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ua hvac star exam prep > Commercial Refrigeration Service Technician Study Guide - 2007 > Flashcards

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

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2
Q

All refrigerants have flammability and the toxicity classifications. Where
could a technician best find those ratings?

A

Compressor

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3
Q

The main function of an expansion device is to?

A

Meter the refrigerant

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4
Q

The main function of an expansion device is to?

A

Store excess refrigerant

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5
Q

How does a technician determine whether or not there is liquid refrigerant
leaving the evaporator?

A

calculates what the evaporator superheat

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6
Q

Which of the following is NOT TRUE about refrigerant as it enters the
condenser?

A

it is subcooled

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7
Q

Any additional heat added to the refrigerant after its 100% saturated vapor
condition is called?

A

Superheat

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8
Q

Most of the heat absorbed in the low side of a refrigeration system is.

A

latent heat

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9
Q

If a technician subtracted liquid line temperature from high side
condensing temperature he would

A

Subcooling

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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

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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

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12
Q

A refrigerant that is not miscible with mineral oil is

A

R-404A

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13
Q

Which lubricant is most commonly used with HFC-134a refrigerant?

A

polyolester

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14
Q

Polyol Ester oils are?

A

hygroscopic

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15
Q

Refrigerant tanks must always be stored in an area where the temperature
will not exceed

A

125º F

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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

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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

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18
Q

Which of the following gasses is non flammable and would be preferred
when leak testing a system?

A

CO2 & Nitrogen

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19
Q

Refrigerant cylinders that are labeled “Disposable”

A

by law cannot be refilled & are color-coded for easy identification

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20
Q

A refrigerant cylinder that has been DOT approved for refilling must

A

never be filled over 80% capacity

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21
Q

When calculating how much refrigerant can be placed into a rechargeable
cylinder,

A

tare lbs

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22
Q

All refrigerants have flammability and the toxicity classifications. Where
could a technician best find those ratings?

A

the MSDS

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23
Q

Double suction riser are used in refrigeration system when

A

large fluctuations in system capacity will occur

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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

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25
Q

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?

A

capillary action

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26
Q

Before proceeding to make any braze connection in a refrigeration system
all of the internal piping should be purged of atmosphere with

A

CO2 & Nitrogen

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27
Q

The liquid receiver is located between the?

A

condenser and the expansion device

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28
Q

Which device is used in a refrigeration system to protect the compressor
from liquid slugs?

A

suction accumulator

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29
Q

Which device is used to stop the flow of liquid or vapor in a refrigeration
system?

A

solenoid valve

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30
Q

Why is it important to know the direction that a scroll compressor is
rotating?

A

it will only pump refrigeration in one direction of rotation

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31
Q

An electric motor that has a voltage rating of 120 volts will have an upper
and lower allowable voltage limit of

A

108 to 132 V

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32
Q

On a fully welded hermetic compressor the electrical start components are
located

A

on the external of the compressor at the terminal box

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33
Q

On most hermetically sealed compressors

A

he motor and pumping mechanism are cooled by refrigerant

vapor

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34
Q

The difference between oil pump discharge pressure and crankcase
pressure on

A

net oil pressure

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35
Q

The amount of space between the piston at top-dead-center and the
bottom

A

clearance volume

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36
Q

The flapper valve design is less efficient than the discus valve design
because

A

the cylinder has more clearance volume than the discus

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37
Q

Liquid refrigerant entering the compressor is potentially more damaging
for this type of compressor over the others listed

A

reciprocating

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38
Q

Discus, ring, and flapper valves are not used on

A

Screw and Scroll Compressors

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39
Q

The main function of a condenser in a refrigeration system is?

A

reject the heat that is absorbed in the evaporator

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40
Q

The shell and tube condenser is a type of

A

water cooled condenser

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41
Q

One of the main disadvantages of a water-cooled condenser is that
mineral deposits

A

insulator

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42
Q

A flow regulating valve could be used on this type of condenser

A

shell and tube

Tube in Tube

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43
Q

On a water cooled condenser the water leaving the condenser is normally
______ lower than the condensing temperature of the unit

A

10º F

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44
Q

On a standard efficiency air-cooled condenser the ambient air entering the
condenser will be approximately ________ lower than the condensing

A

30º F

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45
Q

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

A

unit located in a colder climate operating all year

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46
Q

What type of expansion valve regulates its flow based from suction line
superheat?

A

TXV

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47
Q

Systems where the pressure drop across the evaporator is excessive
would typically use a/an.

A

externally equalized TXV

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48
Q

On a system equipped with a TXV, when the load on an evaporator
decreases.

A

the TXV decreases the flow of refrigerant

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49
Q

When referring to a power head on an expansion device the bulb is

A

normally charged with a fluid similar to that of the system refrigerant

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50
Q

By subtracting the low side evaporator outlet temperature from the low
side

A

evaporator superheat

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51
Q

On a typically evaporator employing a TXV the liquid refrigerant should be
completely boiled to a vapor?

A

near the evaporator outlet

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52
Q

What type of TXV would be best for an application that was exposed to
fluctuating ambient temperatures?

A

balanced port TXVs

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53
Q

Pressure-limiting TXV’s are generally applied on systems when

A

it is necessary to shut off the refrigerant flow to the evaporator when the suction pressure reaches a predetermined pressure.

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54
Q

Which of the following is not true regarding the evaporator in a
refrigeration system?

A

it rejects heat from the conditioned space

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55
Q

Heat that is added to the refrigerant stream after the 100% saturated
vapor point is called?

A

superheat

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56
Q

Multiple refrigerant circuits are preferred on evaporators that are?

A

Large or long

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57
Q

In a system where the evaporator temperature operators above 32º F the
technician needs to be concerned with?

A

The system would not need a method of defrost since the coil would not collect frost

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58
Q

The fin spacing per inch on a medium-temperature evaporator is

A

closer together than on low-temperature evaporator

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59
Q

A refrigeration system that utilizes two or three stages of low temperature
refrigeration

A

is called a cascade refrigeration system

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60
Q

When leak testing a refrigeration system using a high pressure nitrogen
tank the technician should always

A

use a pressure regulator and safety relief value at the nitrogen
tank

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61
Q

The maximum pressure that can be applied to a refrigeration system when
pressure testing is

A

determined by the systems rated nameplate test pressures

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62
Q

The safest way to charge refrigerant into a system that is running is with

A

vapor into the low side

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63
Q

When heating a refrigerant cylinder the technician should never use

A

any type of open flame

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64
Q

Refrigeration systems must be fully evacuated before charging with
refrigerant

A

to remove air and moisture from the system

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65
Q

A vacuum pump will lose its ability to draw a deep vacuum over time
because

A

the oil becomes full of moisture and acids which will decrease the capability of the vacuum pump

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66
Q

A refrigerant service valve must be placed in the

A

mid position in order for the technician to access the system

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67
Q

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

A

500 microns

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68
Q

Amperage is a measure of

A

electron flow

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69
Q

Voltage is the measure of

A

electrical pressure

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70
Q

Wattage is a measure of

A

electrical power

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71
Q

746 watts equals

A

1 horsepower

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72
Q

One kilowatt is equal to

A

3412 Btus

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73
Q

The unit of measurement for magnetic flux is?

A

maxwell

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74
Q

On a resistive electrical circuit which law would be used to calculate I, E or
R?

A

Ohm’s

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75
Q

Which of the following formula would be used to calculate amperage in
resistive circuit?

A

I=RE

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76
Q

Capacitance represents a components ability to

A

store electrons

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77
Q

A meter with the capacity to measure very high resistances is call a?

A

megger

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78
Q

A technician would use a micron gauge to measure?

A

deep vacuum

79
Q

If a technician has set his VOM meter to R x 100 he would be measuring

A

resistance

80
Q

When checking resistance through a motor winding the proper instruments
to use would be a/an?

A

ohmmeter

81
Q

An ohmmeter will measure infinite resistance when testing an

A

Open Fuse & Open contacts

82
Q

If a technician has placed his VOM in parallel with an energized load he is
probably checking?

A

voltage

83
Q

When a technician is checking unknown _______ he should always set
the instrument to the highest scale to prevent damage to the meter.

A

Voltage & Amperage

84
Q

If a technician has placed his VOM in series with the load he is probably
checking?

A

Amperage

85
Q

Which of the following instruments would be used to check the condition of
insulation on a motors windings?

A

megohmmeter

86
Q

A ladder diagram can also be called

A

electrical line wiring diagram

87
Q

A pictorial diagram will?

A

show approximate location of electrical system components

88
Q

The primary and secondary windings in a transformer are wired in?

A

not connected electrically

89
Q

What happens when the length of the path of an electrical circuit is
decreased?

A

there will be a decrease in total circuit resistance

90
Q

What is the total amperage of a circuit when two 25 ohm resistors are
connected in series using a 120 volt power source?

A

2.4 amps

91
Q

If the voltage is the same across each load in a circuit it would be
considered?

A

parallel circuit

92
Q

If a circuit is designed to allow the flow of electrons to follow only one path
it would be?

A

rectifier circuit

93
Q

A line or ladder type diagram is most useful for?

A

understanding circuit operation

94
Q

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?

A

0 volts

95
Q

An ohmmeter must never be connected to a

A

energized circuit

96
Q

If a 24 volt control transformer has a VA rating of 60 what is the maximum
amperage rating?

A

2.5 amp

97
Q

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?

A

T1 is Run
T2 is Common
T3 is Start

98
Q

The contacts of a current relay

A

are normally open contacts

99
Q

A motor starter is also called a?

A

motor controller

100
Q

If a relay coil is open the technician would read ______ when checking if
with his ohmmeter

A

Infinite resistance & zero resistance

101
Q

A sensor that uses a positive temperature coefficient thermistor (PTCT)

A

increases resistance as temperature increases

102
Q

These devices are used to protect electrical circuits from overcurrent

A

fuses and breakers

103
Q

If two 30 µf run capacitors are wired in parallel what is the new microfarad
rating on the circuit?

A

60 µf

104
Q

On a hermetic compressor what component is designed into the

compressor to protect against excessive temperatures and overcurrent

A

an overload protector

105
Q

The contacts of a potential relay

A

are normally closed

106
Q

A rectifier is used to?

A

convert alternating current to direct current

107
Q

The run windings of a motor have _____ turns as compared to the start
windings.

A

fewer

108
Q

On a typical split-phase electric motor the start winding circuit is deenergized as it
reaches approximately ____ of its operating speed?

A

75%

109
Q

What component wired in series with the start windings on a single phase
motor will create greater starting torque.

A

a capacitor

110
Q

A three-phase motor does not have

A

start windings

a start capacitor

a start relay

111
Q

A start component that is rated in microfarad would be a

A

capacitor

112
Q

What effect will a higher supply voltage have on the current draw of an
electric motor?

A

it will be higher than it should be

113
Q

With an electric motor running normally the amperage reading would be
called?

A

run-load amperage

114
Q

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?

A

the start winding circuit has an open somewhere

115
Q

What device would be discharged using a 20,000-ohm, 5 watt resistor?

A

capacitor

116
Q

The run-load amperage on an electric motor is typically

A

1/5 that of a full-load amperage

117
Q

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

a pilot duty relay

118
Q

A magnetic coil and electrical contacts are the primary components of this
electrical device?

A

a contactor

119
Q

A magnetic coil, overload protector and electrical contactors are the
primary components of this electrical device

A

a motor starter

120
Q

An electric motor that has an internal overload would have a?

A

a thermal device buried in the motor windings

121
Q

What device could be used as external protection for a motor?

A

a line fuse
a circuit breaker
an external overload

122
Q

What type of motor would a technician switch any two legs on to reverse
the rotation of the motor?

A

Three Phase

123
Q

A technician could install this type of component on a refrigeration system
that has multiplexed circuits to

A

prevent the evaporator temperature on a multiplexed system

from falling too low

124
Q

A technician would set this device by the RLA on the refrigeration
compressors

A

crankcase pressure regulator

125
Q

A technician would set this device by calculating the evaporator
superheat.

A

thermal expansion device

126
Q

What device is used to reduce the suction temperature of the

compressor?

A

desuperheating TXV

127
Q

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

a variable frequency drive (VFD)

128
Q

The EPR valve is installed between the?

A

suction accumulator and the compressor

evaporator and the suction accumulator

129
Q

Which of these devices would be considered a low ambient temperature
head pressure control used on an outdoor unit?

A

fan cycling

130
Q

If a technician wanted to protect a refrigeration system from operating
under excessive head pressure situations he would install a/an

A

head pressure control

131
Q

The following device would use a pressure transducer to sense net oil
pressure, electronic oil safety controllers use a

A

electronic oil safety contro

132
Q

If a technician needed high accuracy it would be best to select a device
that employed the following sensing element if available

A

a thermistor

133
Q

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?

A

automatic pump down cycle

134
Q

.

A

.

135
Q

.

A

.

136
Q

.

A

.

137
Q

.

A

.

138
Q

.

A

.

139
Q

Large or small compressors on parallel compressor racks, which are
usually dedicated to the coldest cases, are called?

A

satellite & booster compressors

140
Q

What is a true statement regarding the operation of a parallel rack
system?

A

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
Q

Why is it important for the oil separator to be sized properly, insulated and
located as close to the compressor as possible?

A

to minimize the chances for refrigerant vapor to condense into
liquid inside the separator

142
Q

The capacity that a parallel rack will have during operation is determined
by?

A

the coldest temperature evaporator

143
Q

On a parallel compressor rack what device is used to control multiple
evaporators?

A

EPR.

144
Q

What can cause the suction pressure on a parallel rack system to run
higher than its setpoint?

A

a higher than design system load

145
Q

Auxiliary contacts would not be used to?

A

Control a crankcase heater

Control an interlock circuit

146
Q

What device would be used to cycle the condenser fans on and off as
system head pressure changes?

A

a reverse acting high-pressure control

147
Q

A device used to damper out compressor torque to the connected copper
piping is a

A

vibration eliminator

148
Q

A device used to maintain a minimum oil condition in a parallel rack
compressor is

A

oil level contro

149
Q

To maintain the correct amount of oil in each compressor on a parallel
rack an oil system would

A

oil separator
oil reservoir
oil level regulator

150
Q

What device is used on an oil system on a parallel to control the pressure
of the oil feeding the
oil regulator?

A

pressure differential valve

151
Q

What is the best method for precharging an oil separator?

A

charge the oil directly into the separator before brazing into
place

152
Q

A decrease in suction pressure of a reciprocating compressor will result in:

A

a decrease in volumetric efficiency

153
Q

For every 1ºF of additional liquid subcooling a systems capacity will be
increased by approximately?

A

1%

154
Q

These lines should be insulated to help maintain subcooling

A

liquid line

155
Q

Additional liquid subcooling

A

reduces the amount of flash gas at the outlet of the TXV

156
Q

What is the purpose of a mechanical subcooling loop on a parallel rack
system?

A

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
Q

Inadequate liquid sub cooling in a system can cause?

A

excessively high evaporator superheat

excessively high discharge temperatures

158
Q

What device would be considered a non-modulating expansion device?

A

a capillary tube

159
Q

A CPR valve is used to protect the compressor from?

A

high load pull-downs

amperage load over RLA

160
Q

What happens to the gauges if there is a high refrigerant charge in a
system using a capillary tube?

A

both the suction and discharge gauges will indicate a high

pressure

161
Q

An overcharge with this type of device will cause a decrease in evaporator
superheat?

A

capillary tube

162
Q

The liquid receiver service valve could be used to?

A

charge refrigerant into the system

remove refrigerant for the system

stop the flow of refrigerant for system pump down purposes

163
Q

A technician me need to bypass this control when charge a system

A

LPC

164
Q

When charging liquid refrigerant into a compressor care must be taken
because?

A

damage to the compressor may occur by liquid slugging

it is easier to overcharge the system

165
Q

Low suction pressure and under cooling can be caused by?

A

undercharged system

166
Q

What type of refrigerants must be charged into a system in a liquid form?

A

zeotropic refrigerants

near azetropic refrigerants

167
Q

A low pressure switch can be used to?

A

control frost build-up on the coil

168
Q

What device is used to shut the compressor off if the suction falls below a
given set point?

A

LPC

169
Q

What device is used to prevent refrigerant migration to the compressor
during the off cycle?

A

a crankcase heater

a pump-down cycle

170
Q

On an ice machine the flush cycle is designed to?

A

remove mineral build-up in the water

171
Q

Carbon filtration is used to?

A

remove chemicals from the water

172
Q

The flaky coating that can build up on the surface of the evaporator on an
ice machine is called?

A

scale

173
Q

How is the ice harvest accomplished on most ice machine?

A

by hot gas defrost

174
Q

What could cause an ice machines capacity in #’s per hour to be reduced?

A

excessive mineral deposits on the evaporator plate

dirty condenser coil

higher than normal entering water temperature

175
Q

Sand and dirt in water are usually easily removed by?

A

filters

176
Q

As its temperature decreases, a/an ____ will decreases its resistance.

A

PTC thermistor

177
Q

What type of valve is used to direct hot gas from the condenser to the
reclaim coil?

A

a three way heat reclaim valve

178
Q

What is the media that is heated by a heat reclaim system?

A

Air & Water

179
Q

Why is a heat reclaim system so important?

A

it allows heat to be recaptured from the refrigerant stream and
reused.

180
Q

What is the function of a timer release solenoid?

A

terminate the defrost cycle

181
Q

What component energizes the electric defrost heater on a 24-hour
defrost timer?

A

a normally open set of contactors

182
Q

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?

A

termination thermostat

183
Q

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?

A

electric defrost

184
Q

What is the BTU output of an electric defrost heater that is rated at 1200
watts?

A

4096 BTU’s

185
Q

What would the best method of defrost be for a fixture that had an
evaporator temperature below freezing but a case temperature above
freezing?

A

off cycle air defrost

186
Q

On a supermarket rack employing hot gas defrost where would the hot
gas solenoid valve be installed?

A

between the discharge line and the oil separator

187
Q

If you find yourself at odds with a confrontational customer, you should

A

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
Q

When entering a customer residential premises you should always

A

place a clean pair of disposable covers over your shoes

189
Q

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?

A

discuss what you have found with the customer and your supervisor so that the
customer can decide whether to authorize the additional repair

190
Q

Which of the following is a required part of the work order?

A

form completed in legible hand writing

complete list of materials used and amount of time spent on the job

191
Q

Getting the customer to sign the work order should be

A

the last thing that you should do before leaving the job

192
Q

Which of the following is a part of your responsibility relative to your work
crew?

A

working safely on the worksite

193
Q

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?

A

refuse the offer politely and if it happens again notify your supervisor of the situation

194
Q

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?

A

request authorization from the customer to stay on the job until it is finished that evening

ua hvac star exam prep (4 decks)

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