Quiz Questions Flashcards
1
Q
When a heat pump is operating in defrost mode, outdoor fan…
A
Is off
2
Q
The amount of moisture in the air compared to the amount of moisture the air can hold at the temperature
A
Relative Humidity
3
Q
Where will the refrigerant be superheated at the..
A
Outlet of compressor, inlet of the condenser, the outlet of the evaporator
4
Q
R-410a cylinder colour
A
Rose
5
Q
Pure water boils at 212F at what pressure?
A
14.7 psia
6
Q
Refrigerant with low toxicity and no flame propagation is classifaction
A
A1
7
Q
A substance that changes from the solid to the vapour state without going through liquid state. Is called
A
Sublimation
8
Q
The amount of heat required to raise one pound of water, one degree Fahrenheit
A
Btu
9
Q
Technician removes refrigerant from a system and stores it in an approved cylinder, this is
A
Recovery
10
Q
Absolute Fahrenheit scale is called the
A
Rankin scale
11
Q
What locations is does the saturated pressure correspond to the saturated temperature
A
Evaporator and condenser
12
Q
If refrigerant has a quality of 75% it is
A
75% liquid 25% vapor
13
Q
Latent heat of vaporization is
A
The amount of heat required to change liquid to vapour
14
Q
Refrigerant vapour entering the metering device can be caused by
A
A restriction in liquid line, a dirty condenser coil, and undercharged system or leak
15
Q
Fresh air brought into a house for ventilation purposes is usually
A
Connected to the return of duct system
16
Q
Suction pressure being low can be caused by
A
Dirty condenser coil, low charge, low ambient air temp, dirty filter
17
Q
Refrigerant leaving the condenser will be
(3)
A
Subcooled, liquid, high pressure
18
Q
At a constant pressure the volume of gas varies directly at to absoloute temp and at a constant volume, the pressure of a gas varies directly with absoloute temp
This is called:
A
Charles law
19
Q
System equipped with fixed orfice metering device has a sudden increase of indoor temp, what will be the effect on superheat if outdoor conditions remain the same
A
Superheat will increase
20
Q
Technician found the the evaporator is operating at a very high superheat, they determined the metering device is ______the evaporator
A
Starving
21
Q
410a is a near azeotropic blend, you should charge the system…
A
In liquid state through suction valve
22
Q
A frosted suction line indicates
A
The suction line temp is below dee point if the ambient air or below 32F
23
Q
Describe refrigeration
A
The process of removing heat from a place it is not wanted and transferring that heat to a place where it makes little or no difference
24
Q
The liquid and vapour mixture in the condenser is a
A
Saturated temperature for the high side of the system
25
The total pressure if a confined mixture of gases is the sum of the pressure of each of the gases in the mixture
Dalton’s law
26
Water has a density of 62.4 lbs/cu ft. What’s it’s specific gravity
1
27
The term hygroscopic refers to
Moisture absorbing abilities of a substance
28
The refrigerant absorbs heat in the
Evaporator and compressor
29
Temp of gas leaving the compressor
Hot
30
Like txv, fixed orfice device controls superheat by losing the refrigerant pressure
Fixed orfice does not control superheat
31
Presssure in a refrigeration system is changed in the
Compressor and metering device
32
High temp refrigeration is an
AC System
33
The heat of compression that is generated in the compressor is removed from the refrigerant in the
Condenser
34
The capacity of a 2.5 ton ac system is
30,000 btu
(12,000 x 2.5)
35
What is the movement of heat through space called
Radiation
36
Heat transfer though space is called
Radiation
37
An external equalizer line on a txv is designed to
Compensate for pressure drop
38
As refrigerant passes through the metering device, the result is a drop in pressure and temp, with no change in heat content. This is known as
Adiabatic expansion
39
The amount of heat required to change the temp of one pound of a substance by one degree Fahrenheit
This is know as
Specific heat
40
What minimizes migration of refrigerant to compressor
Crank case heater
41
Removing heat from liquid refrigerant, below it’s condensing temp
Subcooling
42
Static pressure in a full oxygen cylinder is
2000
43
29” Hg. Vac is equal to
0.46 psia
44
What symptoms would an ac system exhibit if the condenser coil is dirty
High head pressure, low subcooling
45
Refrigerant flow into evaporator with a fixed orfice metering device is controlled by
Pressure different between condenser and evaporator
46
The ozone layer found in the stratosphere is made up of
3 oxygen atoms
47
Split systems installed with excessive liquid line length and lift, it could case
Flash gas in the liquid line
48
Cu ft/ lb is…
Specific volume
49
The volume of gas varies inversely with absolute pressure, provided the temp is constant
What law is this?
Boyle law
50
External equalizer line should be installed
Downstream of bulb
51
Evaporator coils for ac are designed to have
(CFM)
350-400 CFM per TON
52
System designed to have 11F of subcooling this is important to
Prevent vapour from entering metering device
53
When ordering 7/8” copper tubing the 7/8” refers to the
Outside diameter
54
Red gauge also know as
Pressure gauge
55
Proper subcooling is normally an indication of
A properly charged system
56
A blend of 2 refrigerants that have similar boiling points and do not separate liquid or vapour state is known as
Azeotropic blends
57
Most residential condensing unit compressor are cooled by
Refrigerant
58
The temp above which vapour cannot be condensed regardless of the pressure placed upon it is known as
Critical temp (point)
59
A heat pump the uses reciprocating compressor should be equipped with what device to protect it from possible liquid flood back
Accumulator
60
What should a pump down system have
A receiver
61
During operation, the suction line should be
Slightly warmer then the evaporator saturation temp
62
The temp of the air leaving the condenser is______ then ambient air
Warmer
63
Amount of air flow per ton is required through the evaporator of an ac system is
400CFM
64
What not to pressure test with
Oxygen and compressed air
65
Technician wants to determine amount of sensible heat added to refrigerant above saturation point in the evaporator coil, they would
Perform a superheat check on suction line
66
A bourdon tube is often found in a
Pressure gauge
67
Technician has determined that a newly installed refrigeration system is leaking free, before charging the system with refrigerant they must
Evacuate system
68
Evaporator T.D is the difference between
Air temp entering the evaporator and saturated suction temp
69
Which valve is a mechanical control the keeps the refrigerant in evaporator from going bellow a predetermined point
EPR Valve
Evaporator pressure regulator
70
The bulb for txv should be located
On the suction line at the outlet of the evaporator
71
When installing a resi split system, the ______ line should be insulated
Suction
72
What meter uses its own power source
Ohmmeter
73
When defrost cycle is terminated, the evaporator fans will
Delay coming on
74
Natural refrigerants are
(3)
Ammonia, carbon dioxide and hydrocarbon(propane)
75
Only vapour is present, it is
Superheated
76
Only liquid is present, it is
Subcooled
77
More net refrigeration=
More cooling
78
Bubble point on the
Liquid side
79
Dew points on the
Vapour side
80
Refrigerant will always travel to the
Coldest part
81
1KW=______btu
3412
3.412 x1000
82
1HP=______btu/h
2545
3.412 x 745
83
1W=______btuh
3.412
84
Dentsity=
Mass- volume ratio(lbs/ft3)
1/specific volume
85
Volume of 1 pound of gas (ft3/lb)
Specific volume
86
1 ton of refrigerant per minute
200 Btu/min
87
1 ton refrigerant per hour
12000 Btu/hr
88
Low subcooling and high superheat means the systems
Undercharged
89
Backseat means
Valve is closed
90
Valve is ________ for pump down
Frontseated
91
Valves mid seated for
Standing pressure test and evacuation
92
As compression ratio of compressor is increased due to higher than normal head pressure
Less refrigerant is pumped though system
93
Refrigerant muffler is installed on the
Discharge line
94
What valve design helps to increase compressor efficiency by reducing clearance volume
Discus valve
95
Most hermetic motor windings are cooled by
Cool suction gas
96
A de-superheating valve in a hot gas bypass capacity control system is designed to
Mia some liquid with the hot gas to cool it down
97
Changed the pitch and diameter of a pulley will not effect amp draw
T/F
False
98
As the piston moved down in the cylinder of a reciprocating compressor
Suction valve will open, moves towards BDC, and re-expansion will occur
99
One form of capacity control to prevent gas from entering the cylinder chamber is
Cylinder unloading
100
What’s better scroll or reciprocating compressor and why
Scroll, no volumetric loaded from gas re-expansion
101
As piston moves up in reciprocating comp cylinder
Volume is decreased, pressure is increased
102
What conditions can lead to higher than normal compression ratios
Dirty condenser, low suction pressure, high discharge pressure
103
When piston of reciprocating compressor at TDC, but suction and discharge valve are….
Closed
104
Starting at TDC position, the 4 processes that occur in the cylinder of a reciprocating compressor are
Re-expansion, suction, compression, discharge
105
Clearance volume for reciprocating compressor
Decreases volumetric efficiency
106
A compressor which is driven by a variable frequency drive
Can change speed of the compressor
107
Best location to measure discharge temp to ensure compressor isn’t running too hot
6” from discharge valve (downstream)
108
Flapper or reed valves are used in the
Reciprocating compressor
109
Capacity control method unique to scroll compressor
2 stage modulation by using bypass ports to reduce capacity to approximately 67%
110
What is volumetric efficiency
How well compressors operating compared to theoretical design capacity
111
Shell and tube type evaporator that has refrigerant passing though the tubs and the shell is full of water is known as
Direct expansion or dry type
112
Refrigerant leaves metering device as
Saturated mixture of vapour and liquid
113
Density of air is the
Weight of air per unit of volume
114
To process refrigerant to new product specifications “off cite”
Reclaiming
115
What does the condenser do
De-superheats the vapour, condenses the valour, Subcools liquid refrigerant before it leaves the condenser,
116
Refrigerant entering the evaporator is
Low pressure, cold, saturated
117
Evaporator TD is the difference between
Air temp entering the evaporator and saturated suction temperature
118
Enters the compressor as____
Leaves as______
Low pressure, low temperature, superheated
High pressure, high temperature, superheated vapour
119
Fahrenheit scale where molecular activity stops
-460 F
120
If temperatures constant, volume of gas increased the pressure will…
Decrease
121
Suction line pressure and temperature determine
Superheat leaving evaporator
122
Subcooling important because…
Increases system capacity
123
Tube-within-tube water cooled condenser operated more efficiently with counter flow, which means..
Refrigerant is flowing through in one direction and water in the other
124
Condenser split refers to
Temperature of air entering coil compared to the saturated condensing temperature
125
Functions of condenser
De-superheat discharge vapour from compressor, condense refrigerant to liquid, reject heat from system and subcool liquid refrigerant
126
Shell and tube condenser is..
Water flows through tubes and are surround by refrigerant in the shell
127
As water flows through water cooled condensers
Temperature increases
128
Condenser operates at______ than evaporator
Higher pressure
129
Condenser rejects
Sensible and latent heat
130
As refrigerant passes through the condenser is
Gives up heat
131
Shell and tube condensers must be cleaned
With brush after removing end caps
132
Varied temperature of wastewater type condenser has an effect on the
Head pressure of condenser
133
Shell and coil condenser must be cleaned
Chemically
134
Tube within tube condenser is______ cooler
Water cooled
135
Refrigerant entering condenser is
Superheated
136
Air is made up of
78% nitrogen, 21% oxygen, 1% other gases
137
Comfort enquires
Temperature, humidity, air movement, air cleanliness
138
Human body runs at about
98.6 F
139
Density is
Mass of substance per unit of volume lb/ft3
140
Dry air weighs
0.75 lbs/ft3
141
Dew point temp is
Temperature which water will begin to condense out of the air
142
Specific humidity is
Actual amount of moisture in air measured in grains of moisture per pounds of air
143
Approximate amount of grains of moisture per pound of water
7000 grains
144
How many cubic feet of air equal to one pound
1/0.075 lbs/ft3= 13.33 lbs/ft3
145
The spring of a txv is a
Closing force
146
Automatic expansion valve
Meters refrigerant to evaporator by using a pressure sensing device
Maintains constant pressure in evaporator
147
When does the AEV valve open
When pressure drops
148
How to adjust AEC
Clockwise to open
Turning screw into valve increases suction pressure
149
Capillary tube metering device
Controls refrigerant flow by pressure drop
Diameter and length determine flow
Doesn’t control superheat
150
Orfice/ piston metering device
Similar to capillary
151
Txv and atv need
Receiver
152
Capillary tubes are charged
Critically
153
Bulb pressure _____ valve
Opens
154
Evaporator pressure______valve
Opens
155
What does the 4 way reversing valve do
Allows heat pump to pump heat in 2 directions
156
For way reversing valve function in heating cycle
Discharge gas is directed from compressor to indoor coil (condenser)
157
Larger line on heat pump system is called
And functions as
Gas line
Suction line in cooling
Discharge in heating
158
Smaller line on heat pump is called
And liquid flows
Liquid line
To inside unit in summer
To outside unit on winter
159
Four port valve with slide mechanism for larger systems
Use pilot operated valve that use high side pressure to push slide
160
Air to air heat pump resembles
Mode determined by
AC System
Direction of flow
161
Auxiliary heat required when
Heat pump can’t provide all the heat needed
162
Balence point is
When heat pump is can pump in exactly as much heat as structure leaking out
163
Air to air heat pump COP IS
3.5:1
164
Air to water COP
4:1
165
for way reversing valve has
2 inlets 2 outlets
166
Air source heat pump has
2 metering devices
167
In heating mode, heat pumps gain efficiency as outdoor ambient temp drops
T/F
False
168
Electric auxiliary heaters for a heat pump are turned on in stages using
Heat sequencers
169
Defrost mode for air sources heat pump can be initiated by…
Pressure differential, temperature, time
170
Outdoor coil operates at the_____ in the heating cycle
Evaporator
171
Filter dryers installed in heat pump system should be of the byflow type or installed with…
Check valves
172
Metering devices for most heat pumps are piped in parallel with
The check valves (bypass valve)
173
Indoor coil of a heat pump operates as the_____ in the heating cycle
Condenser
174
Defrost cycle in heat pump is used to melt the ice that forms on the
Outdoor coil
175
During defrost, the indoor fan is turned off
T/F
False
176
Heat pump that absorbs heat from surrounding air and rejects it into are in a different place is an…
Air to air
177
EEV constantly monitoring superheat based on…
Pressure transducer and temperature sensor
178
Capacity control for reciprocating compressor can be achieved by using
Unloaders
179
Micron gauge should be…
Furthest point away from vacuum pump
180
As compression ratio increase, the volumetric efficiency…
Decreases
181
The suction valve of a reciprocating compressor opens based on
Pressure differential
182
Efficiency of reciprocating compressor can reduce due to
Re-expansion of refrigerant in cylinder
183
Advantage of open drive compressor is…
Motor can be replaced without recovering the refrigerant
184
The top scroll in a scroll compressor is
Stationary
185
Digital scroll compressor achieves capacity by..
Momentarily separating the orbiting scroll from the fixed scroll
186
Suction gas contaminated heat absorbed while it’s in the..
Evaporator
187
Rotary compressor requires..
2 full rotations to complete 1 compression process
188
The temperature of suction gas entering the compressor can be described as.
Cool
189
Clearance volume is..
The space between to top of the piston at TDC and the bottom of the valve plate
190
Discus style reciprocating compressor design helps to eliminate the re-expansion of gas in cylinder changer
T/F
True
191
Discus valve is more efficient than reed valve because..
Allows the cylinders to be designed with less clearance volume
192
Most heat absorbed by suction gas…
Latent
193
If compressor discharge is too high it will lead too
The oil breaking down and lead to compressor failure
194
Air conditioning is considered to be a________ refrigeration
High temp
195
No superheat can cause_____ in the evaporator
Flooding
196
High superheat can cause _____ in the evaporator
Starving
197
How many classes of leaks are there?
6
198
In refrigerant classification chart the higher the number, the higher…
Flammability
199
I’m the refrigeration classification chart, the B section means…
Higher toxicity
200
Can you vapour charge with 410a
No, it will fractionate
Because it’s a blended refrigerant
201
Can you vapour charge R22
Yes.
Because it’s a single component
202
Can you use a torch to warm up a refrigerant cylinder
No
203
Blended compound refrigerant series are…
400 and 500 series
204
Liquid refrigerant can be added through the..
Liquid line or receiver
205
When charging with blended refrigerant the refrigerant must leave the cylinder as a…
Liquid
206
Superheat method of charging is used for
Fixed orfice or capillary tube
207
To charge a heat pump it should be set in
Cooling mode
208
Subcooling charging method is used for
TXV
209
Heat pump is more efficient in what mode
Heating mode
210
Dew point and bubble point are for _____ refrigerants
Zeoptropic
211
400 series are
Zeotropic
212
500 series are
Azeotropic
213
Fractionation is
Part of the blend will epaporate or condense before the other part
214
What type of oil absorbs moisture
POE
215
High td means
Low humidity
216
Four way reversing
Top is:
Bottom middle:
Top: always permanent discharge
Bottom middle: always permanent suction
217
What causes
Head pressure will go down
Suction will go up
Compression ratio will decrease
Four way reversing valve is leaking
218
A four way reversing valve with an internal leak can be confused with
Be confused with a compressor not pumping to capacity
219
Loose bulb leads to
High suction heat (feeling more heat)
220
Psig of acetalyn tank is
250 psig
221
Psig of nitrogen is
2200 Psig
222
Psig of oxygen tank is
2000 Psig
223
A before O and off you go
Acetylene, then Oxygen
224
Difference between tube and pipe
Pipes-measured inside diameter (black pipe)
Tube-measured outside diameter (copper)
225
Pressure(Psig) for torch would be same as
Tip size
226
Liquid condensate line connects
Condenser to receiver
227
Velocity is
Ft/min (fpm)
228
Pipe diameter increases the velocity
Decreases
Visa versa
229
Temperature is an indication of the:
Amount of molecular activity in the material
230
When heat transfers by convention, it
Is transported from one place to another by air or liquid
231
The temperature in the Celsius scale where all molecular activity stops is:
-273C
232
When a vapour no longer corresponds to to pressure/ temperature relationship, it is known as_____vapour
Superheated
233
As refrigerant passes through the metering device, the result is a drop in pressure and temperature, with no change in heat content
This is known as:
Adiabatic expansion
234
While inspecting an AC system, a tech finds the head pressure running significantly higher than normal for the current outdoor temp. They also notice that the liquid line temp and the outdoor temp are the same.
What could be the cause?
System is overcharged
235
R-value represents
An insulations resistance to heat transfer
236
As the temperature of a material increases, the molecules in the material
Increase in speed
237
134a, Vapour enters the condenser at 124psig and 100F, it leaves the condenser at 80F what’s the pressure?
124psig
238
The role of the metering device in a heat pump is to
Meter refrigerant
239
If the sensing bulb in txv developed a leak and started to loose charge, the result would be
The evaporator would be starved and superheat would be high
240
If a system has a restriction in the metering device, a technician should expect:
High superheat and normal subcooling
241
When the refrigerant enters the evaporator, it is:
At low pressure, cold and saturated
242
The blue gauge is know as
A compound gauge
243
Many rating for components in HVAC systems are not completely accurate due to many different operating conditions are called:
Nominal
244
When do potential relays close
Loss of counter EMF
