DeWalt HVAC Air Conditioning Flashcards
1
Q
The Fahrenheit scale is based on boiling water at sea level at what temperature?
A
212°F
2
Q
Zero pounds gauge corresponds on the absolute scale to:
A
14.7
3
Q
Hidden heat in refrigeration work is referred to as:
A
Latent heat
4
Q
Absolute zero on the Fahrenheit scale is:
A
-459°F
5
Q
A ton of refrigeration is a unit equal to:
A
12,000 BTU per hour
6
Q
The heat used to change a liquid to a gas is called the latent heat of:
A
Vaporization
7
Q
A thermometer is said to “sense” what?
A
Sensible heat
8
Q
Five pounds of water is heated by 2°F. How many Btu were added to the water?
A
10 BTU
9
Q
The amount of heat required to melt 1 pound of ice at 32°F is:
A
144 BTU
10
Q
After all the liquid has been changed to vapor superheat is ____.
A
added
11
Q
Subcooling is ____ added or removed in changing the temperature of a liquid.
A
heat
12
Q
The saturation temperature is the same as the ____ ____ and boiling temperature.
A
condensing temperature
13
Q
Cold is:
A
A relative term with no specific temperature
14
Q
As the pressure over a liquid is lowered:
A
The boiling point of the liquid decreases.
15
Q
As heat is added to a substance:
A
The molecules move faster.
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
17
Q
The specific heat of a substance changes when the:
A
substance changes state.
18
Q
A half-filled cylinder of refrigerant at 80°F will be:
A
Saturated
19
Q
The air you are breathing is:
A
Superheated
20
Q
The three methods of heat transfer are:
A
Conduction, convection, and radiation
21
Q
As a gas is compressed:
A
Temperature and pressure increase.
22
Q
When compressed enough and then cooled, a gas will:
A
Condense
23
Q
The condensing temperature and the _____ temperature mean the same thing.
A
saturation
24
Q
The evaporator is a:
A
Low-pressure component
25
The two components that contain coils are:
Condenser and evaporator
26
Refrigerant vaporizes in the:
Evaporator
27
The two components that divide the high-pressure side from the low-pressure side of a system are the:
Compressor and metering device
28
The pipe that connects the evaporator to the compressor is the:
Suction line
29
The pipe that connects the compressor to the condenser is the:
Discharge line
30
Which one of the following refrigerants would be used with POE oil?
R-410A
31
The discharge line temperature of a reciprocating compressor should never be allowed to exceed how many degrees Fahrenheit?
225°F
32
Refrigerant becomes superheated in the:
Evaporator, suction line, and compressor
33
Refrigerant is in its saturated state in the:
Condenser
34
The temperature-pressure chart works:
Where refrigerant is saturated
35
Which service valve should never be front-seated while the compressor is operating?
Compressor discharge service valve
36
How many microns are there per inch of mercury?
25,400 microns/inch
37
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?
Midseated
38
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?
Fully clockwise
39
A 125-pound cylinder of R-22 is stored in a room at 80°F. The pressure in the cylinder should be:
144 psig
40
Vacuum pressures are measured in:
Both inches of mercury and microns
41
The condenser gives up:
Sensible and latent heat
42
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?
It controls the head pressure during periods of low outside ambient temperatures.
43
A thermostatic expansion valve controls evaporator:
superheat
44
An automatic expansion valve directly controls evaporator:
pressure
45
The oil failure control is operated by the:
oil pump discharge pressure and the suction pressure
46
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:
air filter is restricted and/or the evaporator is dirty.
47
A frosted suction line on an air conditioning application indicates:
The suction line temperature is below the dew point of the ambient air and at or below 32°F.
48
An oversized air conditioning system may cause:
The system to short-cycle
49
Flooded starts on a compressor can be the result of:
Refrigerant migration
Refrigerant overcharge
A burned-out crankcase heater
50
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?
It has a restriction in the liquid line.
51
Low airflow over a residential split system air conditioning evaporator can cause:
Liquid floodback to the compressor
52
As the pressure on a liquid is increased, the vaporization temperature of the liquid:
Increases
53
An oil separator must be mounted:
Level
54
Which metering device controls evaporator pressure?
Automatic Expansion Valve
55
The purpose of the external equalizer on a thermostatic expansion valve (TEV) is to:
equalize evaporator pressure drop with respect to the TEV
56
The higher the MERV rating of a filter-drier, the:
MERV does not apply to filter-driers.
| *They only apply to air filters.
57
Zeolite is used with:
Refrigerant filter-driers
58
Vacuum pressures are measured in:
Microns
Millimeters of mercury
Inches of mercury
59
The number 25,400 relates to:
microns/inch
60
The general rule of thumb for airflow is:
400 cfm/ton
61
A double-suction riser is used to:
Improve oil return as system capacity changes
62
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?
Low on evaporator airflow
63
The normal compression ratio for a typical comfort air conditioning application should be in the range of:
2.75 to 3.75
64
All else being normal, if a system shows a high low-side superheat with high condenser subcooling, what is most likely the problem?
A partial refrigerant restriction
65
All else being normal, if a system shows a low low-side superheat with high condenser subcooling, what is most likely the problem?
Refrigerant overcharge
66
All else being normal, if a system shows a high low-side superheat with low condenser subcooling, what is most likely the problem?
Refrigerant undercharge
67
A grille equipped with a damper control is called a:
register
68
A pressure relief valve is:
Direct pressure acting
69
A parallel compressor system in which both the crankcase oil level and the refrigerant gas pressure are equalized is a(n):
Double pipe crankcase equalizer system
70
In a direct expansion chiller used on air conditioning applications, the refrigerant is on what side of the tubes?
In the tubes
71
The total minimum open area for air to flow through on a supply air register is called the:
Free area
72
Which type of copper tubing has the thickest wall?
Type K
73
What is the gross weight of a refrigerant cylinder?
The weight of the cylinder plus the weight of the refrigerant
74
What does an anemometer measure?
Feet
75
The term “induced draft” most likely refers to a:
type of cooling tower
76
What fitting should be used to connect ¼" copper tubing to a ¼" internal pipe thread opening on a compressor crankcase?
A half union
77
Which of the following compressors has the fewest moving parts?
Rotating vane rotary
Fixed vane rotary
Scroll
Reciprocating
Scroll
78
A hot liquid line with a low to normal high-side pressure is an indication of
An undercharged system
79
Air and water are directed counterflow so as to:
Gain the greatest amount of heat transfer
80
Which of the following applications is not a mechanical cooling system?
Cascade system
Reciprocating compression system
Evaporative cooling
Centrifugal compression system
Evaporative cooling
81
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
Leaking compressor suction valve
82
The position of the valve stem on the suction service valve is normally:
Fully backseated
83
Of the three fundamental fan laws, one states that the power varies by the ______ of the speed.
cube
84
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
Any or all of the above
85
Which of the following compressor oil types is generally considered the most compatible with HFC refrigerants?
POE
AB
Mineral
Vegetable
POE
86
The factor determining the correct quantity of air for each room in a building is the:
calculated heat load for each room
87
Refrigerant 22 is classified as a(n):
A-1 refrigerant
88
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 thermometer, ammeter, and voltmeter
89
A rotating vane anemometer measures:
feet
90
A lockout relay is also called a(n):
Both an impedance relay and a reset relay
91
A lockout relay can be reset by:
De-energizing the main power
Pushing the reset button
Turning the breaker off and back on
92
A voltage measured across a switch means the switch is:
Open
93
When installing add-on split system air conditioning for a residence, you should never:
Fish thermostat wires inside EMT along with power wiring
94
In a series circuit, the current:
Is the same throughout the series path
95
Jumping a wire across terminals R and G on the subbase of a thermostat will cause the:
blower motor to operate
96
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?
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
A 3-ton residential split system should move about how many cfm total?
1,200 cfm
98
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?
20°F of superheat
99
A hot wood stove gives up heat to the room by:
Conduction
Convection
Radiation
