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Refrigerant 2 > Refrigerant 2 > Flashcards

Refrigerant 2 Flashcards

1
Q
  1. What is the minimum allowable refrigerant velocity in a reduced discharge riser?
A

1000-1500 fpm

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2
Q

What is the function of the “p” trap in vapour risers

A

Assists oil movement

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3
Q

What is the correct method to transfer HFC 404A for a refrigeration system?

A

. Removed as a liquid from cylinder and flashed into the system using a refrigeration manifold

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4
Q

When is a crankcase pressure regulator set up?

A

After defrost cycle has terminated and compressor has started

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5
Q

What pressure shall be used to calculate the superheat setting of the evaporator when a TXV is used as the metering device?

A

b. Evaporator outlet pressure near the sensing bulb

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6
Q

Defrost may be initiated by:

A

Time, temperature or pressure

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7
Q

Defrost may be terminated by:

A

Time, temperature or pressure

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8
Q

Calculate the total “u” factor of a freezer wall constructed of the following: 6” of polyurethane; having an “R” value of 6.25 per inch
8” concrete; having a “C” factor of 0.58 Btu/(hr)(ft2)(°F)
5/8” fire rated gypsum board; having a “u” factor of 3.2 Btu/(hr)(ft2)(°F).

A

.0253 Btu/(hr)(ft2)(°F).

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9
Q

What heat load value is unique when cooling fresh fruit and vegetables?

A

Heat of respiration

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10
Q
  1. The oil pump in a large semi hermetic compressor is located where?
A

on the crankshaft end

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11
Q

What type of TEV bulb charge is required on a large tonnage AC rooftop unit to reduce compressor overloading at startup under high load conditions?

A

Vapour charged

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12
Q

Off Cycle Defrost for a single circuit system, involves:

A

condensing unit off and evaporator fan on

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13
Q

Electric Defrost for a single circuit system, involves:

A

condensing unit off and evaporator fan off

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14
Q

Hot Gas Defrost for a multi circuit system, involves:

A

condensing unit on and evaporator fan off

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15
Q

Where is the Evaporator Pressure Regulator located

A

Outlet of the higher temperature evaporator

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16
Q

What type of oil used in stationary refrigeration and air conditioning systems will more readily absorb moisture when the container is opened?

A

Polyolester oil

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17
Q

walls of a building are 20’ high and 200’ long. The drywall has an R value of 0.5, the insulation is R10, the outside polystyrene board is R4 and the outside finish is R0.5. The indoor temperature is 72ºF and the outdoor design temp is -5ºF. Calculate the heat loss through the wall.

A

20,533 Btu/hr

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18
Q

a receiver is located in a location that may become colder than the evaporator

A

Thermostatically controlled heater elements are attached to the surface area of the receiver shell and shell is insulated

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19
Q

What is the effect on a system when the liquid line solenoid valve is installed backwards?

A

System won’t pump down

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20
Q

Where should the liquid line solenoid valve be installed?

A

. In the liquid line after the liquid line filter drier

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21
Q

What is the result when the TXV loses the charge in the sensing

A

Increase in evaporator superheat

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22
Q

Where should the TXV bulb be located for best sensing results?

A

. Evaporator outlet and placed to avoid effects of oil temperature

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23
Q

What is the correct mounting procedure of the thermostatic element bulb to ensure proper control of the TEV?

A

Clean evaporator outlet tubing after suction header, secure with similar metal clamp and insulate

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24
Q
  1. What is the purpose of the fan delay after a defrost cycle?
A

Allow moisture to drip off and the remainder to solidify on the coil

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25
Q

What is the term given to the device within the time clock that will cause the defrost cycle to end before its time

A

Defrost termination solenoid

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26
Q

What is the amount of sub cooling provided within a standard receiver?

A

0F

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27
Q

When will the king valve on a receiver be completely front seated?

A

When pumping refrigerant out of the liquid line

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28
Q

What happens to a reciprocating compressor when the suction service valve is completely front seated?

A

Compressor crankcase pressure should draw into a vacuum if the low pressure switch cut out is set low enough

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29
Q

The manifold gauge that shall be used to measure suction pressure is called

A

Compound guage

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30
Q
  1. What is the unit of measure for velocity?
A

Fpm

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31
Q

What two temperatures were measured by the electronic temperature control in the refrigeration lab

A

Box and coil

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32
Q

What type of input is used by the JCI MR4 and/or Omnistat for defrost termination?

A

Variable / analog

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33
Q

What switching action is used by a three-phase compressor j?

A

Tpst

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34
Q

What is the function of the low pressure switch used in the refrigeration lab to control the compressor

A

Recycling Pump down

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35
Q

What was the purpose of the delay on make timer in a recycling pump down control

A

Minimum off cycle for the compressor

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36
Q

What is the control voltage used in the refrigeration lab for the load switching components (relay and contactor)?

A

208vac

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37
Q

What voltage is required to power the Omni stat in this lab application

A

120vac

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38
Q

How many contactor poles were required for the single phase evaporator fan control in the low temp coil

A

2

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39
Q

What device is connected to the X & N terminal strip on the evaporator

A

Defrost termination thermostat

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40
Q

How many poles were required to disconnect the single phase defrost heater in the refrigerated box safely

A

2

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41
Q

How should all electrical loads be isolated when not in use for extended periods of time?

A

b. Tagged and locked out

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42
Q

Which is the pressure drop value of venturi and orifice type distributors

A

15 psi venturi and 25 to 35 psi orifice

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43
Q

Which TXV port design is intended for operation with floating head pressure

A

Balanced port

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44
Q

Under what condition would the refrigeration lab compressor lock out and not automatically restart

A

High pressure

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45
Q

Which force will close the compressor contactor?

A

Magnetic

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46
Q

What is illustrated by the pictorial electrical schematic

A

Location of electrical components

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47
Q

What is the function of a ladder electrical schematic

A

Sequence of operation

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48
Q

What is the purpose of the suction line trap at the base of a riser

A

Oil return

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49
Q

What is the term given to the device that held the pipe hanger to the beam

A

Beam clamp

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50
Q

Why was the electrical current draw higher on two of the lines feeding the compressor in the refrigeration lab

A

Single and three phase loads

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51
Q
  1. What tool(s) are required to set up a CRO?
A

Allen wrench, compound gauge & amp meter

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52
Q

Where is the refrigerant heat exchanger installed to improve sub cooling

A

Suction and Liquid

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53
Q

Which is the function of the suction /liquid heat exchanger in the refrigeration piping system

A

Sub cool refrigerant in liquid line
Superheat refrigerant in suction line
Increase NRE

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54
Q

The direct expansion shell and tube evaporator, water circuit can be cleaned by

A

Chemical cleaning

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55
Q

What happens to the refrigerant within the condenser

A

. De-superheated, condensed and sub cooled

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56
Q

Condensers must reject the heat from ____________when open drive compressors are used ?

A

Evaporator, suction line and compression

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57
Q

Which is the theoretical condenser ton for a reciprocating compressor

A

1.25 times evaporator ton

58
Q

What is the result of increasing condenser pressure?

A

Higher pressure drops across TXV

59
Q

. When an evaporator is installed 60 feet below the condenser what is the effect on the nominal tonnage of a TXV

A

b. Increase in nominal tonnage

60
Q

What is the recommended maximum suction line temperature entering a compressor with a SST of 39 ° F

A

65° F

61
Q

When the suction line is covered in ice it is an indication of

A

Suction line is below 32° F

62
Q

What is the purpose of the suction line accumulator?

A

Protect compressor against refrigerant flood back

63
Q

The result of installing a suction accumulator backwards is

A

Loss of oil in compressor

64
Q

Insulating a suction accumulator will

A

Decrease the effectiveness of the accumulator when installed in a warm mechanical room

65
Q

Accumulators return oil to the compressor by utilizing a

A

Venturi orifice

66
Q

What type of float is found in an oil separator?

A

. High side float

67
Q

Insulating an oil separator is required when

A

When a heat tape is used around the separator to prevent off cycle migration in a low ambient condition

68
Q

What is the result of the float failing because of a leak, in an oil separator?

A

Compressor will eventually shut off on oil failure

69
Q

To protect the compressor from off cycle migration what component(s) can be included in the design when low ambient conditions are a factor

A

a. Crankcase heater
b. Solenoid valve in the oil return line from the oil separator
c. a&b

70
Q

What two pressures are sensed by the OPFC?

A

Compressor sump and oil pump discharge

71
Q

The OPFC pressure differential is measured in units of

A

psi

72
Q

What is the function of the “L & M” terminals found on a OPFC?

A

Control circuit for compressor

73
Q

When using an ohm meter to check a conventional oil pressure failure control between the 240 and 120 terminal what is the expected value, if the control is new?

A

1000 Ω

74
Q

When using an ohm meter to check a conventional oil pressure failure control between the L and M terminal what is the expected value if the control is new?

A

0Ω

75
Q

When using an ohm meter to check a conventional oil pressure failure control between the 240 and 2 terminal what is the expected value of a new control?

A

> 1000 Ω

76
Q

control action of the condenser fan cycling control is

A

Reverse acting

77
Q

What is the most correct melting temperature of B Cup 15 as per ANSI

A

> 1100 ° F

78
Q

. When a combination dual pressure control having manual reset is installed, the low side pressure switch is used as a/an

A

. Depends on application in control sequence

79
Q

What are three pressures used to control superheat in an

A

Evaporator, spring, & bulb

80
Q

What are the two basic valve designs used in a reciprocation compressor

A

. Ring and reed

81
Q

. Comfort cooling systems which use hot gas bypass to the evaporator inlet require the use of an __________ when installed with an orifice plate distributor a.

A

. Auxiliary side connector T

82
Q

Compressors that use a method of ___________for capacity control are more energy efficient than a compressor that use another form of capacity control

A

Suction valve lifting or suction cut off

83
Q

What procedure is used to verify rotation, prior to startup, of a 3 phase compressor?

A

use a phase sequence indicator on the line side of the starter

84
Q

The thrust bearing is used to absorb the________ energy exerted by the crankshafT

A

Parallel

85
Q

Paul’s signature saying

A

Does that make sense

86
Q

The windings of a semi-hermetic motor are located in the

A

Stator

87
Q

The windings of an open drive compressor drive motor are cooled by

A

Ambient air

88
Q

The coil of a normally closed lock out relay is wired

A

in parallel with the safeties and in series with the load relay

89
Q

The tool used to verify the winding insulation is the

A

Meg-ohm meter

90
Q

The capacitor in a PSC causes a ______angle shift between the voltage and current

A

Phase

91
Q

. What is the effect on a refrigeration system if the compressor is oversized for the application

A

Low suction pressure

92
Q

What is the effect on the refrigeration system if the TXV is undersized

A

High super heat

93
Q

What is the purpose of the external equalizer port on a TXV

A

. Compensate for high evaporator pressure drop

94
Q

What is unique about the relay used in a NC lock out circuit

A

High impedance

95
Q

A 24 VAC control circuit utilizes the N/C LOR strategy and the system has locked out on high pressure the voltage drop across the coil of the LOR relay is
approximately_____________

A

20 VAC

96
Q

When the N/O LOR contacts are not used in a N/C LOR circuit the LOR can be reset by _____________________

A

All of the above

97
Q

What is the purpose of a recycling pump down circuit

A

Minimize off cycle migration

98
Q

What is the purpose of a non recycling pump down circuit

A

Prevent short cycling of the compressor

99
Q

What device is controlled by the “3” terminal on a defrost time clock

A

Defrost heater

100
Q

What device is controlled by the “4” terminal on a defrost time clock?

A

Compressor contactor

101
Q

What device is connected to the “1” terminal and the “3” terminal on a defrost time clock

A

Defrost heater
And Time clock motor

102
Q

What term describes the switching action of the time clock contacts when the defrost heater and compressor control circuit are the same voltage?

A

Spdt

103
Q

What device is connected between the “1” terminal and the “N” terminal on a time clock?

A

Time clock motor

104
Q

What device can be connected to the “N&X” terminals on a defrost time clock?

A

Low pressure control

105
Q

Is the Omni stat a time of day timer (TOD) or a cycle timer?

A

. Cycle timer

106
Q

Which statement is correct regarding the vacuum pump

A

The gas ballast is turned counterclockwise one turn prior to start up and then clockwise 1 turn at 3,000 µm

107
Q

The temperature range for a defrost termination and fan delay “klixon” is ____.

A

55 º F and 25 º F

108
Q

What type of relay switching action is available on the A 419 temperature control

A

Spdt

109
Q

What is the switching action of the relay required for the non recycling pump down control that provides a holding circuit and separate contacts for the compressor circuit?

A

Dpdt

110
Q

When would two low pressure switches be used on a refrigeration system

A

Operator and safety switch

111
Q

The NO lock circuit normally requires a _______ to start the equipment

A

Momentary contact

112
Q

Scr are found in what

A

Soft start

113
Q

~>|~ what side is anode and what side is cathode on diode

A

Left is anode right is cathode

114
Q

When an air cooled condenser is utilizing “condenser flooding” refrigeration pressure regulators to maintain head pressure what component is also required?

A

Receiver

115
Q

Condenser flooding is accomplished using the following components

A

ORI, ORD and receiver

116
Q

ORI regulators used in condenser flooding applications are similar in operation to the _______________ regulator.

A

Evaporator pressure

117
Q

The ORD regulator opens on a differential in pressure between the ________ & ________

A

Compressor and receiver

118
Q

Condenser flooding may require condenser fan control through the use of

A

Temperature controls
And Pressure Controls
And VFD

119
Q

Sensible cooling of air is calculated by the following

A

Q = CFM x 1.08 x ΔT

120
Q

Evaporator approach is the difference between the

A

. Leaving air or water temperature and SST

121
Q

Total air cooling load can be calculated by the following

A

Q = CFM x 4.50 x Δh

122
Q

If a suction line is 7/8” or smaller, the sensing bulb is generally located:

A

at the 12 o’clock position

123
Q

What procedure is required in order to reduce evacuation pull down time?

A

increased hose size and increase space temperature

124
Q

Insulation on piping is used to:

A

Prevent refrigerant from picking up sensible heat

125
Q

Which method is used to prevent oxidation within piping during brazing

A

purge with near inert gas

126
Q

How much cooling is required to turn 10 pounds of steam at 214°F in to ice at 30°F

A

12,960 Btu’s

127
Q

What is the spring pressure setting of a TXV having the following conditions? R-22, SST = 40º F, Evaporator outlet temperature is 52º F

A

19 psi

128
Q

If a unit cooler had 4 fans rated at 250 watts, how many Btu’s of heat energy would there be?

A

3413 btu’s

129
Q

The EPR valve is:

A

located after the evaporator to prevent the evaporator pressure from decreasing below set point

130
Q

The amount of slope in a 40 ft. horizontal refrigerant vapour line should be:

A

2”

131
Q

A 100 ton system maintains a 40°F SST. The enthalpy of the refrigerant entering the evaporator is 50 Btu/lb and the enthalpy entering the suction line is 110 Btu/lb. How many pounds of refrigerant are circulated?

A

333 lb/min

132
Q

The CPR valve is:

A

located before the compressor to prevent overloading

133
Q

What is the test pressure used on a refrigeration system component when performing a pneumatic pressure test?

A

At 110% component design pressure

134
Q

Which family of refrigerants would be considered azeotropes?

A

R-500

135
Q

An R-134a system has a TEV with a spring pressure of 9.5 psi, an evaporator pressure of 30.5 psig. Calculate the superheat?

A

10°F

136
Q

The entrance door frame of a walk-in freezer requires:

A

a heater

137
Q

Which method of starting provides the highest starting torque?

A

Across the Line

138
Q

What is the voltage unbalance for the following?
L1 – L2 = 197 volts, L1 – L3 = 208 volts, L2 – L3 = 201 volts

A

3%

139
Q

. What are the terminal connections for a dual voltage motor wired in low voltage, Part Winding Start?

A

1MC T1 – T1, 1MC T2 – T2, 1MC T3 – T3, 2MC T7 – T7, 2MC T8 – T8, 2MC T9 – T9

140
Q

What is the sequence for a wye delta start, closed transition?

A

S in, 1M in, 1A in, S out, 2M in, 1A out

141
Q

What are the terminal connections for a dual voltage motor wired in high voltage delta

A

1MC T1 – T1 – T12, 1MC T2 – T2 – T10, 1MC T3 – T3 – T11, T4 – T7, T5 – T8, T6 – T9

Refrigerant 2 (1 decks)

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