce______the line

A

condensation on the outside of

139
Q

The amount of od fat can build up in The suction line of an idlo single compressor system 15 much_______ than the amount hat cen build up m an idle comoressor of a multiple compressor system. To prevent damage from excessive oil buildup the suction lino should include a trap
win the minimum rise of______in

A

Less; 14

140
Q

Piping problems that result in operating problems are often caused by

A

Liquid hammer

141
Q

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

A

Bellows

142
Q

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

A

Rod-type hanger

143
Q

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

A

damage to the valves and controls

144
Q

Insulalion is needed on the liguid 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; subcooling

145
Q

When brazing tubing to a fitting, you should first heat the________ until the _______melts.

A

Fitting; flux

146
Q

What is he main function of a control system?

A

Maintain a variable at a setpoint

147
Q

Air conditioning and refrigeration systems are commonly controlled by_________control

A

Proportional

148
Q

The power to operate a control system may come from

A

Fluid under pressure

149
Q

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

A

Electrical resistance

150
Q

Relalive humidity is defined as the amount of moistore in the air

A

divided by the amount it can hold

151
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 sealed end

152
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

153
Q

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

A

Proportional control can be used

154
Q

Unlike floating control, the proportional control is

A

Continuous

155
Q

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

A

Drier

156
Q

A PE relay is used to control a device operated by______

A

Electricity

157
Q

Setting the gain of a controller determines how much a change in the______ affects the_________

A

controlled variable; controlled device

158
Q

Adding integral action to a controller improves system performance by reducing_______. Adding derivative action improves performance by reducing_________.

A

offset; overshoot and undershoot

159
Q

In pumpdown control, the compressor starts when the pressure________ in the_______

A

increases; suction lime

160
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

161
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

162
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

163
Q

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

A

inspect the system in detail

164
Q

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

A

positive-displacement

165
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

166
Q

The main requirements for maintaining a pneumatic control system include

A

removing and disassembling valves

167
Q

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

A

checking electrical contacts for pitting

168
Q

Which of these control loops adjusts the setpoint automatically?

A

Reset system

169
Q

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

A

Cylinder unloading

170
Q

What are the basic component of a control system ?

A

Sensor, controller, controlled device

Mech 7th 6th Month Final (1 decks)

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