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Heavy Equipment Technician Period 4 > HET 4 A/C > Flashcards

HET 4 A/C Flashcards

190403 A,B,C

1
Q

Most people feel comfortable at what temperature?

A

70-75°F (21-25°C)

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2
Q

What is the ideal cab humidity level?

A

40-45%

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3
Q

AC adds or removes humidity?

A

Removes humidity

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4
Q

Heat energy moves from hot to cold or cold to hot?

A

Hot to cold

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5
Q

Heat moves in three methods, what are they?

A

Conduction, Convection, Radiation

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6
Q

Where are condensers usually located?

A

Front or Roof of cab

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7
Q

Conduction transfers heat in what way?

A

Heat energy from one particle to another particle

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8
Q

How is heat transferred through convection?

A

by movement of warm gases or liquids

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9
Q

Radiation can be described as?

A

Electromagnetic rays or moving particles moves the heat

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10
Q

Sun heat coming through the window of a cab is what type of heat movement?

A

Radiation

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11
Q

Heat is measured in two ways, what are they?

A

Heat Intensity
and
Heat Quantity

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12
Q

A well running A/C unit will drop the temperature by what?

A

30°F drop from ambient temp

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13
Q

At what temperature does water freeze at?

A

0°C or 32°F

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14
Q

What is the boiling temperature of water?

A

100°C or 212°F

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15
Q

When liquid changes into a solid, it is called?

A

Fusion Freezing

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16
Q

Melting is what types of state changes?

A

Solid changes into a liquid

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17
Q

A liquid has turned into a vapour what has occurred?

A

Evaporation or Vaporization

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18
Q

What can be superheated?

A

Vaporized refrigerant

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19
Q

What does superheat protect compressor from?

A

Liquid refrigerant

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20
Q

What condition is the refrigerant in when it is considered subcooling?

A

Refrigerant is completely liquid

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21
Q

At what temp does R134A boil at?

A

R134A boils at -26°C

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22
Q

How is subcooling degrees found?

A

High side pressure gauge reading (convert to temp) then subtract condenser outlet temp from that.

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23
Q

Why was R-134a preferred over R-12?

A

R-12 destroyed the ozone - R-134a is environment friendly

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24
Q

Refrigerants are usually what colour?

A

No colour

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25
Q

What colour are the containers that have R-134a in it?

A

Light blue (Sky Blue)

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26
Q

What colour are the containers for R-12?

A

White

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27
Q

What colour is the container that has R-22 refrigerants in it?

A

Light Green colour

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28
Q

What temperatures can the AC system get to in the summer?

A

350 PSI

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29
Q

Why should refrigerant not be released to atmosphere?

A

To protect the environment and is economical

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30
Q

What are the three types of refrigerant lubricant?

A

Mineral oil MO
Polyol Ester POE
Polyalkylene Glycol PAG

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31
Q

Mineral oil is used with what type of refrigerant?

A

R-12

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32
Q

POE and PAG lubricants are used in what systems?

A

R-134a

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33
Q

If MO and PAG lubricants are mixed together what will most likely happen?

A

lack of lube faults

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34
Q

What can POE lubricants be mixed with?

A

Mineral oil and PAG

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35
Q

What are the components of an AC system?

A 
Condenser
Compressor
Expansion Valve
Evaporator
Receiver/Dryer
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36
Q

Where is an evaporator usually located?

A

In Cab - to pull heat out

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37
Q

A condenser’s basic purpose is?

A

To give heat to atmosphere

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38
Q

What are the four events the refrigerant undergoes?

A

Expansion
Evaporation
Compression
Condensation

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39
Q

What type of material make up an AC coil?

A

Copper or aluminium

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40
Q

Is the Condenser in the high or low pressure side of the AC system?

A

High pressure side

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41
Q

Is the Compressor part of the high or low pressure side of an AC system?

A

Half is high pressure

Half is low pressure

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42
Q

Is the refrigerant liquid or vapour in the condenser?

A

Half liquid

Half Vapour

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43
Q

As pressure goes up what does temperature do?

A

go UP

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44
Q

Low pressure will have what temperatures?

A

Lower temps

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45
Q

On the high pressure side of the compressor the line will have what in it? (cold, hot, vapour, liquid)

A

Hot Vapour

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46
Q

As ambient temperature goes up what will happen to the temperatures in the AC system?

A

Go up (all sides of the system)

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47
Q

If a compressor gets fluid in it, what would it sound like?

A

Cavitation, will cause damage

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48
Q

Tin plate (reed valve) on a compressor valve plate would indicate inlet or outlet side?

A

Inlet side

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49
Q

Does belt tension matter on the compressor?

A

Yes

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50
Q

What type of clutch does the ac compressor use?

A

stationary electromagnetic

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51
Q

The clutch hub is splined to what component on the compressor?

A

The compressor drive shaft (front of compressor)

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52
Q

What types of access valves are used on the AC systems?

A

Schrader or stem type

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53
Q

For the AC system to work normally what position does the stem type service valve need to be in?

A

Backseat (open)

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54
Q

To isolate a compressor what position does the AC stem type service valve need to be in?

A

Frontseat - closed

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55
Q

What size are the threads on a schrader valve on a AC system?

A

1/4 inch SAE is most common

can see 3/16 SAE flare or metric

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56
Q

What is a common fault for loosing refrigerant?

A

Leaking schrader valve

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57
Q

Are the R-134a quick disconnect fittings the same as all other systems?

A

No, low pressure as a small valve
high pressure has a larger valve
no external threads
Schrader type

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58
Q

What are the classes of condensers?

A

Tube and fin
serpentine
parallel flow

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59
Q

What is the most expensive type of condenser?

A

Tube and Fin

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60
Q

What is the most common type of condenser?

A

Parallel Flow

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61
Q

What is the largest most inexpensive condenser?

A

Parallel Flow

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62
Q

What material is in the receiver/dryer?

A

Filters/Screens and Desiccant

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63
Q

Where is the receiver/dryer mounted in the ac system?

A

Between the condenser and expansion valve

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64
Q

What is important for a technician to know about the desiccant in the receiver/dryer?

A

If it is compatible with the refrigerant used

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65
Q

What are the three functions of a receiver/dryer?

A

Storage of refrigerant
Dryer
Filter

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66
Q

What label is on the receiver/dryer that shows its compatible with R-134a?

A

XH-7 or XH-9

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67
Q

What is installed on the receiver/dryer or moisture indicator, incase of a fire?

A

Fusible Plug

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68
Q

At 240°F, what will happen to the AC system?

A

The fusible plug will open and vent refrigerant to atmosphere

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69
Q

An internally equalized thermal expansion valve has how many capillary tubes?

A

one

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70
Q

Some thermal expansion valves may need what wrapped around them?

A

Insulating material

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71
Q

On thermal expansion valves that are externally equalized, do they always have one temp sensing bulb?

A

They can have multiple up to 17

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72
Q

True or False?

An orifice tube has moving parts and changes how much refrigerant is sent through the system?

A

False

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73
Q

How do the colours of an expansion tube help a technician?

A

Colour shows what refrigerant and how much it allows through

74
Q

What is the normal temperature range for superheat?

A

8-12°F

75
Q

What is the normal temperature range for subcooling?

A

12-21°F

76
Q

A compressor with a green wire is what voltage system?

A

24V

77
Q

A compressor with one black wire needs how many volts to work and grounds to?

A

12V - source to actuate

grounds through body to frame

78
Q

At what degree does water freeze?

A

0°C or 32°F

79
Q

If a condenser starts to become plugged what will be the complaint?

A

No AC in stop/go traffic but works fine at highway speeds

80
Q

On a hot day the technician finds high super heat, and low gauge reading, what could be the fault?

A

TXV may be freezing due to moisture in system

81
Q

A piece of equipment runs in a climate that is usually below 7°F, the technician finds the TXV freezes up regularly. What could be the cause of the fault?

A

Plugs are missing from schrader valves

Ambient temp/air is opening the schrader and moving air/moisture into the AC system

82
Q

What are the three types of HVAC controls?

A

Active controls
Passive (automatic) controls
Combination and supplemental control devices

83
Q

What type of control is used by the operator?

A

Active controls

84
Q

Where are active controls mounted?

A

Dash mounted

85
Q

HVAC air velocity is measured in?

A

Cubic Feet Per Minute CFM

86
Q

Ambient Temperature switches, Multi-function pressure switches, radiator fan clutches and radiator shutter systems are all examples of what type of HVAC control?

A

Combination and supplemental controls

87
Q

How can flow be divided to two areas at the same time?

A

in bi-level position

88
Q

If the gas charge is lost, what is the operators complaint? AND what will the technician notice?

A

AC does not work

Compressor will NEVER run

89
Q

Where is the sensing bulb in the evaporator?

A 
Lower 3rd (coldest)
Evap Outlet
90
Q

What causes the temperature drop in a fixed orifice tube?

A

Pressure difference, pressure drop

91
Q

What could moisture in the system do to an AC system?

A

Cause rust and freezing

92
Q

What is inside an air condition hose that keeps the tiny molecules from escaping?

A

Elastomeric layer - internal barrier liner

93
Q

A detached sensing bulb could cause what fault in the system?

A

Slug the compressor

94
Q

If a sensing bulb is sensing ambient temperature when will the operator complain?

A

On hot days

95
Q

Engine coolant water valves are located where?

A

Upstream from heater core

96
Q

Why would a flow restricter be used in a water valve?

A

To slow the coolant so heat has time to transfer into cab

97
Q

What type of lubricant should be used to install fittings onto AC hose?

A

Mineral oil - does not attract moisture

98
Q

Is refrigerant heavier than air?

A

Yes

99
Q

Where should hoses be checked for leak?

A

On the lower side of hose/fitting

at the hole in the fitting

100
Q

What can prevent coolant hot spots?

A

H fitting in series with heater core

101
Q

What could cause a bad crimp of an AC hose fitting?

A

Worn out crimping tool
Crimping tool not square in press
Wrong/damaged fitting

102
Q

CCOT stands for?

A

Clutch cycling switch

103
Q

Where is hidden heat?

A

In the evaporator, when the state of change happens to the refrigerant but not CHANGE in temperature

104
Q

What state does the refrigerant have to be in to pass through the compressor and not cause damaged?

A

Vapour

105
Q

How is the temperature controlled in the evaporator in a fixed orifice tube system?

A

Cycling the compressor clutch on/off

106
Q

Trinary switch has three functions what are they?

A

Protects against low pressure/temp
Protects against high pressure/temp
Controls shutters

107
Q

How many prongs/connections do trinary switches have?

A

4 prongs

108
Q

What is used in a bunk model to control the AC system in the sleeper?

A

Electrically controlled refrigerant solenoid valve

109
Q

Due to truck idling laws what is used to keep the sleeper temperature comfortable?

A

Fuel fired air heater
or
Auxiliary power units

110
Q

What is used to warm the engine and give problem-free engine starting?

A

Fuel fired coolant heater

111
Q

How much oxygen do we need in our air to survive?

A

9%

112
Q

How much can you fill an AC container?

A

80% MAX

113
Q

What is used to test/pressurized an AC system to check for leaks?

A

Nitrogen only

114
Q

Who approves refrigerant recovery containers?

A

CTC

115
Q

What can a refrigerant identifier diagnose?

A

Purity of refrigerants, propane and butane

and air %

116
Q

When refrigerant is released into atmosphere, how fast does its temperature drop?

A

Instantly

117
Q

How long is the condenser fan on when driving less than 8km/h?

A

180 seconds

118
Q

What is considered low voltage in a 12V system?

A

11V or less

119
Q

What is considered high voltage in a 12V system?

A

Above 16V

120
Q

What is the normal AC compressor delay during engine cranking?

A

15 seconds

121
Q

What are the three types of refrigerant flow control?

A

H-block style thermal expansion valve
Thermal expansion Valves
Fixed orifice expansion tubes

122
Q

What are the normal speeds on an HVAC blow motor?

A

1-4 speeds

123
Q

How many shafts are there on an HVAC blow motor?

A

single or double shaft

124
Q

How many evaporators are on a truck with a sleeper?

A

2 evaporators

125
Q

What is needed to split refrigerant flow on a truck with a sleeper?

A

Refrigerant solenoid valve

126
Q

Where is the Trinary switch located on the AC system?

A

Between condenser and expansion device

127
Q

What three ranges does the trinary switch monitor?

A

High pressure
Low Pressure
MID range pressure - fan/shutter control

128
Q

At what temperature should the CCOT disengage the compressor clutch?

A

32°F

129
Q

If the refrigerant pressure is 24 PSI, what temperature is in the evaporator?

A

32°F

130
Q

What are the 3 information sources when diagnosing HVAC faults?

A

Tech’s own experience and knowledge
Operator
HVAC Testing

131
Q

What are the three abnormal conditions in the AC system?

A
  1. Lower than normal low and high side pressures with warm duct air
  2. Higher than normal low side pressure and lower than normal high side pressure and warm duct air
  3. Higher than normal low side and high side pressures and warmer than normal air ducts
132
Q

The gauges show lower than normal on the low and high side. The duct air is still cool. Why?

A

Operating at low ambient temp (below 65°F)

133
Q

If refrigerant has been over charged what fault could happen to the compressor?

A

Damage Reed Valves - Slugging compressor

134
Q

Cold weather operation can cause what problems with the AC compressor?

A

Slugging

135
Q

If the H-block expansion valve is stuck open, what faults will occur?

A

Slugging compressor
No Super Heat
No meter of refrigerant

136
Q

After 30 minutes of running the vacuum pump how much PSI or In Hg should their be on the compound gauge?

A

15 in Hg

137
Q

A compressor is cycling on and off quickly, what could be the fault?

A

Undercharged system

138
Q

AC drive belt should have how much movement in the belt (full spread)?

A

1/2” per foot

1/4” up and 1/4” down

139
Q

What are the 6 possible air flows?

A 
MAX
NORM
BI-LEVEL
VENT
HEATER
DEFROST
140
Q

Describe the HVAC system when MAX COOL is selected?

A 
Re circulation cab air
No coolant to heater core 
Temp to cold
Floor/Panel air 
defrost is closed
max blower motor
141
Q

In max defrost setting is the ac clutch engaged or disengaged?

A

Engaged, AC compressor is running

142
Q

What are the four steps that make up the recovery process?

A

Recover
Reuse
Recycle
Reclaim

143
Q

True or False

A charge of 200 PSI of Nitrogen is safe.

A

True

144
Q

True or False

Small AC components should be flushed?

A

False - should be replaced

145
Q

Evaporators are worth flushing?

A

Yes

146
Q

At what temperature does a refrigerant container need to be for 10 hours to find out how much air is present?

A

65°F (19°C)

147
Q

What should AC components be flushed to remove contaminates during a rebuild?

A

Refrigerant oils or Approve flushing agent (many are illegal)

148
Q

According to CTC, If temperatures stay below 50°C how full can a refrigerant container be filled?

A

80%

149
Q

According to CTC, a container can only be filled to 60% in conditions where the temperature is over 50°C.
True or Fase

A

True

150
Q

Which Protocol that was signed in Canada that protects the environment?

A

Montreal Protocol

151
Q

What are the three types of UV rays that the Ozone layer protects the earth from?

A

UVB, UVA, UVC

152
Q

How many GWP units does R-134a have?

A

1200 units

153
Q

How far is the ozone layer from the earth’s surface?

A

15-40KM above

154
Q

When should a technician pry on a compressor?

A

NEVER

155
Q

What is the max tension an AC belt should be ?

A

110lbs of tension

156
Q

How often should a visual inspection be done on a HVAC system?

A

6 months

157
Q

Why should you remove a AC compressor belt during a 6 months inspection?

A

Checking bearings
Check the seal
Check the pulley condition

158
Q

How can frozen coolant affect a heater core?

A

Can be deformed or split

159
Q

What could cause an engine to over heat when the AC is on?

A

Wrong/Failed Thermostat

160
Q

What heating system tools are used?

A

Pressure Testing
Hydrometer
Thermostat test

161
Q

Why would a technician comb a evaporator?

A

To break up debris and straighten fins before cleaning with low pressure air/water

162
Q

What pressure should nitrogen be when forcing oil compressor oil in?

A

50PSI

163
Q

After a bubble is made what should be done to confirm it is accurate?

A

Measure the crimp in 3 spots with a micrometer

164
Q

How far should the crimp start on the fitting sleeve?

A

1/4” or 7mm from the sleeve opening

165
Q

What conditions will shut off the AC?

A

Low static refrigerant pressure

Open or Short in air conditioning electromagnetic clutch circuit

166
Q

If a technician opens high and low gauges at the same time on a running engine what could happen?

A

Slug compressor

167
Q

How long should a vacuum of 500 microns be held for by the vacuum pump?

A

20 minutes

168
Q

What is the purpose of the scale for the refrigerant container?

A

Accurate measurement of refrigerant

169
Q

What are the two ranges available on a compound gauge?

A

0-150 PSI

0-30 in Hg

170
Q

What can be done with a manifold gauge set?

A

Safe access to system for diagnosis and checks
Remove Air/Moisture
Recover or Add refrigerant

171
Q

What should be the duct temperature of a CCOT system?

A

46°F

172
Q

In a CCOT system, the technician finds the inlet to the accumulator is warm. What is the fault?

A

Undercharged system

173
Q

When retrofitting a R-12 system to a R-134a system, how much should the system be recharged to? (%)

A

80%

174
Q

What can be used to test pressure switches to make sure they are working correctly?

A

Nitrogen

175
Q

Without a manufacture specification around how much oil can be put into a compressor? (max oz)

A

8oz

176
Q

A R-134a system needs how many cubic inches of desicant?

A

15 Cubic inches

177
Q

When pulling a vacuum (evacuating) an AC system, how many microns should be held in vacuum for 5 minutes to prove the system is leak free?

A

500 microns for 5 minutes

178
Q

What is the fastest way to recharge an AC system? Vapour or Liquid

A

Liquid

179
Q

True or False

Oil can be added to a system during evacuation?

A

True

180
Q

HRAI stands for?

A

Heating, Refrigerating and Air Conditioning Institute of Canada

Heavy Equipment Technician Period 4 (13 decks)

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