AC/Cooling Flashcards
1
Q
Two main parts of air conditioning units and locations of them
A
- Evaporator. In ductwork above furnace or in a fan coil in the attic
- Condenser. outdoors.
2
Q
What is refrigerant?
A
A liquid/gas that moves heat
3
Q
Refrigerant enters evaporator as a
A
Cold liquid 75%
Gas 25%
4
Q
Refrigerant enters evaporator as a cold liquid. It removes heat from the house air which is blown across
A
The Cooling coil by a fan
5
Q
As house air cools, water in the house
A
Condenses, reducing humidity
6
Q
Compressor does what
A
Squeezes gas (high-pressure) raising temperature above outdoor temperatures
7
Q
What enters condenser coil?
A
Hot gas
8
Q
After hot gas enters condenser coil, what happens
A
The fan blows outdoor air across the coil, removing heat from the gas
9
Q
As it cools, what happens to refrigerant
A
Condenses into a liquid
10
Q
Does liquid or gas move indoors for AC
A
Liquid 75%
Gas 25%
11
Q
liquid moves indoors and goes through a
A
Pressure reducing device
12
Q
Liquid moves indoors and go through pressure reducing device, which does what
A
Cools the liquid below temperature of House air
13
Q
Liquid passing through evaporator coil does what
A
It is evaporated into a gas again, removing more heat and humidity from house
14
Q
Step-by-step process of A/C from compressor
A
Compressor
Hot gas
Fan
Liquid high temperature, high-pressure
Expansion device
Liquid low temperature low pressure
Evaporator coil in Plenum
Gas, low temperature, low pressure
Suction line
Back to compressor
15
Q
Describe a compressor
A
Pump that moves refrigerant when it is a gas, raising its temperature
16
Q
What is the heart of an A/C system and where is it located?
A
Compressor. Outdoors in condenser cabinet.
17
Q
older and newer compressor types
A
Older= piston type
Newer = scroll type
18
Q
Do not operate AC compressors below these temperatures
A
65°F or 16°C
19
Q
Some compressors have these that must be on 12 to 24 hours prior to compressor starting up
A
Crank case heaters
20
Q
What do crank case heaters do?
A
Make sure there is no liquid refrigerant mixed with lubricating oil
21
Q
Compressor life, expectancies for moderate and hot climates
A
Moderate 10 to 15 years
Hot 8 to 10 years
22
Q
These are 30 to 50% of the cost of an entire system
A
Compressors
23
Q
Compressor should be level within how many degrees
A
10
24
Q
What should be next to a compressor unit?
A
Disconnect for servicing
25
Where does an evaporator coil sit?
In ductwork, downstream of heat exchanger, or in an attic in a fan coil unit
26
Evaporator coil does what
Moves heat from house to refrigerant in the coil
27
What does condenser coil do
Removes heat from refrigerant to outside air
28
Describe the AC coils
Copper or aluminum tubing with thin fins to enhance heat transfer
(Fins are delicate and can be damaged by power washers )
29
What might be the cause of coils getting iced up
If airflow is restricted by a dirty air filter, air might not move quickly enough across the coils and cause ice up
30
Where should condenser units not be located?
Under decks or surrounded by shrubs (restricted airflow)
31
Where should condenser units not be
Near exhaust vents
32
What is required if a coil is in an attic?
An extra condensate pan (“attic drip pan”)
33
Condensate is ideally discharged directly outside. If discharging into a plumbing stack, what is required
A trap
34
Why should primary and auxiliary condensate lines not “Y” together?
Both could be affected by blockage
35
Why should drip pans have their own drain line?
Common drain lines between condensate tray and drip pan, may cause a flood if it plugs
36
What might the consequence be of the drain discharging into a plumbing stack?
It may allow sewer gases to back up into the house through the AC system
37
Describe the function of fans
Move air across coils, picking up or giving off heat
38
Should condenser fans be covered in the winter
Yes
39
Indoor fans are often furnace fans modified for increased airflow. Why?
Colder air is harder to push across evaporator coil, so to speed fans are used. (higher speed in the summer.)
40
How many CFM’s for AC air movement
400 to 450 CFM’s
41
What does CFM stand for?
Cubic feet per minute
42
Which are the small and large refrigerant lines for
Large= gas
Small = liquid
43
Which refrigerant lines are insulated and why?
Larger gas, refrigerant line to prevent condensation, and increase efficiency
44
What is the return line called?
Suction line
45
Is the suction line bigger or smaller?
Bigger
46
Does the suction line have gas or liquid?
Gas
47
Liquid line carries warm or cold liquid
Warm
48
Suction line should slope
Down towards condensing unit at quarter inch per foot
49
Where are refrigerant lines most often damaged
Where they pass through the walls of a house
50
What should you look for when looking for a refrigerant leaks?
Oil residue. Refrigerant will boil off.
51
House air passing across a cold evaporator coil does what
Condenses as it cools
52
Condensate should not discharge below what
Into the space below a floor slab
53
What is the possible issue with adding an AC system to an existing furnace
Ductwork designed for heating systems may be undersized
54
Where are humidifiers mounted?
On furnace ductwork, near the AC, between supply and return
55
Why is a damper needed in humidifier ductwork?
For the summer to prevent short-circuiting of the air flow
56
What is needed when switching between heating and cooling systems
Rebalancing of distribution systems by the duct dampers, supply registers, or return grills
57
Why should the ductwork in attics be insulated?
To prevent heat transfer in the attic with a vapour barrier on the outside to prevent condensation
58
What is the ramification of switching back-and-forth repeatedly from heating and cooling?
Can damage compressors
59
Describe how water cooled AC works
Just like air cooled. Coil in house ductwork evaporates a liquid refrigerant into a gas and draws heat out of the house. Gas is compressed to raise temperature.
60
What is the difference in operation between water cooled AC and air cooled AC
Instead of blowing outside air across the gas to cool, it, water is moved across the condenser coil. (doesn’t have to be outside.)
61
Once water has cooled the gas back into a liquid in a water, cooled AC, what happens to the water?
Warm water is disposed and not drinkable
62
Water cooled coil does the same function as what on air cooled
Same function as outdoor coil. Condenses, refrigerant.
63
Why is recirculating pool water not recommended on water cooled AC
Due to corrosion risks from chlorine
64
What are the three AC system types?
1. Central.
2. Independent- ducted
3. Independent.- ductless
65
In houses with no ductwork, this AC system is added for AC only (no heat)
Independent ducted
66
In an independent duct system, where is the indoor coil located?
In the attic
67
What are the two types of independent ductless AC systems
Split system
Single Component system
68
Describe an AC split system (independent ductless)
Condenser cabinet with the compressor, condenser coil, and the fan on the ground or the roof (same as in a central split system)
69
Where are the evaporator coil and house air fan located in independent ductless split systems
Inside the home
70
Water cooled split systems have these for their interior component
Condensate collection and discharge system
71
Water cooled split systems have how many refrigerant lines joining what
Two refrigerant lines, joining outdoor condenser unit to evaporator inside the home
72
What are water cooled split systems also called
Mini splits
73
Why are split systems quieter?
compressor is remote
74
Split systems can be multizone. Up to how many evaporators
Four
75
Single component water cooled AC systems are also called
Through wall
Package systems
76
Describe a single component AC systems
Self contained systems with condenser, compressor, evaporator in the same cabinet
77
Do split systems or single component systems include supplementary heating elements
Single component
78
What could be the problem with single component AC systems in small rooms
Air can bounce off walls or furniture, and create short cycling
79
Do AC and heat pumps have rated cooling capacity
Yes. Both are expressed in tons.
80
How much is a ton of cooling?
12,000 BTUs per hour
81
What is one BTU
Amount of heat required to raise the temperature of a pound of water by 1°F
82
Typical AC systems are what size
Two and 5 ton
83
Cooling systems are sized by
Calculating the heat gain for the house
84
Heat gain depends on
Climate, size and configuration of house, insulation, types of windows
85
Cooling systems are sized to keep the house
15 to 20°F cooler than outdoors
86
AC provides 1 ton of cooling for every
(Moderate climates)
(Hot climates)
Moderate= 700 -1000 ft.²
Hot= 450-600 square feet
87
Is it better to undersize or oversize AC and why?
Under sizing can perform better because oversizing can short cycle and not remove enough humidity
88
AC life expectancy
15 years
89
What is an evaporative cooler?
Simple AC that pushes outdoor air into the home after adding water to the air to coolant
90
Where can evaporative cooler be mounted?
On the exterior wall or the roof
91
Do evaporative coolers have a return duct
No
92
Where are evaporative coolers used?
Warm, dry climates (southwest)
93
The high volume low speed blower in evaporative cooler does what
Draws outside air into the house through a moist cooling pad. As air passes over wet media, water absorbs heat from the air.
94
Describe the mechanics of evaporative cooler
Rotary tank cooler has a metal screen drum that rotates through a tank of water
95
Evaporative coolers don’t work well when
The outside air is humid
96
Why should an evaporative cooler not be interconnected with heating duct work?
Moist air can cause rot
97
How are central AC systems typically installed
In a split system with condenser at building exterior in the evaporator adjacent to the interior furnace equipment
98
Why do some central ACs have electric heaters on compressors?
To keep lubricating oil from absorbing refrigerant
99
A reading of what percentages of RLA is normal
60 to 90%
More = refrigerant overcharged or bad compressor
100
How high above the ground should be condenser be
4 inches
101
Frost on lines or coils could be from
Insufficient airflow (filter debris)
102
Where can condensate be discharged?
Into laundry, tub, if proper air break is maintained
103
What is suggested to reduce cold air loss?
Trap
104
If furnace or evaporator unit is installed in an attic above a finished ceiling, what is necessary
A secondary condensate line
105
Evaporator coil should be located where
On the down flow side of the heat exchanger
106
Describe heat at a molecular level
Molecules bump into each other under pressure, causing heat
107
What is vaporization?
Liquid becomes gas
(greatest expansion).
(greatest cooling)
108
What does CFC stand for?
Chlorofluorocarbons (banned due to fucking the ozone)
109
Three approved gases
Butane, propane, pentane
110
Do fridges or AC create cold
No. They move heat.
111
Most critical device on refrigerators, and why
Throttling device. (capillary tube.) evaporates liquid.
112
What is the cooling cycle of fridges called?
Vapour compression cycle
113
What does COP stand for and what is the equation?
Coefficient of performance
Output Divided by Input
(heat absorbed divided by power in)
114
What happens when condensation happens on evaporator coil and what can solve this?
Results in frost, impeding process. Heating rods solve this.
115
Where do capillary tubes run on high-efficiency fridges
Inside evaporator exit tube
116
Does refrigerant temperature rise in the evaporator?
No. It’s phase changes.
117
Why is it necessary for the evaporator exit tube absorb heat?
To ensure pure vapour is running back to the compressor. Liquid moves up the capillary tube from the condenser.
118
Describe the function of digital inverter compressor’s
Variable speed to avoid shutting on and off
AC converted to DC
Variable frequency to control motor speed
119
What is a ton of cooling?
1 ton= 2000 pounds of ice
The amount of heat to melt a ton of ice in 24 hours
(12,000 BTU)
120
What is the equation to come up with 12,000 BTUs for a ton of cooling?
144 BTUs per pound
X 2000 pounds
= 288,000 BTU
Divided by 24 hours
=12,000 BTU
121
What is the Latent heat of condensation?
Every pound of ice melted (at 32°F or 0°C) that becomes water requires 144 BTUs per pound
122
How many CFM’s per ton on average?
400 CFM per ton
123
What is CFM a measurement of?
Volume
124
How many cubic feet of air per pound
13.33 ft.³.
125
What is specific heat of air?
Heat needed to raise temperature of 1 pound of a substance 1°F
(.244 BTU)
126
One cubic foot of air weighs
0.741 pounds
127
Why is ice solid?
Heat is a form of energy. (molecules in motion.) molecules are in less motion and are somewhat bonded together.
128
Describe sensible heat
If heat is added, or removed, it changes the temperature of the substance
129
What is latent heat?
If heat is added or removed, it changes the state of the substance
130
Describe saturation
When a substance is in the form of both liquid and vapour
If heat is added or removed, it will change state
131
Describe changing state
Takes a lot of heat energy
Energy that is either gained or released
132
What is boiling?
Changing state (liquid to vapour)
133
What is superheat?
Once the liquid has changed completely into vapor, adding more heat will increase the temperature.
134
What is the equation for superheat? (vapour form.)
Measured temperature - saturation temperature = superheat (vapour form)
135
What is sub cooling?
Once the vapour has changed completely into liquid, removing more heat will decrease temperature
136
What is the equation for sub cooling?
Saturation temperature - measured temperature = sub cooling
137
If you compress, a gas, temperature and pressure increase. What happens to its volume?
Volume reduces
138
At what state does the liquid move through at the metering device
Saturation point (25% vapour 75% liquid)
139
Refrigerant moves through evaporator coil, changing state more and removing heat from air. What point is it at?
Latent (50/50)
140
After the evaporator, what heat does the refrigerant pick up
Sensible heat (no longer latent) 100% vapour going back to compressor as gas - superheat
141
What kind of heat does refrigerant let off after compressor
Sensible heat, condensing back into liquid as fan, cooled it off and dumped into outdoor air
142
What point is refrigerant at through condenser coil?
Saturation point until it is liquid
143
How do you figure out AC unit size
Model number divided by 12
144
Should you pull out the disconnect while AC unit is running
No
145
Possible reasons for icing
Low refrigerant, clogged or airflow issue
146
Describe the compressor
Converts low pressure low temperature gas to high pressure high temperature
147
Is condensation on a condenser OK?
Yes
148
Which is the larger tube on a condenser unit?
Suction line. Should be cool and insulated.
149
Describe the evaporator
Receives low pressure, low temperature liquid and absorbs heat until all the liquid has been vaporized
150
What is before the evaporator coil and what does it do?
Expansion valve reduces pressure temperature in changes to vapour
151
Where is the condensate tray
Evaporator coil
152
When in cooling mode, if there is a return on top and bottom floors, which one should you close
Bottom one. Reduces cold air being sucked back into return.
153
If return is it outside of the room, what does a gap under the door ensure
Room won’t become pressurized and can properly cool
154
These switches turn off compressors as a safety device
Pressure sensing switchers
155
Why is a time delay (3-7 mins) on a compressor needed?
Time delay after shut off, allows pressure to neutralize because pressure at the discharge side is way higher and suction side is Low
156
What does an accumulator do?
Stores liquid refrigerant to prevent it from coming into compressor
157
Approximately how many amps per ton
6 to 7
158
What does LRA stand for?
Locked rotor amperage (current drawn, if locked) 5-6 times more
159
Are you required to inspect all AC units
No. (Window units)
160
Types of heat pumps
Water to water
Water to air
Air to air
Bivalent
161
Purpose of emergency heat switch
Bypass outdoor temperature sensor
162
Ice builds up on outdoor section of a heat pump because
outdoor air has high relative humidity
163
Latent heat point temperature of ice into water
0 degrees C or
32 degrees F
164
Latent heat point temperature of water into steam
100 degrees C or
212 degrees F
165
Materials that coils are made of
Aluminum fins with copper tubing
166
What is latent heat of vaporization?
Warm house air boils cold liquid refrigerant into gas at evaporator coil
167
Temperature drop across inside coil after running for 15 minutes
15 to 20°F
168
Define slugging
When liquid refrigerant enters compressor instead of gas
169
Should evaporator coil be installed upstream or downstream of furnace heat exchanger
Downstream. (Not on the return side.)
170
If condensate line is under negative pressure (upstream of blower) what is required
Trap
171
Do you close the humidifier damper in the summer or winter?
Summer
172
Flexible ducts should be 4 inches away from
Hot equipment
173
What is the number for free on
R22
174
System where the compressor is in a different location from the outdoor coil are called
Triple split
