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Hvac > Written test 2 100 questions > Flashcards

Written test 2 100 questions Flashcards

1
Q 
which of the following voltages are not safe for a 208-V motor to operate?
a 170 volts
h 220 volts
c 238 volts
d bath a and c
A

d bath a and c

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2
Q

if the voltage supplied to the motor is well below the motor rated voltage, the current draw will be it should be

A

higher than

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3
Q

The voltage tolerance of a standard electric motor is

A

+15%-15%

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4
Q

locked-rotor amperage is normally ________times as great as the nun-load amperage

A

three

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5
Q

Why are explosion-proof motors not normally used on standard equipment?

A

They are too expensive.

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6
Q

motor that should be used in a potentially wet area is a(n)___ motor

A

Drip proof

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7
Q

When referring to motors, to what does the “insulation class” relate?

A

the normal operating temperature of the motor

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8
Q

A sleeve bearing would typically be used in a motor that operates with a

A

light load and where noise is a factor

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9
Q

A slotted screw at the bottom of the bearing housing is called a

A

relief plug

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10
Q

A direct-drive motor is usually connected to a load with a

A

coupling

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11
Q

Grounding straps are required on resilient mounted motors to

A

ground the motor in case of winding failure

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12
Q

The width of a drive belt is classified as

a. large or small
b. narrow or wide
c. A or B
d. 1 or 2

A

c. A or B

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13
Q

The alignment of a motor and the driven mechanism must be done at room temperature and

A

at operating temperature

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14
Q

A motor can burn out if the supply voltage is either too high or too low
True or Fales

A

True

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15
Q

One method a technician can employ to check a motor is to take amperage readings of a motor
(both on and after start-up) and compare them to the motor’s nameplate
on start-up and
a. True
b. false

A

True

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16
Q

The delta transformer has been popular in some locations in the past

a. True
b. False

A

A

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17
Q
  1. A drip proof motor is designed to prevent any lubricating oil from leaving any of the bearings
    a. True
    b, False
A

False

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18
Q

When oiling a permanently lubricated motor, a 20-weight, non-detergent motor oil should be used

a. True
b. False

A

False

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19
Q

Regardless of the type of motor or application, the motor bearings require yearly lubrication.

a. True
b. False

A

True

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20
Q

There is a definite relationship between the speed of the motor and the speed of the blower
a. True
b False

A

True

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21
Q

A motor’s speed is determined by _____

A

number of motor poles

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22
Q

Start wingdings are placed ____

with the run winding

A

slightly out of phase

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23
Q

The start windings have

A

more turns than the run windings

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24
Q

A split-phase has a___

winding and a___winding

A

start, run

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25
Q

when a general duty split phase motor reaches a approximately 75% of its operating speed, the start winding is de-energized by a

A

centrifugal switch

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26
Q

A split-phase motor that has a current relay and a start capacitor is called a(n)___
motor

A

Capacitor Start, Induction Run (CSIR)

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27
Q

When a Capacitor Start Induction Run (CSIR) motor is running and up to speed, what is the total capacitance act on the motor? (Assume the run capacitor is 5 micro farads and the start capacitor is 20 micro-farads, if present.)

A

5 micro-farads

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28
Q

A permanent split capacitor (PSC) motor that is running and up to speed will have the start winding ______

A

energized

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29
Q

When a Capacitor Start, Capacitor Run (CSCR) motor initially starts, what is motor? (Assume the run capacitor is 5 microfarads and the start capacitor is 20 microfarads, if present.)

A

25 microfarads

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30
Q

Capacitors wired in series with the starting winding provide a(n)

A

greater starting torque

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31
Q

The shaded pole motor_

A

has little starting torque

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32
Q

Three phase motors have

A

run windings only

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33
Q

A current magnetic relay opens and closes its contacts based on the

A

Current in the start winding

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34
Q

The starting device usually used on single phase, fractional horsepower motors requiring low starting torque is the

A

current relay

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35
Q

The positive temperature coefficient resistor start device is a type of

A

variable resistor

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36
Q

A permanent split-capacitor motor has a

A

run capacitor only

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37
Q

The magnetic fields generated in the rotor and stator of a motor causes the rotor to be pushed around the shaft.

a. True
b. False

A

False

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38
Q

The heavier the load on an operating motor, the greater the amount of slip.

a. True
b. false

A

True

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39
Q

In order to change the direction of rotation of a split-phase motor, the technician must change the direction of current flow through the start winding.

a. Truc
b. False

A

True

40
Q

The centrifugal switch mounted on the shaft of a split-phase motor has a normally closed contact

a. True
b. False

A

True

41
Q

the contact() in a potential type starting relay arc normally closed

a. True
b. False

A

True

42
Q

Once the start winding and the start capacitor have been removed for the circuit, the motor will continue to operate with only the run winding energized.

a. True
b. False

A

True

43
Q

The microfarad rating of the run capacitor is much lower than that of the start capacitor for any given motor
application
a. True
B.false

A

true

44
Q
  1. A Capacitor Start Capacitor Run (CSCR) motor that is wired with a potential relay will have the start winding energized when the relay’s contacts open.
    a. True
    b. False
A

True

45
Q

The contact(s) in a current type starting relay are normally closed

a. True
b. False

A

False

46
Q

The resistances of the windings in a three phase motor are all equal

a. True
b. False

A

True

47
Q

winding when energized, will generate a magnetic field as there will be current flowing through it.
A. True
b. False

A

True

48
Q

A motor that has copper bars in the rotor is classified as a(n)_______type.

a. True
b. False

A

False

49
Q

The difference between synchronous speed and full load speed is called slip
a true
b. False

A

True

50
Q

The coil of a potential relay has low resistance

a. True
b. False

A

true

51
Q

Charging a refrigeration system refers to

A

adding refrigerant to a system

52
Q

Refrigerant in vapor form is normally put into the system through the

A

suction line

53
Q

When charging a system with vapor refrigerant from a refrigerant cylinder, the cylinder will become

A

Cold

54
Q

Refrigerant in liquid form is normally put into the system through the

A

liquid line

55
Q

When charging liquid refrigerant from a single valve supply cylinder, the cylinder is placed

A

upside down

56
Q

A graduated cylinder charging device is a device that

a. measures refrigerant by volume for precise refrigerant charging
b. has a compensation dial for adjusting for the temperature of the refrigerant
c. often has a heater to keep the refrigerant temperature from dropping when refrigerant is released into the system
d. All of the above.

A

D all the above

57
Q

If 22 oz of refrigerant are to be added to a refrigeration system and the supply cylinder weighs 24 lb. 12 oz. before any is added, what will be the supply cylinder weight after the system has been charged?

A

23 lb 6 0z.

58
Q

If 30 oz of refrigerant are to be added to a refrigeration system and the supply cylinder weighs 26 lb. 4 az. before any is added, what will the supply cylinder weigh after the system has been charged?

A

24 lb 6 oz

59
Q

The factory charge in a split system, using R-22, shows 6 Ib. 8 oz. in the outdoor condensing unit and 2 oz in the evaporator. The 3/8” liquid line contains 0.48 oz. per foot and the 7/8” suction line contains 0.10 oz per foot. The refrigerant lines are 30’ long. What is the correct refrigerant charge for this system?

A

7 lb 11 oz

60
Q

If a critically charged refrigeration system is over charged, which of the following is a likely result?

a. Increased cooling capacity
b. Reduced compressor discharge temperature
c. Increased system efficiency
d. Increased operating pressures

A

. Increased operating pressures

61
Q

Fractionation occurs when

A

some of a blended refrigerant evaporates or condenses before the rest of the blend

62
Q

When charging a refrigeration system with a near-isotropic mixture, what must be done to prevent liquid from entering a system

A

Charge as a liquid through the low side using a restrictor

63
Q

When adding refrigerant in vapor form to an operating refrigeration system, the refrigerant rust be added to the low-pressure side of the system

A

True

64
Q

Missing 65

A

Missing 65

65
Q
  1. When the system pressures are lower than the pressure in the refrigerant tank, such as when the system has just been evacuated or if the system is out of refrigerant, refrigerant can be added to both the high and low pressure sides of the system.
    a. True
    b False
A

true

66
Q

If the tank is a reusable tank, there are no check valves and system refrigerant can enter the tank as long as the system pressure is higher than the pressure in the tank

a. True
b. False

A

True

67
Q

The quickest method to charge a system is to charge only vapor

a. True
b. False

A

False

68
Q

When adding refrigerant in liquid form into the high-side of the system, the system motor/compressor assembly running

a. True
b. False

A

False

69
Q

Using a restrictor, liquid refrigerant can be charged into the low-side of the system with the system operating.

a. True
b. False

A

True

70
Q

One good feature of an electronic charging scale is that it counts upward as refrigerant is removed, to tell the technician how much refrigerant was used

a. True
b. False

A

True

71
Q

A manufacturer’s charging chart may be used when available to determine the correct charge for a system

a. True
b. False

A

True

72
Q

Glide is the range of temperatures/pressures in which a blended refrigerant will condense
a True
b.False

A

True

73
Q

Refrigerant in vapor form is added to an operating system through the High Pressure side of the system
a True
b. False

A

False

74
Q

As refrigerant vapor is removed from a supply cylinder, the pressure in the supply cylinder will fall.
a True
b False

A

True

75
Q

The king valve is used to help technicians perform a number of tasks including taking pressure readings on system and trapping all of the system refrigerant in the receiver to perform system service.
a True
b. False

A

True

76
Q

The best method of leak checking is when the refrigeration system is open to the atmosphere.

A

standing with dry nitrogen pressure of 150 psig in the system

77
Q

When moisture is present in a refrigeration system, it will react with the refrigerant and the oil to form

A

acid

78
Q

Noncondensable gases ____

A

are undesirable in a refrigeration system

79
Q

To pull a vacuum means to

A

lower the pressure in a refrigeration system below atmosphere

80
Q

A compound gauge
a indicates pressures above 14.696 psia
b. indicates pressures in inches Hg below atmospheric pressure
c. is one of two gauges on a typical gauge manifold
d. All of the above

A

d. All of the above

81
Q

A micron gauge is wed to measure

A

absolute pressures below I mm Hg

82
Q

what pressure range does the technician valve off the vacuum pump when evacuating to a deep vacuum?

A

500 to 300 microns

83
Q

Which of the following represents the lowest vacuum?

A

1000 microns

84
Q

A multiple evacuation means that

A

you pull a vacuum on a refrigeration system more than once, allowing refrigerant or nitrogen into the system between each procedure

85
Q

Moisture in a liquid state must be ________ before it can be removed with a vacuum pump

A

Vaporized

86
Q

To insure accurate testing, the best material to use for connecting lines to the vacuum pump and gauge set is

A

copper tube

87
Q

The maximum recommended pressure for leak testing is 150 psig on the low-pressure side of he system

a. True
b. False

A

True

88
Q

Air entering a refrigerant system can eventually lead to compressor failure

a. True
b. False

A

False

89
Q

Clearance tolerances are such that the ordinary clean refrigerant oil can be used satisfactorily in a vacuum pump
a True
b. False

A

True

90
Q

The oil in a vacuum pump should be changed after each time it is used

a. True
b. False

A

True

91
Q

While under a deep vacuum, any liquid water under the ail in the motor-compressor assembly can be removed by operating the compressor motor for several seconds without any adverse effect on the system

a. True
b. False

A

False

92
Q

After repairing a system that has had an electrical motor failure (compressor burnout), it in good field practice to reuse the recovered refrigerant in that system.

a. True
b. False

A

False

93
Q

When using a “standing pressure test for leak-checking, air should never be used since an explosive mixture can be created

true or false

A

True

94
Q

Sludge is produced when moisture, acid, and oil are present in the system
a True b false

A

True

95
Q

Only two substances should be in the refrigeration system for proper operation. They are water and oil
a True
B false

A

True

96
Q

When all else fails, read the manual.

a. True
b. False

A

True

Hvac (29 decks)

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