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UA HVAC Star Exam Prep > UA Local 140 Practice Test 1 > Flashcards

UA Local 140 Practice Test 1 Flashcards

1
Q

. Which of the following is true when there is excessive vibration of rotating machinery?

A

It may lead to fatigue failures

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2
Q

Which is the best practice to follow when one bearing fails is a multiple bearing application?

A

Replace all bearings

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3
Q

Thrust loads are____ to a shaft.

A

Parallel

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4
Q

When installing split tapered bushings, where should you apply anti-seize lubricant?

A

none of the parts

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5
Q

Which is the final step in installing a pillow block bearing?

A

tighten bearings to shaft

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6
Q

The mechanical seal in a centrifugal pump is necessary to prevent which of the following events?

A

fluid leaking out around the shaft

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7
Q

If a mechanical seal has just been replaced and the pump leaks slightly at start-up, which step should you take

A

a. allow the pump to continue running for a short period to see if the leak stops

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8
Q

How should the belts in a multiple V-belt application be replaced?

A

as a set

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9
Q

While performing a visual inspection of a belt driven fan, which of the following is NOT a requirement of the
inspection?

A

manufacturer of the belt

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10
Q

Using a belt tensioning tool, which factor is NOT taken into account when adjusting belt tension?

A

number of belts

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11
Q

The horsepower of the motor is transferred from the V Belt to the fan pulley where on the belt?

A

the sides of the belt

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12
Q

A belt drive on a motor driven fan has a drive sheave of 3” pitch diameter on the motor. The sheave of the fan shaft has a pitch diameter of 5”, when the motor speed is 1720 RPM, what is the fan speed?

RPM of drive=diamerterof driver X RPM of driver
Divided by Diameter of driven

A

1032 RPM

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13
Q

Which of the following is the major cause of high speed rotating equipment failure?

A

imbalance and misalignment

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14
Q

Which is the first step of shaft alignment of a direct drive motor?

A

Angular in elevation view

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15
Q

Which tool would not be used to align a pump?

A

voltmeter

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16
Q

Which is the first step of shaft alignment of a direct drive motor?

A

flexible base

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17
Q

Which of these statements is TRUE of a coupling which is NOT properly aligned?

A

it will almost certainly fail more quickly than it should and could wear out

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18
Q

Which of these statements is true of coupling guards?

A

they should be kept in place for the life of the equipment

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19
Q

A tire style coupling is commonly used on which of these?

A

cooling towers

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20
Q

Which of these is the tool to use to move a coupling half that is seized on the motor shaft?

A

hammer with softening tool

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21
Q

Which of the following times situations does NOT require a re-check of the pump coupling alignment?

A

after a motor and pump are at the normal operating temp

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22
Q

Potential difference refers to the energy difference in electrons between two reference points measured in
which type of unit?

A

volts

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23
Q

The basic law for current is a series circuit states that amperage is______ parts of the circuit.

A

the same in all

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24
Q

Operation of the potential relay is based on which of these principles?

A

motor develop counter EMF

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25
25. Since checking will be done with live circuits, the service technician must observe all the necessary precautions to avoid danger of
electric shock and damage
26
Which of these is the type of electrical diagram most commonly used for understanding sequence of operation for HVACR equipment?
schematic
27
How many BTU's per hour will be provided by one watt of electrical energy in a resistance heater.
3.413
28
Starting relays are NOT used by which of the following motors?
PSC
29
When two run capacitors having values of 15 MFD and 10 MFD are connected in parallel, what is the combined value?
25 MFD
30
If a split phase motor turns in the wrong direction, its direction of rotation can be reversed by this action.
interchanging the starting winding leads
31
Why is it necessary to use a static wrap when replacing circuit boards?
to prevent component damage
32
Which tool is used to diagnose a de-energized circuit board?
ohmmeter
33
Under which of the following conditions should you NOT use a megger?
within a deep vacuum
34
Which of these is the correct range that should be used on a multimeter when checking current?
a high range to start, then working down
35
Which of the following instruments is used to simulate the analog input to a variable frequency drive?
signal generator
36
Which of the following is NOT an advantage of variable frequency drives?
low initial equipment costs
37
On a variable air volume system, if the static pressure goes up, the VFD should
ramp down
38
When will an overload contact on a motor starter open?
when excessive current flows thru the motor
39
Which is a difference between a motor starter and a contactor?
a starter has overload protection
40
A full voltage starter energizes which of these?
all contactors
41
Which of these should the contactor have when only one of the contactors on a control panel can be closed at a time?
mechanical interlock
42
Which of these is TRUE of contactors?
they are similar to relays
43
Which of these acronyms will be found on the label of a three phase contactor?
TPST
44
For which purpose is a time delay relay used.
to prevent the compressor from short cycling
45
While troubleshooting, it is found that on a call for cooling, the voltage across a potential relay's contacts remains 0 volts. the compressor then cycles on its internal overload. which of the following is a possible explanation?
closed contacts in the potential relay
46
When the motor of a two-wire spring return actuator is operating, what is happening with the spring?
it is being wound up
47
During flow switch installation the paddle must be
fitted to the pipe
48
Which of the following instruments is used to verify water flow across the chiller barrel?
differential pressure switch
49
A thermistor has a wide change in resistance for a small change in which of the following?
temperature
50
Outdoor reset of hot water temperature for heating results in which of the following?
hottest water during the coldest weather
51
A boourdon tube pressure gauge reads 145 psig. if local atmospheric pressure is 14.5 psia what is the absolute pressure indicated by the gauge?
159.5 145+14.7psia
52
Which of the following devices changes energy from one form to another?
transducer
53
Where is a bellows used?
in both pressure and temperature controllers
54
a photo detector converts light to a
electrical signal
55
To lessen short cycling, which of the following adjustments could be made to the pressure control?
widen the differential
56
Oil failure safety switches, refrigerant dual pressure switches, and overload relays in motor starters are classified as which type of controls?
safety controls
57
For which purpose are lockout relays used in air conditioning systems?
prevent compressor short cycling
58
Which is the proper switch to use to make the pneumatic thermostat on an air conditioning system turn the fan motor on and off?
P-E
59
Which of the following is an analog input?
temperature sensor
60
Which of the following is an analog output?
VFD speed control
61
What is the desired value of a controlled variable called?
setpoint
62
Which of these are two basic types of low water cutoff controls?
float type and electric probe type
63
An increase in the latent load across an evaporator will cause which of the following changes in the suction and discharge pressure?
there will be an increase in suction and discharge pressure
64
Saturated liquid line pressure minus liquid line temperature is equal to which of these?
subcooling
65
Low superheat or a liquid floodback to the compressor could be caused by all EXCEPT which of the following?
undercharged system
66
Which of these reflects the temperature and the state of the refrigerant leaving the compressor?
hot vapor
67
Which of these results can be expected if too much refrigerant is being fed to the evaporator?
the superheat will be low
68
Which of the following gasses must never be used to pressureize or leak test a refrigeration system?
oxygen
69
Which of the following gasses must never be used to pressurize or leak test a refrigeration system?
30%
70
What is the purpose of using a Nitrogen purge when repairing a leak?
prevent copper oxide from forming inside pipe
71
Which is the most accurate tool to use when measuring evacuation levels?
micron gauge
72
Which of the following is NOT a way to speed up evacuation?
smaller gauge hoses
73
During a standing vacuum test, the system goes from 500 microns to 2,000 microns and ten stops. Which of the following is the most likely cause? a. leak in the system
moisture in the system
74
Which is the issue that brought about the CFC venting laws?
reduction of the Ozone layer
75
How many pounds of refrigerant can a recovery cylinder safely hold if the following is stamped on the side of the cylinder? TW = 18.2 lbs WC = 47 lbs
37.5lbs
76
Which is the fastest way to totally recover refrigerant?
push pull method
77
Bubbles in a refrigerant sight glass are an indication of what condition?
there is vapor mixed with the liquid
78
When calculating subcooling for an HFC refrigerant with a large temperature glide, which column on the pressure/temperature chart is used?
bubble point
79
For systems that use capillary tube for metering devices, which of the following is the best method for checking proper refrigerant charge?
superheat
80
For a compressor having a lubricating oil pump, the net oil_pressure is equal to pressure.
oil pump discharge pressure minus compressor suction
81
Discoloration of a compressors valve plate and/or valves may indicate which of these conditions?
contamination or overheating
82
Refrigerant is compressed through a scroll compressor from the of the scroll(s)
outside to the center
83
What is the purpose of a slide valve on a helical rotary screw compressor?
to provide capacity control
84
Evaporator approach on a centrifugal water chiller is determined by calculating the difference between
entering and leaving evaporator water temperature
85
In the hot as bypass control method, which system component is bypassed?
condenser
86
In addition to evaporator pressure, the thermostatic expansion valve has which two operating pressures?
spring and bulb pressure
87
Where is the expansion valve located in the refrigeration system?
in the liquid line at the entrance to the evaporator
88
If the thermal bulb on the TEV comes loos from its mounting at the outlet of the evaporate, which of the following will occur?
the valve will open, feeding more refrigerant into the evaporator
89
What is the acceptable temperature drop across a liquid line filter drier?
less than 2 degrees/0
90
The amount of heat rejected by the condenser of an air conditioning system is typically______ the amount of heat absorbed in the systems evaporator.
25%
91
Which solution should be used for chemically cleaning a condenser?
an inhibited acid
92
The amount of heat removed by evaporating one pound of water in an evaporative cooling tower is approximately how many Btu(s)?
1000
93
On a mechanical draft cooling tower, what dictates the coldest basin water temperature available?
outdoor wetbulb
94
Which of the following does NOT need to be considered when converting from a HCFC to a HFC refrigerant in a system?
thickness of the line tubing
95
An acid test kit is used to test the acidity of which of the following?
oil
96
Which of the following is a disadvantage of a VRF system?
does not allow for future expansion
97
Which is true of the heating capacity of and air to air heat pump
it decreases as outdoor air gets colder
98
On an intermittent pilot system, when is the pilot light on?
through the main flame cycle
99
The purpose of combustion testing is to perform all except which of the following?
condition air through the air handler
100
Which of the following would cause continuous addition of makeup water to a radiant heating system?
leak in system

UA HVAC Star Exam Prep (4 decks)

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