Hvac Unit 1 Flashcards
(145 cards)
1
Q
A btu is defined as?
A
Amount of heat to raise the temp of 1lb of water 1°F
2
Q
Evaporation is defined as?
A
Change state from liquid to vapor absorbing heat
3
Q
Condensing is defined as?
A
Change of state from vapor to liquid rejecting heat
4
Q
Sensible heat defined as?
A
A change of temp without a change in state
5
Q
Latent heat defined as?
A
A change in state without a change of temp
6
Q
When temp goes up…
A
Pressure and saturation goes up
7
Q
When temp goes down…
A
Pressure and saturation goes down
8
Q
Best definition of Saturation?
A
PSIG converted to temp
9
Q
Define superheat
A
Sensible heat added to a vapor above its saturation point
10
Q
Formula for Superheat?
A
(Slt) Actual suction line temp - (Vsat) suction saturation temp = superheat / vapor
11
Q
High superheat means?
A
Starved evaporator
12
Q
Low superheat means?
A
Flooded evaporator
13
Q
Formula for subcooling
A
(Lsat) Liquid saturation temp - (Llt) actual liquid line temp = subcooling / liquid
14
Q
Subcooling is defined as?
A
Sensible heat removed from a liquid below its saturation point
15
Q
High subcooling means?
A
Flooded Condenser
16
Q
Low subcooling means?
A
Starved condenser
17
Q
What is the color for superheat?
A
Blue
18
Q
What is the color for subcooling?
A
Red
19
Q
How do we find the target superheat for a fixed orifice?
A
All of the above = chart, app, formula
20
Q
What is our general target for T.X.V.?
A
8-14
21
Q
Which metering device focuses on subcooling?
A
T.X.V.
22
Q
You have high superheat and low subcooling what is wrong?
A
Starved, Undercharged/find and repair leak/needs refrigerant
23
Q
You have low superheat and high subcooling
A
Overcharged, flooded, recover
24
Q
T.X.V. low superheat low subcooling
A
Indoor flooded, outdoor starved, txv stuck open, sensing bulb detached
25
T.E.V. superheat good subcooling high
Evap good, con flooded, recover
26
Louis Carrier made AC to do what?
Dehumidify and cool
27
John Gorrie invented what?
Ice machine
28
1st law of thermodynamics?
Energy cannot be created nor destroyed only transformed or transferred
29
2nd law of thermodynamics?
Heat seeks cold
30
3 things that affect 2nd law of thermodynamics?
Conductivity, surface area, temp difference
31
Refrigeration is defined as?
Moving heat that is unwanted to a place that is insignificant
32
Define recovery?
Moving refrigerant from a unit in any condition and putting it into a recovery tank
33
To add a refrigerant to a system...
Throttle it to the low side
34
To recover a refrigerant the system is running?
Recover refrigerant to the high side
35
When do you recover?
When it's overcharged, or open for repair
36
Old refrigerant we don't use
R22 green
37
Current refrigerant we use
R410A rose
38
Where does used refrigerant go?
Recovery tank
39
True or false: Sensible heat is more powerful than latent heat
False
40
Color of recovery tank
Gray body with yellow top
41
An AC will freeze because...
Saturation temp is below 32°F
42
#1 reason AC will freeze
Poor/bad airflow
43
Examples why AC freezes
Restriction, Leak, Low outdoor temp = All of the above
44
Three ways heat travels
Conduction, convection, radiation
45
Warm air rising is an example of what?
Convection
46
Heat from the sun is?
Radiation
47
Heat through touch is?
Conduction
48
What is the state of vapor coming from compressor?
High pressure highly superheated vapor
49
3 steps refrigerant goes through condenser?
Desuperheat, Condense, Subcools
50
What is the state of a refrigerant entering metering device?
High pressure high temp subcool liquid
51
State of refrigerant leaving metering device?
Low pressure low temp saturation
52
What is the state of refrigerant entering compressor?
Low pressure low temp superheated vapor
53
Accessory installed between condenser and metering device?
Liquid line filter drier
54
14.7 PSIA is
0 PSIG
55
Why do we want superheat entering compressor?
Prevents liquid to go to compressor
56
What does the temp difference across the filter drier mean?
Restricted filter drier
57
What does a partially clogged Fixed Orifice cause?
Starved evaporator
58
Refrigerant enters the evaporator as...
Liquid with some flash gas
59
How many BTUs in a 1 ton?
12000 BTUs
60
How many BTUs in 2 tons of refrigerant?
24000 BTUs
61
How many BTUs in 3 tons of refrigerant?
36000 BTUs
62
How many BTUs in 5 tons of refrigerant?
60000 BTUs
63
What happens to the high and low psi when the evap coil is restricted?
They go down
64
The evaporator does?
Absorbs heat changes refrigerant from saturation to vapor
65
The condenser does?
Rejects heat, changes refrigerant from vapor to liquid
66
Higher altitudes does?
Water boils at lower temp
67
Lower altitudes does?
Water boils at higher temp
68
80°F of superheat most likely means?
Starved evaporator
69
80°F of subcooling most likely means?
Flooded condenser
70
-5°F of superheat most likely means?
Flooded evap
71
-5°F of subcool most likely means?
Starved condenser
72
Where does Sat start at the Evap?
At the metering device
73
Where does Sat take place in Con?
The center/middle
74
When outdoor temp goes up what happens to pressures?
They go up
75
A recovery tank has 10lbs of R410A; it's been sitting at 70°F for 8 hrs. What's the PSIG?
Check Chart. 201 PSIG
76
A recovery tank has 5lbs of R410A; it's been sitting at 70°F for 8 hrs. What's the PSIG?
Check Chart. 201 PSIG
77
What is the difference between deltaT and TD?
DeltaT=same media. TD=different media
78
Whats the DeltaT? R/A: 78°F S/A:55°F
DeltaT: 23°F
79
What is return air?
Air returning to the evaporator
80
What is the supply air?
Air supplied to the structure
81
How do you properly size AC?
Manual J or Wrightsoft
82
Which metering device focuses on superheat?
F.O.
83
What happens to superheat and subcool when the sensing bulb is closed?
SH=Increase Starved SC=Increase Flooded
84
What happens if superheat and subcool if sensing bulb is detached?
Both are low E=Flooded Con=Starved
85
Symptoms of oversized fixed orifice for superheat and subcool?
Low for both E=Flooded C=Starved
86
Symptoms of undersized fixed orifice for superheat and subcool?
High for both E=Starved C=Flooded
87
You increase indoor blower speed how would that affect DeltaT? R/A-S/A=DeltaT
DeltaT goes down
88
Where is the filter drier located? Where is the arrow pointed?
Liquid line arrow directed to evaporator
89
What is true cold?
O°K
90
Which one is the suction line? Which one is the liquid line?
SL is bigger low pressure LL is smaller high pressure
91
Symbol for resistive load
-/\/\-
92
Symbol for inductive load
-uuu-
93
Open Switch
-| |-
94
Closed Switch
-N-
95
Xfmr means
Transformer
–| |–
3 | | 3
3 | | 3
3 | | 3
–| |–
96
Ohms law
E
----
I | R
97
Switches are
Wired in series to loads and are passing devices
98
Loads are
Wired in parallel and power consuming devices
99
Which component is a switch and load
Contactor
100
Inductive load
Solenoid
101
Resistive load
Heating element
102
Amps =
I
103
Ohms =
R
104
Volts =
E
105
Another word for amps
Currents
106
Amps means
Rate of electron flow/current
107
How do you check for amps
Amp clamp around single wire w/power
108
Voltage means
Potential difference
Electromotive force
Force of electrons
All the above
109
How do you check for voltage
Meter leads across two points
110
Symbol for ohms
Horseshoe
111
Ohms mean
Resistance to electron flow
112
How to check ohms
Isolate component
Meter leads across two points
113
When do you use ohms on alive current
Never
114
Set resistance = stays the same
Voltage increases
115
Amps to wattage
They increase
116
Same as 65 but decreases
They decrease
117
Formula for watts
W = v × a
118
Circuit must have
Source, path, load
119
0 Ohms means
0 resistance/free flow
120
OL means
Infinite resistance
121
0 Ohms across a switch
Switch closed
122
OL Ohms across a switch
Open switch
123
Loads will have
Some # of Ohms/Resistance
124
Thermostat calls for fan, what connects
R-G
125
Cool, always connect
R-Y
126
Heat, always connect
R-W
## Footnote
R= 24v power/source
Y=Compressor contactor
G= Indoor Fan relay
W= Indoor Heat
C= Low voltage home/Common
127
1st step to diagnose an AC
Turn thermostat on
128
Primary side of XFMR is
High Voltage
129
Secondary side of XFMR is
Low Voltage
130
Low side of XFMR should have a
Fuse
131
How do you do a safety check
Check from
Line 1 to line 2
Line 1 to ground
Line 2 to ground
132
#1 cause of electrical failures
Loose wires
133
A fuse or breaker trips because
Overamping & a short
134
24v to CC coil is not closing, what's wrong
Bad contactor
135
0v to CC coil is not closing, what's wrong
Contactors not bad find where 24v volts is last
136
24v to CC coil is closing, what's wrong
Contactor is doing its job
137
Fan is on vac between R and G
0v
138
Fan is on R & W
24v
139
FR checking VAC across a NC w/o coil energized
0v
140
FR checking VAC across a NO w/o coil energized
Source volts
141
FR checking VAC across a NC with coil energized
Source volts
142
FR checking VAC across a NO with coil energized
0v
143
Component that controls many heating elements
Heat sequencers
144
What turns on when contactor runs
Compressor & condenser fan motor
145
Overcurrent protection device
Circuit breaking
