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Hvac Unit 1 Flashcards

1
Q

A btu is defined as?

A

Amount of heat to raise the temp of 1lb of water 1°F

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2
Q

Evaporation is defined as?

A

Change state from liquid to vapor absorbing heat

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3
Q

Condensing is defined as?

A

Change of state from vapor to liquid rejecting heat

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4
Q

Sensible heat defined as?

A

A change of temp without a change in state

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5
Q

Latent heat defined as?

A

A change in state without a change of temp

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6
Q

When temp goes up…

A

Pressure and saturation goes up

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7
Q

When temp goes down…

A

Pressure and saturation goes down

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8
Q

Best definition of Saturation?

A

PSIG converted to temp

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9
Q

Define superheat

A

Sensible heat added to a vapor above its saturation point

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10
Q

Formula for Superheat?

A

(Slt) Actual suction line temp - (Vsat) suction saturation temp = superheat / vapor

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11
Q

High superheat means?

A

Starved evaporator

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12
Q

Low superheat means?

A

Flooded evaporator

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13
Q

Formula for subcooling

A

(Lsat) Liquid saturation temp - (Llt) actual liquid line temp = subcooling / liquid

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14
Q

Subcooling is defined as?

A

Sensible heat removed from a liquid below its saturation point

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15
Q

High subcooling means?

A

Flooded Condenser

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16
Q

Low subcooling means?

A

Starved condenser

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17
Q

What is the color for superheat?

A

Blue

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18
Q

What is the color for subcooling?

A

Red

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19
Q

How do we find the target superheat for a fixed orifice?

A

All of the above = chart, app, formula

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20
Q

What is our general target for T.X.V.?

A

8-14

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21
Q

Which metering device focuses on subcooling?

A

T.X.V.

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22
Q

You have high superheat and low subcooling what is wrong?

A

Starved, Undercharged/find and repair leak/needs refrigerant

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23
Q

You have low superheat and high subcooling

A

Overcharged, flooded, recover

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24
Q

T.X.V. low superheat low subcooling

A

Indoor flooded, outdoor starved, txv stuck open, sensing bulb detached

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25
Q

T.E.V. superheat good subcooling high

A

Evap good, con flooded, recover

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26
Q

Louis Carrier made AC to do what?

A

Dehumidify and cool

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27
Q

John Gorrie invented what?

A

Ice machine

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28
Q

1st law of thermodynamics?

A

Energy cannot be created nor destroyed only transformed or transferred

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29
Q

2nd law of thermodynamics?

A

Heat seeks cold

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30
Q

3 things that affect 2nd law of thermodynamics?

A

Conductivity, surface area, temp difference

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31
Q

Refrigeration is defined as?

A

Moving heat that is unwanted to a place that is insignificant

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32
Q

Define recovery?

A

Moving refrigerant from a unit in any condition and putting it into a recovery tank

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33
Q

To add a refrigerant to a system…

A

Throttle it to the low side

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34
Q

To recover a refrigerant the system is running?

A

Recover refrigerant to the high side

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35
Q

When do you recover?

A

When it’s overcharged, or open for repair

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36
Q

Old refrigerant we don’t use

A

R22 green

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37
Q

Current refrigerant we use

A

R410A rose

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38
Q

Where does used refrigerant go?

A

Recovery tank

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39
Q

True or false: Sensible heat is more powerful than latent heat

A

False

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40
Q

Color of recovery tank

A

Gray body with yellow top

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41
Q

An AC will freeze because…

A

Saturation temp is below 32°F

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42
Q

1 reason AC will freeze

A

Poor/bad airflow

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43
Q

Examples why AC freezes

A

Restriction, Leak, Low outdoor temp = All of the above

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44
Q

Three ways heat travels

A

Conduction, convection, radiation

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45
Q

Warm air rising is an example of what?

A

Convection

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46
Q

Heat from the sun is?

A

Radiation

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47
Q

Heat through touch is?

A

Conduction

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48
Q

What is the state of vapor coming from compressor?

A

High pressure highly superheated vapor

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49
Q

3 steps refrigerant goes through condenser?

A

Desuperheat, Condense, Subcools

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50
Q

What is the state of a refrigerant entering metering device?

A

High pressure high temp subcool liquid

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51
Q

State of refrigerant leaving metering device?

A

Low pressure low temp saturation

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52
Q

What is the state of refrigerant entering compressor?

A

Low pressure low temp superheated vapor

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53
Q

Accessory installed between condenser and metering device?

A

Liquid line filter drier

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54
Q

14.7 PSIA is

A

0 PSIG

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55
Q

Why do we want superheat entering compressor?

A

Prevents liquid to go to compressor

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56
Q

What does the temp difference across the filter drier mean?

A

Restricted filter drier

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57
Q

What does a partially clogged Fixed Orifice cause?

A

Starved evaporator

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58
Q

Refrigerant enters the evaporator as…

A

Liquid with some flash gas

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59
Q

How many BTUs in a 1 ton?

A

12000 BTUs

60
Q

How many BTUs in 2 tons of refrigerant?

A

24000 BTUs

61
Q

How many BTUs in 3 tons of refrigerant?

A

36000 BTUs

62
Q

How many BTUs in 5 tons of refrigerant?

A

60000 BTUs

63
Q

What happens to the high and low psi when the evap coil is restricted?

A

They go down

64
Q

The evaporator does?

A

Absorbs heat changes refrigerant from saturation to vapor

65
Q

The condenser does?

A

Rejects heat, changes refrigerant from vapor to liquid

66
Q

Higher altitudes does?

A

Water boils at lower temp

67
Q

Lower altitudes does?

A

Water boils at higher temp

68
Q

80°F of superheat most likely means?

A

Starved evaporator

69
Q

80°F of subcooling most likely means?

A

Flooded condenser

70
Q

-5°F of superheat most likely means?

A

Flooded evap

71
Q

-5°F of subcool most likely means?

A

Starved condenser

72
Q

Where does Sat start at the Evap?

A

At the metering device

73
Q

Where does Sat take place in Con?

A

The center/middle

74
Q

When outdoor temp goes up what happens to pressures?

A

They go up

75
Q

A recovery tank has 10lbs of R410A; it’s been sitting at 70°F for 8 hrs. What’s the PSIG?

A

Check Chart. 201 PSIG

76
Q

A recovery tank has 5lbs of R410A; it’s been sitting at 70°F for 8 hrs. What’s the PSIG?

A

Check Chart. 201 PSIG

77
Q

What is the difference between deltaT and TD?

A

DeltaT=same media. TD=different media

78
Q

Whats the DeltaT? R/A: 78°F S/A:55°F

A

DeltaT: 23°F

79
Q

What is return air?

A

Air returning to the evaporator

80
Q

What is the supply air?

A

Air supplied to the structure

81
Q

How do you properly size AC?

A

Manual J or Wrightsoft

82
Q

Which metering device focuses on superheat?

83
Q

What happens to superheat and subcool when the sensing bulb is closed?

A

SH=Increase Starved SC=Increase Flooded

84
Q

What happens if superheat and subcool if sensing bulb is detached?

A

Both are low E=Flooded Con=Starved

85
Q

Symptoms of oversized fixed orifice for superheat and subcool?

A

Low for both E=Flooded C=Starved

86
Q

Symptoms of undersized fixed orifice for superheat and subcool?

A

High for both E=Starved C=Flooded

87
Q

You increase indoor blower speed how would that affect DeltaT? R/A-S/A=DeltaT

A

DeltaT goes down

88
Q

Where is the filter drier located? Where is the arrow pointed?

A

Liquid line arrow directed to evaporator

89
Q

What is true cold?

90
Q

Which one is the suction line? Which one is the liquid line?

A

SL is bigger low pressure LL is smaller high pressure

91
Q

Symbol for resistive load

92
Q

Symbol for inductive load

93
Q

Open Switch

94
Q

Closed Switch

95
Q

Xfmr means

A

Transformer
–| |–
3 | | 3
3 | | 3
3 | | 3
–| |–

96
Q

Ohms law

A

E
—-
I | R

97
Q

Switches are

A

Wired in series to loads and are passing devices

98
Q

Loads are

A

Wired in parallel and power consuming devices

99
Q

Which component is a switch and load

100
Q

Inductive load

101
Q

Resistive load

A

Heating element

102
Q

Amps =

103
Q

Ohms =

104
Q

Volts =

105
Q

Another word for amps

106
Q

Amps means

A

Rate of electron flow/current

107
Q

How do you check for amps

A

Amp clamp around single wire w/power

108
Q

Voltage means

A

Potential difference
Electromotive force
Force of electrons
All the above

109
Q

How do you check for voltage

A

Meter leads across two points

110
Q

Symbol for ohms

111
Q

Ohms mean

A

Resistance to electron flow

112
Q

How to check ohms

A

Isolate component
Meter leads across two points

113
Q

When do you use ohms on alive current

114
Q

Set resistance = stays the same

A

Voltage increases

115
Q

Amps to wattage

A

They increase

116
Q

Same as 65 but decreases

A

They decrease

117
Q

Formula for watts

A

W = v × a

118
Q

Circuit must have

A

Source, path, load

119
Q

0 Ohms means

A

0 resistance/free flow

120
Q

OL means

A

Infinite resistance

121
Q

0 Ohms across a switch

A

Switch closed

122
Q

OL Ohms across a switch

A

Open switch

123
Q

Loads will have

A

Some # of Ohms/Resistance

124
Q

Thermostat calls for fan, what connects

125
Q

Cool, always connect

126
Q

Heat, always connect

A

R-W

R= 24v power/source
Y=Compressor contactor
G= Indoor Fan relay
W= Indoor Heat
C= Low voltage home/Common

127
Q

1st step to diagnose an AC

A

Turn thermostat on

128
Q

Primary side of XFMR is

A

High Voltage

129
Q

Secondary side of XFMR is

A

Low Voltage

130
Q

Low side of XFMR should have a

131
Q

How do you do a safety check

A

Check from
Line 1 to line 2
Line 1 to ground
Line 2 to ground

132
Q

1 cause of electrical failures

A

Loose wires

133
Q

A fuse or breaker trips because

A

Overamping & a short

134
Q

24v to CC coil is not closing, what’s wrong

A

Bad contactor

135
Q

0v to CC coil is not closing, what’s wrong

A

Contactors not bad find where 24v volts is last

136
Q

24v to CC coil is closing, what’s wrong

A

Contactor is doing its job

137
Q

Fan is on vac between R and G

138
Q

Fan is on R & W

139
Q

FR checking VAC across a NC w/o coil energized

140
Q

FR checking VAC across a NO w/o coil energized

A

Source volts

141
Q

FR checking VAC across a NC with coil energized

A

Source volts

142
Q

FR checking VAC across a NO with coil energized

143
Q

Component that controls many heating elements

A

Heat sequencers

144
Q

What turns on when contactor runs

A

Compressor & condenser fan motor

145
Q

Overcurrent protection device

A

Circuit breaking

Hvac Test (1 decks)

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