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Air-Conditioning Systems > DeWalt HVAC Air Conditioning > Flashcards

DeWalt HVAC Air Conditioning Flashcards

1
Q

The Fahrenheit scale is based on boiling water at sea level at what temperature?

A

212°F

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2
Q

Zero pounds gauge corresponds on the absolute scale to:

A

14.7

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3
Q

Hidden heat in refrigeration work is referred to as:

A

Latent heat

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4
Q

Absolute zero on the Fahrenheit scale is:

A

-459°F

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5
Q

A ton of refrigeration is a unit equal to:

A

12,000 BTU per hour

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6
Q

The heat used to change a liquid to a gas is called the latent heat of:

A

Vaporization

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7
Q

A thermometer is said to “sense” what?

A

Sensible heat

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8
Q

Five pounds of water is heated by 2°F. How many Btu were added to the water?

A

10 BTU

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9
Q

The amount of heat required to melt 1 pound of ice at 32°F is:

A

144 BTU

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10
Q

After all the liquid has been changed to vapor superheat is ____.

A

added

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11
Q

Subcooling is ____ added or removed in changing the temperature of a liquid.

A

heat

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12
Q

The saturation temperature is the same as the ____ ____ and boiling temperature.

A

condensing temperature

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13
Q

Cold is:

A

A relative term with no specific temperature

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14
Q

As the pressure over a liquid is lowered:

A

The boiling point of the liquid decreases.

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15
Q

As heat is added to a substance:

A

The molecules move faster.

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16
Q

The amount of heat it takes to change the temperature of 1 pound of a substance by 1°F is called:

A

Specific heat

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17
Q

The specific heat of a substance changes when the:

A

substance changes state.

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18
Q

A half-filled cylinder of refrigerant at 80°F will be:

A

Saturated

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19
Q

The air you are breathing is:

A

Superheated

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20
Q

The three methods of heat transfer are:

A

Conduction, convection, and radiation

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21
Q

As a gas is compressed:

A

Temperature and pressure increase.

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22
Q

When compressed enough and then cooled, a gas will:

A

Condense

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23
Q

The condensing temperature and the _____ temperature mean the same thing.

A

saturation

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24
Q

The evaporator is a:

A

Low-pressure component

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25
Q

The two components that contain coils are:

A

Condenser and evaporator

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26
Q

Refrigerant vaporizes in the:

A

Evaporator

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27
Q

The two components that divide the high-pressure side from the low-pressure side of a system are the:

A

Compressor and metering device

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28
Q

The pipe that connects the evaporator to the compressor is the:

A

Suction line

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29
Q

The pipe that connects the compressor to the condenser is the:

A

Discharge line

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30
Q

Which one of the following refrigerants would be used with POE oil?

A

R-410A

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31
Q

The discharge line temperature of a reciprocating compressor should never be allowed to exceed how many degrees Fahrenheit?

A

225°F

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32
Q

Refrigerant becomes superheated in the:

A

Evaporator, suction line, and compressor

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33
Q

Refrigerant is in its saturated state in the:

A

Condenser

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34
Q

The temperature-pressure chart works:

A

Where refrigerant is saturated

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35
Q

Which service valve should never be front-seated while the compressor is operating?

A

Compressor discharge service valve

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36
Q

How many microns are there per inch of mercury?

A

25,400 microns/inch

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37
Q

A manifold gauge set is properly attached to the suction and discharge valves on a compressor. In order to read the high- and low-side pressures of the system, what position should the service valves on the compressor be in?

A

Midseated

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38
Q

A manifold gauge set is properly attached to the suction and discharge valves on a compressor. In order to read the high- and low-side pressures of the system, what position should the gauge manifold valves be in?

A

Fully clockwise

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39
Q

A 125-pound cylinder of R-22 is stored in a room at 80°F. The pressure in the cylinder should be:

A

144 psig

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40
Q

Vacuum pressures are measured in:

A

Both inches of mercury and microns

41
Q

The condenser gives up:

A

Sensible and latent heat

42
Q

What is the purpose of a valve installed on the high side of the system and which causes the condenser to flood with liquid refrigerant under certain circumstances?

A

It controls the head pressure during periods of low outside ambient temperatures.

43
Q

A thermostatic expansion valve controls evaporator:

A

superheat

44
Q

An automatic expansion valve directly controls evaporator:

A

pressure

45
Q

The oil failure control is operated by the:

A

oil pump discharge pressure and the suction pressure

46
Q

A system is running constantly and not cooling the space. The suction line at the compressor is cold and sweating. These symptoms seem to indicate that the:

A

air filter is restricted and/or the evaporator is dirty.

47
Q

A frosted suction line on an air conditioning application indicates:

A

The suction line temperature is below the dew point of the ambient air and at or below 32°F.

48
Q

An oversized air conditioning system may cause:

A

The system to short-cycle

49
Q

Flooded starts on a compressor can be the result of:

A

Refrigerant migration
Refrigerant overcharge
A burned-out crankcase heater

50
Q

An air conditioning system has adequate airflow over both the evaporator and condenser. The low side has a superheat of 60F°, and the condenser subcooling is 25°F. What is most likely wrong with this system?

A

It has a restriction in the liquid line.

51
Q

Low airflow over a residential split system air conditioning evaporator can cause:

A

Liquid floodback to the compressor

52
Q

As the pressure on a liquid is increased, the vaporization temperature of the liquid:

A

Increases

53
Q

An oil separator must be mounted:

A

Level

54
Q

Which metering device controls evaporator pressure?

A

Automatic Expansion Valve

55
Q

The purpose of the external equalizer on a thermostatic expansion valve (TEV) is to:

A

equalize evaporator pressure drop with respect to the TEV

56
Q

The higher the MERV rating of a filter-drier, the:

A

MERV does not apply to filter-driers.

*They only apply to air filters.

57
Q

Zeolite is used with:

A

Refrigerant filter-driers

58
Q

Vacuum pressures are measured in:

A

Microns
Millimeters of mercury
Inches of mercury

59
Q

The number 25,400 relates to:

A

microns/inch

60
Q

The general rule of thumb for airflow is:

A

400 cfm/ton

61
Q

A double-suction riser is used to:

A

Improve oil return as system capacity changes

62
Q

A service technician measures a return air temperature of 80°F and a supply air temperature of 55°F. What, if anything, may be wrong with this air residential split system air conditioning unit?

A

Low on evaporator airflow

63
Q

The normal compression ratio for a typical comfort air conditioning application should be in the range of:

A

2.75 to 3.75

64
Q

All else being normal, if a system shows a high low-side superheat with high condenser subcooling, what is most likely the problem?

A

A partial refrigerant restriction

65
Q

All else being normal, if a system shows a low low-side superheat with high condenser subcooling, what is most likely the problem?

A

Refrigerant overcharge

66
Q

All else being normal, if a system shows a high low-side superheat with low condenser subcooling, what is most likely the problem?

A

Refrigerant undercharge

67
Q

A grille equipped with a damper control is called a:

A

register

68
Q

A pressure relief valve is:

A

Direct pressure acting

69
Q

A parallel compressor system in which both the crankcase oil level and the refrigerant gas pressure are equalized is a(n):

A

Double pipe crankcase equalizer system

70
Q

In a direct expansion chiller used on air conditioning applications, the refrigerant is on what side of the tubes?

A

In the tubes

71
Q

The total minimum open area for air to flow through on a supply air register is called the:

A

Free area

72
Q

Which type of copper tubing has the thickest wall?

A

Type K

73
Q

What is the gross weight of a refrigerant cylinder?

A

The weight of the cylinder plus the weight of the refrigerant

74
Q

What does an anemometer measure?

A

Feet

75
Q

The term “induced draft” most likely refers to a:

A

type of cooling tower

76
Q

What fitting should be used to connect ¼” copper tubing to a ¼” internal pipe thread opening on a compressor crankcase?

A

A half union

77
Q

Which of the following compressors has the fewest moving parts?

Rotating vane rotary

Fixed vane rotary

Scroll

Reciprocating

A

Scroll

78
Q

A hot liquid line with a low to normal high-side pressure is an indication of

A

An undercharged system

79
Q

Air and water are directed counterflow so as to:

A

Gain the greatest amount of heat transfer

80
Q

Which of the following applications is not a mechanical cooling system?

Cascade system

Reciprocating compression system

Evaporative cooling

Centrifugal compression system

A

Evaporative cooling

81
Q

A compressor is short cycling. Which of the following would not be the cause?

Low pressure controller differential set too close

Automatic reset high-pressure control differential set too close

Low refrigerant charge

Leaking compressor suction valve

A

Leaking compressor suction valve

82
Q

The position of the valve stem on the suction service valve is normally:

A

Fully backseated

83
Q

Of the three fundamental fan laws, one states that the power varies by the ______ of the speed.

A

cube

84
Q

Abnormally low suction pressure can be caused by which of the following?

Dirty air filter

Partially restricted filter-drier

Shortage of refrigerant

Any or all of the above

A

Any or all of the above

85
Q

Which of the following compressor oil types is generally considered the most compatible with HFC refrigerants?

POE

AB

Mineral

Vegetable

A

POE

86
Q

The factor determining the correct quantity of air for each room in a building is the:

A

calculated heat load for each room

87
Q

Refrigerant 22 is classified as a(n):

A

A-1 refrigerant

88
Q

Which of the following combinations of instruments can be used to measure airflow in cfm on an electric furnace?

A thermometer, ammeter, and voltmeter

A thermometer, tachometer, and voltmeter

A tachometer, pitot tube, and ammeter

A gauge manifold set, thermometer, and voltmeter

A

A thermometer, ammeter, and voltmeter

89
Q

A rotating vane anemometer measures:

A

feet

90
Q

A lockout relay is also called a(n):

A

Both an impedance relay and a reset relay

91
Q

A lockout relay can be reset by:

A

De-energizing the main power
Pushing the reset button
Turning the breaker off and back on

92
Q

A voltage measured across a switch means the switch is:

A

Open

93
Q

When installing add-on split system air conditioning for a residence, you should never:

A

Fish thermostat wires inside EMT along with power wiring

94
Q

In a series circuit, the current:

A

Is the same throughout the series path

95
Q

Jumping a wire across terminals R and G on the subbase of a thermostat will cause the:

A

blower motor to operate

96
Q

A fully hermetic compressor on a 3-ton residential split system has three electrical terminals on the side of the compressor. An ohmmeter reads the following: terminal A to B = 20 ohms, A to C = 15 ohms, and B to C = 5 ohms. There was a reading of infinity between all three terminals to ground. Which terminal is the common terminal?

A

Terminal C

  • Highest reading needs to go through all windings
  • *Next highest reading would be the start tap
  • **The lowest reading is the run tap
  • ***Always check measurements to ground
97
Q

A 3-ton residential split system should move about how many cfm total?

A

1,200 cfm

98
Q

An R-22 air conditioning system is operating with a head pressure of 220 psig and a suction pressure of 68.5 psig. A temperature measurement taken on the suction line 8” from the suction service valve reads 60°F. A temperature measurement taken on the liquid line leaving the condenser reads 90°F. What is the low-side superheat?

A

20°F of superheat

99
Q

A hot wood stove gives up heat to the room by:

A

Conduction
Convection
Radiation

Air-Conditioning Systems (7 decks)

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