Upload
tinhlaing
View
214
Download
0
Embed Size (px)
Citation preview
7/29/2019 Good to Know totals.doc
1/39
Good to Know
/_x
1. 1 gal #2 oil = BTU's 140,000 Btu's
2. 1 psi converted to wc 2.31ft w.c. or 27.72" w.c.3. 1 Watt = BTU's 3.414 BTU's
4.A Current of 2 A flows through a lamp thathas a resistance of 25 ohms. Determine the
power consumption
100 watts
5.
A furnace is rate at 120,000 Btu/h. In orderto operate this furnace without additional
combustion air, what would have to be the
minimum cuft of the home.
6,000 cuft MinimumFormula (Total BTU Input of all
Appliances / 1,000) x 50 = Volume
Required )
6.A heat pump operating normally in theheating mode would be expected to have a
supply air temperature in the range of:
85 to 105 degrees
7.A high voltage transformersteps up linevoltage to: _______
approximately 14,000 volts
8.A potential relay has three active terminals.How are they numbered, and how are they
connected?
Terminal 1 is connected to one side of
the start capacitor. Terminal 2 is
connected tothe compressor start terminal. Terminal
5 is
connected to the compressor commonterminal.
9.A refrigerant number in the 400 seriesdesignates a(n)
Zeotropes Blends that change volumetric
composition and saturation temperaturesas they evaporate or condense at a
constant pressure.
10.
A resistor's color bands are (left to right)
brown, red, orange, and silver. What is itsresistance?
12,000 ohms 10%
11.A run capacitor usually has a tolerance
rating of what %?5 %
12.
A transformer has 500 turns on the
primary and 1,500 turns on thesecondary If a voltage of 45 V is
applied to the primary, what is the
voltage developed across the
secondary? (Assume no losses.)
135 volts(Formule is Ep/Es = Np/Ns), cross multiply
and the equation becomes (Ep x Ns = Es xNp) now substitute 45 x 1500 = Es x 500 nextstep, simplify 67500 = Es x 500, next step,
divide both sides by 500 to get the answer,
135 = Es or a simple way. This is a 1 : 3 ratiotransformer. Any voltage applied to the
primary will be 3 times that applied voltage
13. A transformer has a turn ratio of 7:1. 35 volts
http://quizlet.com/16513135/print/http://quizlet.com/16513135/print/http://quizlet.com/16513135/print/http://quizlet.com/16513135/print/http://quizlet.com/16513135/print/7/29/2019 Good to Know totals.doc
2/39
If a voltage of 5 V is developed across
the secondary, what is the voltageapplied to the primary?
14.
A transformer with a turn ratio of 1:3
has a current ratio of
________________
3:1
15.
A typical 3 ton split system residential
heat pump would have auxiliary
electric heating elements of about howmany watts total?
15 to 20 kw
16.A typical glow coil usually operates
on a voltage of less than
12 volts
Don't confuse a glow coil with a hot surface
ignitor
17.
A typical motor is designed to operate
within a(n)__________ % range of its
rated voltage.
10%
18.
After the first contactor in a PWSmotor
is energized, there is a time delay of
________ before the second contactoris energized.
3/4 to 1 1/2 seconds
19. Area of a circle A=xR^2
20. ARIAmerican Refrigeration Institute - Setsstandard for level of purity of refrigerants;
Standards forrefrigerant recovery equipment.
21. ARI Standard 700 Standard for level of purity of refrigerants
22. ARI Standard 740 Standard for refrigerant recovery equipment
23.
As a rule of thumb, how many
air changes per hour should a
room have?
Two to three complete air changes per hour
24.
As related to combustion airrequirements, a combustion
air open with metal louvers
will have a ________ % freearea.
75%
25. ASHRAE
American Society of Refrigeration and Air
Conditioning Engineers - Sets standards for
refrigerant toxicity and flammability; Standards forrefrigeration equipment room safety.
26. ASHRAE Standard 15 Refrigeration equipment room safety standards
27. ASHRAE Standard 34Classification of refrigerants as to toxicity andflammability.
28. BTU content of one cf3 of LP 2,500 BTU's
29. Calculate the power factor of
a load from these instrument
83.33%
http://quizlet.com/16513135/print/http://quizlet.com/16513135/print/http://quizlet.com/16513135/print/http://quizlet.com/16513135/print/7/29/2019 Good to Know totals.doc
3/39
readings: Voltage = 240,
Current = 20, Actual power =4,000
30. Circumference of a circle C = pi X D
31.
Combustion air requirements
for the following:* Appliances in a confined
space.
* Combustion air taken fromoutdoor wall.
A permanent opening must be within 12 in. of the
ceiling and the other within 12 in. of the floor. Eachopening must have a minimum free area of at least 1
sqin. per 4,000 Btu/h of the total input rating of all
appliances within the space, but not less than 100 sqinor less than 3" on any side.
32.
Combustion air
requirements for the
following:* Appliances in a confined
space.
* Combustion air taken
from outdoors throughHorizontal ducts.
A permanent opening must be within 12 in. of the ceiling
and the other within 12 in. of the floor. Each openingmust have a minimum free area of at least 1 sqin. per
2,000 Btu/h of the total input rating of all appliances
within the space, but not less than 100 sqin or less than
3" on any side.
33.
Combustion air
requirements for thefollowing:
* Appliances in a confined
space.* Combustion air taken
from outdoors through
Vertical ducts.
A permanent opening must be within 12 in. of the ceilingand the other within 12 in. of the floor. Each opening
must have a minimum free area of at least 1 sqin. per
4,000 Btu/h of the total input rating of all applianceswithin the space, but not less than 100 sqin or less than
3" on any side.
34.
Combustion air
requirements for thefollowing:
* Appliances in a confinedspace.
* Combustion air to be
taken from one permanentopening communicating
directly with the outside.
One permanent opening, commencing within 12 inches
of the top of the enclosure, shall be provided. Theappliance shall have clearances of at least 1 inch from
the sides and back and 6 inches from the front of theappliance. The opening shall directly communicate with
the outdoors or through a vertical or horizontal duct to
the outdoors, or spaces that freely communicate with theoutdoors and shall have a minimum free area of 1 square
inch per 3,000 Btu/h
35.
Combustion airrequirements for the
following:
* Appliances in a confinedspace.* Combustion air to be
taken from unconfined
space in different stories inthe same building.
Such spaces may be connected by one or more openings
in doors or floors having a total minimum free area of 2square inches per 1,000 Btu/h of total input rating of allappliances.
( Total BTU Input of all Appliances / 1,000 x 2 = Total
Free Area Required )
36. Combustion air
requirements for the
A permanent opening must be within 12 in. of the ceiling
and the other within 12 in. of the floor. Each opening
7/29/2019 Good to Know totals.doc
4/39
following:
* Appliances in a confinedspace.
* Combustion air to be
taken from unconfined
space in the same building.
must have a minimum free area of at least 1 sqin. per1,000 Btu/h of the total input rating of all appliances
within the space, but not less than 100 sqin or less than
3" on any side.
37.
Combustion air
requirements for the
following:* Appliances in a
confined space.
* Combustion inlet airtaken from a ventilated
crawl space.
* Outlet air to
ventilated attic.
A permanent opening must be within 12 in. of the ceilingand the other within 12 in. of the floor. Each opening must
have a minimum free area of at least 1 sqin. per 4,000 Btu/h
of the total input rating of all appliances within the space,but not less than 100 sqin or less than 3" on any side.
38.
Combustion airrequirements for the
following:* Appliances in a
unconfined space.
* Building of unusuallytight construction.
Provide two openings from the outside with an minimumfree area of 1 square inch per 5000 btu input. These ducts
MAY be connected to the return air of the furnace.
39.
Convert 40 psi to an
equivalent pressure
expressed in feet ofwater.
92.4 ft (40 x 2.31)
40. Convert EER to COP COP = EER/3.414
41. COPCoefficient of Performance - BTUH output/BTUH input
Can be used for Heating and Cooling Appliances
42.
Define "unconfined
space" as it relates to
combustion airrequirements.
When the volume of the room or space is equal to or greater
than 50 cubic feet per 1000 btu of the total aggregate of
appliances.
43.Define a Btu and a
calorie.
A Btu is the amount of heat required to raise one pound of
water one degree Fahrenheit. A calorie is the amount of heat
required to raise one gram of water one degree Celsius.
44. Define ampacity
Maximum amount of current that a conductor can carry
without excessive heat loss.
Ampacity is used to size wiring and is found on theequipment name plate.
45. Define ampacityMaximum amount of current that a conductor can carry
without excessive heat loss
46. Define power factorThe ratio of actual power being used, to the power which isapparently being used
7/29/2019 Good to Know totals.doc
5/39
47. Define power factorThe ratio of actual power being used, to the power which is
apparently being used.
48.Describe the phase relationship ofcurrent and voltage in a purely
Capacitive circuit.
Current leads voltage by 90 degs.
(ELI the ICE man)
49.Describe the phase relationship ofcurrent and voltage in a purely
inductive circuit.
The voltage waveform is leading the currentby 90 degs. (ELI the ICE man)
50.Describe the terminal wiringconnections for a current relay.
The "L" terminal is connected to the line
voltage. The "M" terminal is connected tothe motor's run winding. The "S" terminal
is connected to the motor's start winding.
51.Determine the power used by a lampthat has a resistance of 20 ohms and a
12 V source.
7.2 watts
52.
Determine the size of the motor pulley
required to run a compressor at 625RPM, if the flywheel diameter is 16 in.
and the motor speed is 3,450 RPM.
2.9"
53. EER
Energy Efficiency Ratio - Nameplateoutput/Nameplate input
Can be used for Heating and Cooling
Appliances
54. Fan law: Basic fan law formula
BHP2 = BHP1 X ((RPM2 / RPM1)cubed)
Shows that required power of a motor varies
by the Cube of the speed increase of that
motor.
55.Fan law: Convert V(velocity) into
CFMCFM = Asqft X Vfpm
56. Fan law: Convert Vp into FPM FPM = 4005(sqrt of Vp)
57. Fan law: Pully size Formula
DPm X RPMm = DPf X RPMf
DP=Diameter of Pully f=Fan or Driven
m=Motor or DriverQuick formula, Example Want DPf then
multiply DPm by RPMm and divide byRPMf
and so on. Also formula can be written
DPm / DPf = RPMf / RPMm
58. Fan law: The relationship of CFM to RPM change
CFM1/CFM2 = RPM1/RPM2
Doubling RPM doulbles CFM
59. Fan Law: Tp equals? Tp = Sp + Vp
Tp is Total Pressure in a duct
systemSp is Static Pressure in a duct
7/29/2019 Good to Know totals.doc
6/39
system
Vp is Velocity Pressure in aduct system
60. Figure the expected temperature drop across a chiller
Delta T = BTUH/(GPM x 500)
500 = 8.33333 x 60 This
corrects for time wght of water
61. Find Watts when BTU's are known
W = BTU's X .293
.293 is the reciprocal of 3.414,the number of BTU's in a watt.
62.Floor grilles should deliver air at a net velocity of
_______400 to 500 ft/min
63.For a residential split system, the temperature drop ofthe air across an evaporator should be ________ .
Between 18 and 22F.
64.
For a water source heat pump system what is the
normal operating temperature range of the ground
loop water-circulating system?
60F to 95F degs
65.For natural gas applications, an ideal line pressure is
____________ in. w.g.7.0 in. w.g.
66.For natural gas applications, the manifold pressuretypically is set at __________ in. w.g.
3.5 in. w.g.
67.
For sites at altitudes above 2,000 ft, the loss of air
density is about _____% for each _____ ft of
altitude.
4%, 1,000 ft
68. Formula to clock a furnace or boilerBTUH = [(3600 x cuft)/sec] x
cf x 1000
69. High-efficiency furnaces operate with flue gastemperatures between: 100 and 275 degrees
70.How can barometric pressure in inches of
mercury be converted to PSIA?
Divide barometric pressure by
2.036.
(2.036 = 29.921/14.696)
71.How can you calculate the existing
cfm in a warm-air heating system?CFM = BTU's output/(1.08 x Delta T)
72.How can you determine thesynchronous speed of a motor?
SPEED = (120 x Freq)/Number of Poles
73.
How close should take-offs be
installed downstream from an elbow
in the main trunk line?
Not closer than 7 1/2 duct diameters or elbow
widths.
74.
How do head and flow rate
characteristics compare when two
pumps operate in series
In series pumping, each pump delivers the
same flow rate but contributes half the total
head.
75.How do you convert a pressure of
14.696 PSIA to inches of mercury?
2.036 * 14.696 = 29.921 inches of mercury.
(2.036 = 29.921/14.696)
76. How do you convert inches of
mercury
Subtract inches of mercury vacuum from
29.921 and multiply the result by 0.491.
7/29/2019 Good to Know totals.doc
7/39
vacuum to psi a?
77.How do you determine the CFM of
an electrical furnace.CFM = ((E x I) x 3.414))/(1.08 x Delta T)
78.
How do you determine the percent of
voltage unbalance in a 3 phase
circuit?
Step 1: Add together the three voltage
readings:
248 + 236 + 230 = 714VStep 2: Find the "average" voltage. 714/3 =
238V
Step 3: Subtract the "average" voltage fromone of the voltages that will indicate the
greatest voltage difference. 248 - 238 = 10V
Step 4: To find the %: (10/238) x 100 = 4.2%
79.How long is the warm-up period for ahot-surface igniter?
17 seconds
80.
How long should a sling
psychrometer be whirled when taking
a reading?
30 seconds
81.How many air changes per hour does
an average house have?1 1/2 times per hour
82.How many air changes per hournormally are required to prevent the
formation of stagnant regions?
Eight to ten air changes per hour.
83.How many Btu of latent heat are required tochange one pound of water at 212F to steam?
970 Btu's
84.How many Btu of latent heat are required to
change one pound of water to ice.144 Btus
85. How many Btuh equal 1 horsepower? 2,545 Btus (746 x 3.412 = 2545)
86.How many cubic inches of mercury equal one
pound?
2.036 (By dividing 29.92 by
14.696 you come up with the
correct answer)
87. How many grains are there in 1 Lb of water? 7,000 grains.
88.
How many horsepower are required to drive a
compressor that requires 12,725 Btuh to compress
and circulate the gas?
12,725/ 2,545 = 5 hp
89.How should a horizontal run of discharge piping be
pitched?
Away from the compressor at a
slope of at least 1/4 in. per foot
of piping.
90. HSPF
Heating Seasonal PerformanceFactor - Efficiency of Heat
Pumps in the heating cycle only.
BTUH out/BTUH input.Adjusted to reflect operational
Variables
91. If a relay with a VA rating of 20 VA has a control
voltage of 24 V applied to its coil, what current
A = 20/24; A = .833
7/29/2019 Good to Know totals.doc
8/39
does it draw when the armature is pulled all the
way down?
92.
If the average current through the windings of a
three-phase motor is 25 A, and the currentmeasured through one of the individual windings is
28 A, is the maximum allowable current imbalance
being exceeded?
Yes.(The deviation from the average
current
is 3 A. When divided by theaverage current
of 25 A and multiplied by 100,
this amountsto a 12% current imbalance, well
over the 2% limit.)
93.If the total voltage in a simple circuit is 120V and
the total resistance is 40 ohms, solve for power.360 watts (P = E2 / R)
94.If the water flow through a system is doubled,
what happens to the pressure drop?It increases four times
95.
In a balanced three-phase system, the three-phasevoltage can be calculated by multiplying the
voltage across any two legs times
_______________
The square root of 3. (The
product is used to compute theVA rating of a 3 phase
transformer so proper protection
for the transformer can becomputed)
96.In any case, the compressor's discharge line
temperature should not exceed what temperature?225 degrees F
97.In general, what are the recommended local air
velocities for heating? For cooling?
For heating, local air velocities
should be below 40 ft/min. For
cooling, local air velocitiesshould be between 40 and
80 ft/min.
98.In heat load calculations, what does the letter "C"
represent?Thermal conductance
99.In heat load calculations, what does the letter "K"
represent?Thermal conductivity
100.In heat load calculations, what does the letter "R"
represent?Thermal resistance .
101.
In order to achieve complete combustion with
natural gas, each cubic foot of gas must combine
with no less than ______ cubic feet of air with an
additional 5 cubic feet of extra air to ensure thereis enough oxygen for complete combustion.
10 cubic feet
102.
In the process known as flame rectification, what
kind of current is used to prove that there is aflame burning?
Pulsating DC
103.It is usually desirable to maintain commercial
buildings at a positive pressure of approximately .0.01 to 0.03 in. w.g.
104. Low-velocity systems usually operate at less than 2,000 ft/min
7/29/2019 Good to Know totals.doc
9/39
_____ft/min.
105.Mid-efficiency furnaces operate with flue gas
temperatures between:275 and 360 degrees
106.
Minimum suction gas temperature, entering
the compressor, should be controlled at a
minimum superheat of
18F
107.Most motors are designed to operate in an
ambient temperature of not more than40 C or 104 F
108.Name the two most widely used desiccants
today.Activated alumina and the zeolites.
109.Normal CAD cell resistance is _______ with
flame present.less than 1,000 ohms
110.Oil furnaces are vented with ____________venting material.
type L
111.
On a system that has a 12,000 Btu load with
the heat of compression added, what amount
of additional capacity is required in thecondenser?
20%
112. One Btuh of heat equals how many watts?
0.293 watts
(This is the reciprical of 3.412, or thenumber of BTU's in a Watt.)
113.
One horsepower in mechanical energy is
equal to _____________ watts in Electrical
energy.
746 Watts
114.Regarding combustion air requirements,
define "confined space".
When the volume of the room or
space is less than 50 cubic feet per
1000 btu/h of the total input of allappliances.
115.
Replacement refrigerants for R-12 can
increase TEV capacities by as much as
_______. over those of R-12.
20 to 30%
116. SEER
Seasonal Energy Efficiency Ratio -
Adusted to reflect operational
variables, applies to AirConditioning.
117. Specific gravity of LP 1.5sg
118. Specific gravity of natural gas 0.6 sp
119. Specific Heat of Dry Air 0.24 Btu/lb120. Specific heat of natural gas 1000BTU's/cf
121. Standard air Dry air @ 68deg @ 29.92hg"
122. Standard air Density .075lbs/cf (The reciprocal of Specific volume)
123. Standard Air volume 13.33cf/lb Also know as specific volume.
124.Start capacitors Have typical
tolerance Ratings of20 to 25%
7/29/2019 Good to Know totals.doc
10/39
125.
Start capacitors have typical
tolerance ratings of_______________ %
20 to 25%
126.
State the three equations derived
from Ohm's Law for calculatingpower.
127.The "balance point" of a heat
pump is:
The lowest temperature at which the heat pump
can meet the heating requirement for thestructure
128.
The "occupant" load in typical air
conditioning installations is basedon an estimate of _____ Btuh per
person.
400 Btuh
129.
The contacts of a current relay are
normally Open
130.
The contacts of a voltage-type
starting switch (Potentual Relay)
are normally _______________
Closed.
131.The correction factor for pressurereadings amounts to _______ for
Every 1,000 ft of elevation.
0.5 PSI
132.The density of air is the reciprocalof
Specific volume.
133.
The duct static value, for a residential split system,
is the sum of the absolute values of the _____ andthe _____
Supply duct pressure, return
duct pressure.
134.
The life of a motor start capacitor will be
shortened if the voltage across the capacitor
exceeds __________% of the rated voltage
15%
135.The maximum current imbalance of a 3 phase
motor is ________ %
10%
To find current imbalance use
the same steps to find thepercent of voltage unbalance.
Instead use current readings.
136.
The maximum torque that a motor can develop
under increasing load conditions withoutundergoing an abrupt drop in speed and power is
called the _______ torque
Breakdown.
137.The process of a solid turninq directly into a vaporwithout going to a liquid stage is called
Sublimation
138.
The resistance in the individual windings of a three-
phase motor should be within _____ % of each
other.
3% to 5%
7/29/2019 Good to Know totals.doc
11/39
139.The resistance of a cadmium sulfide cell when it
senses the flame:Decreases
140.
The reversing valve has 4 pipe connections. Onepipe connection is on one side of the valve and
three pipe connections are on the opposite side.
What is the center connection on the side with threepipe connections?
Compressor suction connection
141.
The reversing valve has 4 pipe connections. One
pipe connection is on one side of the valve andthree pipe connections are on the opposite side.
What is the single connection on the side opposite
the three connections?
Compressor dischargeconnection
142.
The saturated liquid temperature of arefrigerant is called the ________ . The
saturated vapor temperature IS called the
_____. The difference between these two
temperatures is known as _____
Bubble point, dewpoint, temperature
glide.
143.The service factor of a motor measures
its designed :Overload capacity
144.The temperature difference betweenroom air and refrigerant temperatures is
normally about ______
35 Degs
145.The typical voltage output of a powerpile is _________
750 mvThis is the 'out of circuit' voltage
146.The typical voltage output of a
thermocouple is25 to 35 mv
147. The voltage imbalance between any twolegs of the supply voltage applied to a
three-phase motor must not exceed
___________%
2%
Two % is a good rule of thumb but the
following chart is more appropriate:
To operate a motor when the voltage
betweenphases is unbalanced.
Unbalance............ Decrease load to
1%...................................... 98%2%...................................... 95%
3%...................................... 88%
4%...................................... 82%5% ......................................75%
When the voltages between the threephases ) are not equal, the current
increases dramatically in the motor
7/29/2019 Good to Know totals.doc
12/39
windings, and if
allowed to continue, the motor will bedamaged.
148.The voltage required to open a potential
relay is called thePickup voltage.
149. The voltage that creates a spark on a sparkignition system is approximately:
15,000 volts
150.The weight of water vapor per cubic foot of
dry air is known as _____.Absolute Humidity
151.Under ideal conditions natural gas has anignition temperature of _______ degrees F and
a burning temperature of ________ degrees F.
1,100 degrees, 3,500 degrees
152.What are the acceptable ranges of watervelocity and water volume per ton in chilled
water cooling coils?
A water velocity range of 2 to 6ft/sec and a water volume range of 2
to 6 gpm per ton are acceptable.
153.
What are the three types of winding
connections generally used in three-phasemotors?
Across-the-line (XL), part wind
start (PWS),and wye-delta ("soft start).
154.What are the typical ranges of capacitance and
voltage for a run capacitor?5 to 50 uF and 370 to 440 V
155.What are the typical ranges of capacitance and
voltage for a start capacitor?50 to 380 uf and 110 to 330 V
156.What do the abbreviations MCA and MOCP
stand for?
MCA = Minimum Circuit Amperes
(deals with the wire sizing)MOCP = Maximum Overcurrent
Protection (Deals with the circuit
protection device)157.
What does the voltage rating of a fuse
indicate?
The maximum voltage that the open
fuse will block.
158.What is a common evaporator coil face
velocity in most air conditioning installations?500 ft/min
159. What is AFUE, and what does it apply to.
Annual Fuel Utilization Efficiency -
Applies to combustion heating
equipment. It is expressed in %.
160. What is density? weight per cubic foot.
161. What is entropy?The ratio of the heat content of a gas
to its absolute temperature.
162.What is meant by a reclaimed
refrigerant?
A reclaimed refrigerant is used refrigerant that hasbeen processed and tested for purity to meet ARI
Standard 700. Reclaiming is usually done in a
specialized facility, and may involve distillationand other chemical and physical treatments.
163. What is meant by a recycled
refrigerant?
A recycled refrigerant is one that has been cleaned
by oil separation and at least one pass through a
filter-drier to remove or reduce moisture, acidity,
7/29/2019 Good to Know totals.doc
13/39
and contaminant particles. Recycling may be done
on the job or at an off-site location.
164.What is meant by recovery of a
refrigerant?
Recovery means to remove the entire refrigerantcharge from a system to an external container.
Testing or processing is not necessarily implied.
165. What is specific gravity?The weight of a material, especially a liquid,compared to the weight of 1 cubic foot of water,
which has an assigned value of 1.
166.
What is the approximate cfm for
a furnace input of 70,000 Btuhand a 50F temperature rise
across the furnace?
1,037 CFM
((70,000 X .8)/(1.08 X 50))
167.
What is the approximatevelocity of the flow of cool air
through the rooms of a house
toward the return intake?
50 ft/min or less.
168.
What is the difference between
apparent power and actual
power?
Apparent power is the product of applied voltageand current. It does not take into account the phase
angle between voltage and current that exists.
Actual or useful power is measured with awattmeter.
169.
What is the equation for
determining the fan speed whenthe motor speed and pulley sizes
are known (assuming no belt
slippages)?
RPMm X DIAm = RPMb X DIAbm = motor b = blower
170.What is the equation toconvert Fahrenheit to
Celsius.
C = (F-32) x .56
171.What is the equation used toconvert Celsius readings to
Fahrenheit?
F = (C x 1.8)+32
172.
What is the formula for the
BTUH output of an electricfurnace.
BTUH = (E x I) x 3.414)
173.
What is the heat content of
dry air per degree
Fahrenheit change intemperature?
About 0.24 Btu/lb (Also know as Specific Heat)
Dry air @ 68deg @ 29.92hg"
174.What is the holding voltage
for a potential relay?
The amount of voltage needed to keep the
relay contacts open.
175. What is the maximum
acceptable voltage drop
across the contacts of amotor contactor?
3% of the rated line voltage
Why is this so important? Let's say the voltage dropreading across the points is 8 volts. By dividing the
7/29/2019 Good to Know totals.doc
14/39
voltage by the current through that set of points we get
8/20 = .4 Ohms. Taking this one step further we candetermine the power in watts that is being dissipated
by those points. P(watts) = I x E; P = 20amps x 8volts
= 160 watts. This 160 watts is dissipated as heat. So
what is the point? Glade you asked. Any substantialvoltage drop across a contactors' set of points causes
those points to heat up, even if it is below the 3% level.
This causes a snow ball effect, and the points willdeteriorate faster and faster as the heat dissipated by
the points causes a higher and higher voltage drop.
176.
What is the maximumbrazing alloy flow point
temperature recommended
for the installation of
reversing valves?
1,145F
177.What is the maximum practical distancethat a pump can "lift" (Suction Head) cold
water?
20 ft
178. What is the melting point of 95/5 solder? 450F
179.What is the melting temperature of silver
solder?1,100 to 1,200F
180.What is the purpose of a suction-lineaccumulator on a heat pump?
It protects the compressor against "slop-over" of the liquid refrigerant during a
change in cycle.
181.What is the range of refrigeranttemperatures in direct expansion coils
where dehumidification is required?
What is the range of refrigeranttemperatures in direct expansion coils
where dehumidification is required?
182.What is the recommended value (in ohms)
of a resistor used to discharge a capacitor?15,000 ohm
183.
What is the total resistance of a circuit in
which one 40-Ohm resistor and one 20-
Ohm resistor are connected in parallel?
13.33 Ohms ( 40 x 20 / 40 + 20 )
184.What is the voltage at which a potentialrelay closes?
The dropout voltage.
185.What kind of acids will be present in the
oil of a burned compressor motor?
Hydrochloric acid and hydrofluoric
acid.
(This true for CFC and HCFCrefrigerants and Mineral oil)
186.
What percentage of overall heat dissipated
from the system comes from thecompressor motor?
5 to 10%
187.What should the wiring for a unit be sized
for.125% of its FLA
188. What size resistor can be field installed on two watt 15,000 Ohm
7/29/2019 Good to Know totals.doc
15/39
a start capacitor that uses a potential start
relay.
189.When brazing a reversing valve, what isthe maximum valve body temperature
allowed?
250F
190.When calculating the total current in abalanced three-phase circuit, you must use a
constant factor of :
1.73 (This is the square root of 3)
191.
When replacing a start capacitor, a variance
in capacitance of ________can usually betolerated.
+- 10%
192.
When using a water coil for cooling, what is
the most economical minimum differencebetween the leaving air dry-bulb temperature
and the entering water temperature?
6 to 8F
193.
Which of the following airflow rates is the
most reasonable for a heat pump systemoperating in the heating cycle?
450 cfm per ton
194.
Write the equation used to determine power
in a simple resistive circuit When only
resistance and current are known.
195.
Write the equation used to determine power
in a simple resistive circuit when only
resistance and voltage are known.
Good to Know, Central AC
1.A potential relay has three active terminals.How are they numbered, and how are they
connected?
Terminal 1 is connected to one side of
the start capacitor. Terminal 2 is
connected tothe compressor start terminal. Terminal 5
isconnected to the compressor commonterminal.
2.A refrigerant number in the 400 series
designates a(n)
Zeotropes Blends that change volumetric
composition and saturation temperatures
as they evaporate or condense at aconstant pressure.
3. A resistor's color bands are (left to right) 12,000 ohms 10%
7/29/2019 Good to Know totals.doc
16/39
brown, red, orange, and silver. What is its
resistance?
4.A run capacitor usually has a tolerancerating of what %?
5 %
5.
A transformer has a turn ratio of 7:1. If a
voltage of 5 V is developed across thesecondary, what is the voltage applied to
the primary?
35 volts
6.
A typical motor is designed to operate
within a(n)__________ % range of itsrated voltage.
10%
7. Area of a circle A=xR^2
8. ARI
American Refrigeration Institute - Setsstandard for level of purity of
refrigerants; Standards for refrigerant
recovery equipment.
9. ARI Standard 700Standard for level of purity ofrefrigerants
10. ARI Standard 740Standard for refrigerant recovery
equipment
11.As a rule of thumb, how many air changes
per hour should a room have?
Two to three complete air changes per
hour
12. ASHRAE
American Society ofRefrigeration and Air
Conditioning Engineers - Sets standards forrefrigerant toxicity and flammability;
Standards forrefrigeration equipmentroom
safety.13. ASHRAE Standard 15
Refrigeration equipment room safety
standards
14. ASHRAE Standard 34Classification of refrigerants as to toxicity
and flammability.
15. Circumference of a circle C = pi X D
16. Convert EER to COP COP = EER/3.414
17. COP
Coefficient of Performance - BTUHoutput/BTUH input
Can be used for Heating and Cooling
Appliances
18. Define ampacity Maximum amount of current that a conductorcan carry without excessive heat loss
19. Define ampacity
Maximum amount of current that a conductor
can carry without excessive heat loss.Ampacity is used to size wiring and is found
on the equipment name plate.
20. Determine the size of the motor pulley
required to run a compressor at 625
2.9"
http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/7/29/2019 Good to Know totals.doc
17/39
RPM, if the flywheel diameter is 16
in. and the motor speed is 3,450 RPM.
21. EER
Energy Efficiency Ratio - Nameplateoutput/Nameplate input
Can be used forHeating and Cooling
Appliances
22. Fan law: Basic fan law formula
BHP2 = BHP1 X ((RPM2 / RPM1)cubed)
Shows that required power of a motor varies
by the Cube of the speed increase of thatmotor.
23.Fan law: Convert V(velocity) into
CFMCFM = Asqft X Vfpm
24. Fan law: Convert Vp into FPM FPM = 4005(sqrt of Vp)
25. Fan law: Pully size Formula
DPm X RPMm = DPf X RPMf
DP=Diameter of Pully f=Fan or Driven
m=Motor or DriverQuick formula, Example Want DPf then multiply
DPm by RPMm and divide byRPMf and so on.
Also formula can be written DPm / DPf =RPMf / RPMm
26.Fan law: The relationship of CFM
to RPM change
CFM1/CFM2 = RPM1/RPM2
Doubling RPM doulbles CFM
27. Fan Law: Tp equals?
Tp = Sp + Vp
Tp is Total Pressure in a duct system
Sp is Static Pressure in a duct systemVp is Velocity Pressure in a duct system
28.Floor grilles should deliver air at a
net velocity of _______400 to 500 ft/min
29.
For a residential split system, the
temperature drop of the air across
an evaporator should be
________ .
Between 18 and 22F.
30.
How can barometric pressure in
inches of
mercury be converted to PSIA?
Divide barometric pressure by 2.036.
(2.036 = 29.921/14.696)
31. How can you determine thesynchronous speed of a motor? SPEED = (120 x Freq)/Number of Poles
32.
How close should take-offs be
installed downstream from anelbow in the main trunk line?
Not closer than 7 1/2 duct diameters or elbowwidths.
33.How do you convert a pressure of
14.696 PSIA to inches of mercury?
2.036 * 14.696 = 29.921 inches of mercury.
(2.036 = 29.921/14.696)
34. How do you convert inches of Subtract inches of mercury vacuum from 29.921
http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/7/29/2019 Good to Know totals.doc
18/39
mercury
vacuum to psi a?and multiply the result by 0.491.
35.How long should a slingpsychrometer be whirled when
taking a reading?
30 seconds
36. How many air changes per hourdoes an average house have?
1 1/2 times per hour
37.
How many air changes per hour normally are
required to prevent the formation of stagnant
regions?
Eight to ten air changes per hour.
38.How many Btu of latent heat are required to
change one pound of water at 212F to steam?970 Btu's
39. How many Btuh equal 1 horsepower? 2,545 Btus (746 x 3.412 = 2545)
40. How many grains are there in 1 Lb of water? 7,000 grains.
41.
If a relay with a VA rating of 20 VA has a
control voltage of 24 V applied to its coil, what
current does it draw when the armature ispulled all the way down?
A = 20/24; A = .833
42.
In any case, the compressor's discharge line
temperature should not exceed whattemperature?
225 degrees F
43.In general, what are the recommended local airvelocities for heating? For cooling?
For heating, local air velocities
should be below 40 ft/min. For
cooling, local air velocities shouldbe between 40 and
80 ft/min.
44. In heat load calculations, what does the letter"C" represent? Thermal conductance
45.In heat load calculations, what does the letter
"K" represent?Thermal conductivity
46.In heat load calculations, what does the letter"R" represent?
Thermal resistance .
47.
Minimum suction gas temperature, entering the
compressor, should be controlled at a minimumsuperheat of
18F
48.Most motors are designed to operate in an
ambient temperature of not more than40 C or 104 F
49. Name the two most widely used desiccantstoday.
Activated alumina and the zeolites.
50. One Btuh of heat equals how many watts?
0.293 watts
(This is the reciprical of 3.412, or thenumber of BTU's in a Watt.)
51.
One horsepower in mechanical energy is
equal to _____________ watts in Electrical
energy.
746 Watts
7/29/2019 Good to Know totals.doc
19/39
52. SEER
Seasonal Energy Efficiency Ratio -
Adusted to reflect operationalvariables, applies to Air Conditioning.
53. Specific Heat of Dry Air 0.24 Btu/lb
54. Standard air Dry air @ 68deg @ 29.92hg"
55. Standard air Density .075lbs/cf (The reciprocal of Specificvolume)
56. Standard Air volume13.33cf/lb Also know as specific
volume.
57.Start capacitors Have typical toleranceRatings of
20 to 25%
58.Start capacitors have typical tolerance
ratings of _______________ %20 to 25%
59.The "occupant" load in typical airconditioning installations is based on an
estimate of _____ Btuh per person.
400 Btuh
60.The contacts of a voltage-type startingswitch (Potentual Relay) are normally
_______________
Closed.
61.The correction factor for pressure readingsamounts to _______ for Every 1,000 ft of
elevation.
0.5 PSI
62. The density of air is the reciprocal of Specific volume.
63.The duct static value, for a residential splitsystem, is the sum of the absolute values of
the _____ and the _____
Supply duct pressure, return ductpressure.
64.The life of a motor start capacitor will beshortened if the voltage across the capacitorexceeds __________% of the rated voltage
15%
65.
The saturated liquid temperature of a refrigerant is
called the ________ . The saturated vapor temperatureIS called the _____. The difference between these two
temperatures is known as _____
Bubble point, dewpoint,temperature glide.
66. The service factor of a motor measures its designed : Overload capacity
67.The temperature difference between room air andrefrigerant temperatures is normally about ______
35 Degs
68.
The voltage required to open a potential
relay is called the Pickup voltage.
69.The weight of water vapor per cubic foot of dry air is
known as _____.Absolute Humidity
70.What are the typical ranges of capacitance and voltage
for a run capacitor?5 to 50 uF and 370 to 440 V
71.What are the typical ranges of capacitance and voltage
for a start capacitor?
50 to 380 uf and 110 to 330
V
7/29/2019 Good to Know totals.doc
20/39
72. What do the abbreviations MCA and MOCP stand for?
MCA = Minimum Circuit
Amperes (deals with the wiresizing)
MOCP = Maximum
Overcurrent Protection
(Deals with the circuitprotection device)
73. What does the voltage rating of a fuse indicate?The maximum voltage that
the open fuse will block.
74.What is a common evaporator coil face velocity in
most air conditioning installations?500 ft/min
75. What is density? weight per cubic foot.
76.What is meant by a reclaimed
refrigerant?
A reclaimed refrigerant is used refrigerant that hasbeen processed and tested for purity to meet ARI
Standard 700. Reclaiming is usually done in a
specialized facility, and may involve distillation
and other chemical and physical treatments.
77.What is meant by a recycledrefrigerant?
A recycled refrigerant is one that has been cleaned
by oil separation and at least one pass through a
filter-drier to remove or reduce moisture, acidity,and contaminant particles. Recycling may be done
on the job or at an off-site location.
78.What is meant by recovery of arefrigerant?
Recovery means to remove the entire refrigerantcharge from a system to an external container.
Testing or processing is not necessarily implied.
79. What is specific gravity?
The weight of a material, especially a liquid,
compared to the weight of 1 cubic foot of water,which has an assigned value of 1.
80.
What is the approximate cfm for
a furnace input of 70,000 Btuhand a 50F temperature rise
across the furnace?
1,037 CFM
((70,000 X .8)/(1.08 X 50))
81.
What is the approximate velocity
of the flow of cool air throughthe rooms of a house toward the
return intake?
50 ft/min or less.
82.
What is the equation for
determining the fan speed whenthe motor speed and pulley sizes
are known (assuming no beltslippages)?
RPMm X DIAm = RPMb X DIAbm = motor b = blower
83.What is the equation to convert
Fahrenheit to Celsius.C = (F-32) x .56
84. What is the equation used toconvert Celsius readings to
F = (C x 1.8)+32
7/29/2019 Good to Know totals.doc
21/39
Fahrenheit?
85.
What is the heat content
of dry air per degreeFahrenheit change in
temperature?
About 0.24 Btu/lb (Also know as Specific Heat)Dry air @ 68deg @ 29.92hg"
86.What is the holdingvoltage for a potential
relay?
The amount of voltage needed to keep therelay contacts open.
87.
What is the maximum
acceptable voltage drop
across the contacts of amotor contactor?
3% of the rated line voltage
Why is this so important? Let's say the voltage drop
reading across the points is 8 volts. By dividing the voltage
by the current through that set of points we get 8/20 = .4Ohms. Taking this one step further we can determine the
power in watts that is being dissipated by those points.
P(watts) = I x E; P = 20amps x 8volts = 160 watts. This
160 watts is dissipated as heat. So what is the point? Gladeyou asked. Any substantial voltage drop across a
contactors' set of points causes those points to heat up,even if it is below the 3% level. This causes a snow ball
effect, and the points will deteriorate faster and faster as the
heat dissipated by the points causes a higher and higher
voltage drop.
88.What is the melting point
of 95/5 solder?450F
89.What is the meltingtemperature of silver
solder?
1,100 to 1,200F
90.
What is the
recommended value (inohms) of a resistor used
to discharge a capacitor?
15,000 ohm
91.What is the voltage atwhich a potential relay
closes?
The dropout voltage.
92.
What kind of acids will
be present in the oil of aburned compressor
motor?
Hydrochloric acid and hydrofluoric acid.(This true for CFC and HCFC refrigerants and Mineral oil)
93.What percentage of overall heat dissipated from the system comesfrom the compressor motor?
5 to 10%
94. What should the wiring for a unit be sized for.125% of its
FLA
95.What size resistor can be field installed on a start capacitor that usesa potential start relay.
two watt15,000 Ohm
7/29/2019 Good to Know totals.doc
22/39
96.When replacing a start capacitor, a variance in capacitance of
________can usually be tolerated.+- 10%
Good to Know,
Central AC
1.A potential relay has three active terminals.How are they numbered, and how are they
connected?
Terminal 1 is connected to one side of
the start capacitor. Terminal 2 is
connected tothe compressor start terminal. Terminal 5
is
connected to the compressor commonterminal.
2.A refrigerant number in the 400 series
designates a(n)
Zeotropes Blends that change volumetric
composition and saturation temperatures
as they evaporate or condense at a
constant pressure.
3.
A resistor's color bands are (left to right)
brown, red, orange, and silver. What is itsresistance?
12,000 ohms 10%
4.A run capacitor usually has a tolerance
rating of what %?5 %
5.
A transformer has a turn ratio of 7:1. If avoltage of 5 V is developed across the
secondary, what is the voltage applied to
the primary?
35 volts
6.
A typical motor is designed to operate
within a(n)__________ % range of itsrated voltage.
10%
7. Area of a circle A=xR^2
8. ARI
American Refrigeration Institute - Sets
standard for level of purity of
refrigerants; Standards for refrigerantrecovery equipment.
9. ARI Standard 700Standard for level of purity of
refrigerants
10. ARI Standard 740Standard for refrigerant recovery
equipment11.
As a rule of thumb, how many air changes
per hour should a room have?
Two to three complete air changes per
hour
12. ASHRAE
American Society ofRefrigeration and AirConditioning Engineers - Sets standards for
refrigerant toxicity and flammability;
Standards forrefrigeration equipmentroomsafety.
http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/7/29/2019 Good to Know totals.doc
23/39
13. ASHRAE Standard 15Refrigeration equipment room safety
standards
14. ASHRAE Standard 34Classification of refrigerants as to toxicityand flammability.
15. Circumference of a circle C = pi X D
16. Convert EER to COP COP = EER/3.414
17. COP
Coefficient of Performance - BTUH
output/BTUH input
Can be used for Heating and Cooling
Appliances
18. Define ampacityMaximum amount of current that a conductor
can carry without excessive heat loss
19. Define ampacity
Maximum amount of current that a conductorcan carry without excessive heat loss.
Ampacity is used to size wiring and is found
on the equipment name plate.
20.
Determine the size of the motor pulleyrequired to run a compressor at 625
RPM, if the flywheel diameter is 16
in. and the motor speed is 3,450 RPM.
2.9"
21. EER
Energy Efficiency Ratio - Nameplate
output/Nameplate input
Can be used forHeating and Cooling
Appliances
22. Fan law: Basic fan law formula
BHP2 = BHP1 X ((RPM2 / RPM1)cubed)
Shows that required power of a motor varies
by the Cube of the speed increase of thatmotor.
23.Fan law: Convert V(velocity) into
CFMCFM = Asqft X Vfpm
24. Fan law: Convert Vp into FPM FPM = 4005(sqrt of Vp)
25. Fan law: Pully size Formula
DPm X RPMm = DPf X RPMf
DP=Diameter of Pully f=Fan or Drivenm=Motor or Driver
Quick formula, Example Want DPf then multiply
DPm by RPMm and divide byRPMf and so on.
Also formula can be written DPm / DPf =RPMf / RPMm
26.Fan law: The relationship of CFMto RPM change
CFM1/CFM2 = RPM1/RPM2
Doubling RPM doulbles CFM
27. Fan Law: Tp equals? Tp = Sp + Vp
Tp is Total Pressure in a duct systemSp is Static Pressure in a duct system
http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/http://quizlet.com/16540142/print/7/29/2019 Good to Know totals.doc
24/39
Vp is Velocity Pressure in a duct system
28.Floor grilles should deliver air at a
net velocity of _______400 to 500 ft/min
29.
For a residential split system, the
temperature drop of the air across
an evaporator should be________ .
Between 18 and 22F.
30.
How can barometric pressure in
inches of
mercury be converted to PSIA?
Divide barometric pressure by 2.036.
(2.036 = 29.921/14.696)
31.How can you determine the
synchronous speed of a motor?SPEED = (120 x Freq)/Number of Poles
32.How close should take-offs beinstalled downstream from an
elbow in the main trunk line?
Not closer than 7 1/2 duct diameters or elbowwidths.
33.
How do you convert a pressure of
14.696 PSIA to inches of mercury?
2.036 * 14.696 = 29.921 inches of mercury.
(2.036 = 29.921/14.696)
34.
How do you convert inches of
mercury
vacuum to psi a?
Subtract inches of mercury vacuum from 29.921
and multiply the result by 0.491.
35.
How long should a sling
psychrometer be whirled when
taking a reading?
30 seconds
36.How many air changes per hourdoes an average house have?
1 1/2 times per hour
37.
How many air changes per hour normally are
required to prevent the formation of stagnantregions? Eight to ten air changes per hour.
38.How many Btu of latent heat are required to
change one pound of water at 212F to steam?970 Btu's
39. How many Btuh equal 1 horsepower? 2,545 Btus (746 x 3.412 = 2545)
40. How many grains are there in 1 Lb of water? 7,000 grains.
41.
If a relay with a VA rating of 20 VA has a
control voltage of 24 V applied to its coil, whatcurrent does it draw when the armature is
pulled all the way down?
A = 20/24; A = .833
42.
In any case, the compressor's discharge line
temperature should not exceed whattemperature?
225 degrees F
43.In general, what are the recommended local airvelocities for heating? For cooling?
For heating, local air velocities
should be below 40 ft/min. Forcooling, local air velocities should
be between 40 and
80 ft/min.
44. In heat load calculations, what does the letter Thermal conductance
7/29/2019 Good to Know totals.doc
25/39
"C" represent?
45.In heat load calculations, what does the letter
"K" represent?Thermal conductivity
46.In heat load calculations, what does the letter
"R" represent?Thermal resistance .
47.Minimum suction gas temperature, entering thecompressor, should be controlled at a minimum
superheat of
18F
48.Most motors are designed to operate in an
ambient temperature of not more than40 C or 104 F
49.Name the two most widely used desiccants
today.Activated alumina and the zeolites.
50. One Btuh of heat equals how many watts?0.293 watts(This is the reciprical of 3.412, or the
number of BTU's in a Watt.)
51.
One horsepower in mechanical energy is
equal to _____________ watts in Electricalenergy.
746 Watts
52. SEER
Seasonal Energy Efficiency Ratio -
Adusted to reflect operationalvariables, applies to Air Conditioning.
53. Specific Heat of Dry Air 0.24 Btu/lb
54. Standard air Dry air @ 68deg @ 29.92hg"
55. Standard air Density.075lbs/cf (The reciprocal of Specificvolume)
56. Standard Air volume13.33cf/lb Also know as specific
volume.
57.Start capacitors Have typical toleranceRatings of
20 to 25%
58.Start capacitors have typical tolerance
ratings of _______________ %20 to 25%
59.
The "occupant" load in typical air
conditioning installations is based on an
estimate of _____ Btuh per person.
400 Btuh
60.The contacts of a voltage-type startingswitch (Potentual Relay) are normally
_______________
Closed.
61.The correction factor for pressure readingsamounts to _______ for Every 1,000 ft of
elevation.
0.5 PSI
62. The density of air is the reciprocal of Specific volume.
63.The duct static value, for a residential splitsystem, is the sum of the absolute values of
the _____ and the _____
Supply duct pressure, return duct
pressure.
7/29/2019 Good to Know totals.doc
26/39
64.
The life of a motor start capacitor will be
shortened if the voltage across the capacitorexceeds __________% of the rated voltage
15%
65.
The saturated liquid temperature of a refrigerant is
called the ________ . The saturated vapor temperature
IS called the _____. The difference between these twotemperatures is known as _____
Bubble point, dewpoint,
temperature glide.
66. The service factor of a motor measures its designed : Overload capacity
67.The temperature difference between room air and
refrigerant temperatures is normally about ______35 Degs
68.The voltage required to open a potential
relay is called thePickup voltage.
69.The weight of water vapor per cubic foot of dry air isknown as _____.
Absolute Humidity
70.What are the typical ranges of capacitance and voltage
for a run capacitor?5 to 50 uF and 370 to 440 V
71.What are the typical ranges of capacitance and voltagefor a start capacitor?
50 to 380 uf and 110 to 330V
72. What do the abbreviations MCA and MOCP stand for?
MCA = Minimum Circuit
Amperes (deals with the wiresizing)
MOCP = Maximum
Overcurrent Protection
(Deals with the circuitprotection device)
73. What does the voltage rating of a fuse indicate?The maximum voltage that
the open fuse will block.74.
What is a common evaporator coil face velocity in
most air conditioning installations?500 ft/min
75. What is density? weight per cubic foot.
76.What is meant by a reclaimed
refrigerant?
A reclaimed refrigerant is used refrigerant that hasbeen processed and tested for purity to meet ARI
Standard 700. Reclaiming is usually done in a
specialized facility, and may involve distillationand other chemical and physical treatments.
77.What is meant by a recycledrefrigerant?
A recycled refrigerant is one that has been cleaned
by oil separation and at least one pass through a
filter-drier to remove or reduce moisture, acidity,and contaminant particles. Recycling may be done
on the job or at an off-site location.
78.What is meant by recovery of arefrigerant?
Recovery means to remove the entire refrigerantcharge from a system to an external container.
Testing or processing is not necessarily implied.
79. What is specific gravity? The weight of a material, especially a liquid,
compared to the weight of 1 cubic foot of water,
7/29/2019 Good to Know totals.doc
27/39
which has an assigned value of 1.
80.
What is the approximate cfm for
a furnace input of 70,000 Btuhand a 50F temperature rise
across the furnace?
1,037 CFM
((70,000 X .8)/(1.08 X 50))
81.
What is the approximate velocityof the flow of cool air through
the rooms of a house toward the
return intake?
50 ft/min or less.
82.
What is the equation fordetermining the fan speed when
the motor speed and pulley sizes
are known (assuming no beltslippages)?
RPMm X DIAm = RPMb X DIAb
m = motor b = blower
83.What is the equation to convert
Fahrenheit to Celsius.C = (F-32) x .56
84.What is the equation used toconvert Celsius readings to
Fahrenheit?
F = (C x 1.8)+32
85.
What is the heat contentof dry air per degree
Fahrenheit change in
temperature?
About 0.24 Btu/lb (Also know as Specific Heat)
Dry air @ 68deg @ 29.92hg"
86.
What is the holding
voltage for a potential
relay?
The amount of voltage needed to keep the
relay contacts open.
87.
What is the maximum
acceptable voltage dropacross the contacts of a
motor contactor?
3% of the rated line voltage
Why is this so important? Let's say the voltage drop
reading across the points is 8 volts. By dividing the voltageby the current through that set of points we get 8/20 = .4
Ohms. Taking this one step further we can determine the
power in watts that is being dissipated by those points.P(watts) = I x E; P = 20amps x 8volts = 160 watts. This
160 watts is dissipated as heat. So what is the point? Glade
you asked. Any substantial voltage drop across a
contactors' set of points causes those points to heat up,even if it is below the 3% level. This causes a snow ball
effect, and the points will deteriorate faster and faster as the
heat dissipated by the points causes a higher and highervoltage drop.
88.What is the melting point
of 95/5 solder?450F
89. What is the meltingtemperature of silver
1,100 to 1,200F
7/29/2019 Good to Know totals.doc
28/39
solder?
90.
What is the
recommended value (inohms) of a resistor used
to discharge a capacitor?
15,000 ohm
91.What is the voltage atwhich a potential relay
closes?
The dropout voltage.
92.
What kind of acids will
be present in the oil of aburned compressor
motor?
Hydrochloric acid and hydrofluoric acid.(This true for CFC and HCFC refrigerants and Mineral oil)
93.What percentage of overall heat dissipated from the system comesfrom the compressor motor?
5 to 10%
94. What should the wiring for a unit be sized for. 125% of its FLA
95.
What size resistor can be field installed on a start capacitor that
uses a potential start relay.
two watt 15,000
Ohm
96.When replacing a start capacitor, a variance in capacitance of
________can usually be tolerated.+- 10%
Good to Know, Motors and Electrical
1.A Current of 2 A flows through alamp that has a resistance of 25 ohms.
Determine the power consumption
100 watts
2.A high voltage transformer steps up
line voltage to: _______approximately 14,000 volts
3.
A potential relay has three active
terminals. How are they numbered,
and how are they connected?
Terminal 1 is connected to one side of the start
capacitor. Terminal 2 is connected to
the compressor start terminal. Terminal 5 isconnected to the compressor common terminal.
4.
A resistor's color bands are (left to
right) brown, red, orange, and silver.
What is its resistance?
12,000 ohms 10%
5.A run capacitor usually has a tolerance
rating of what %?5 %
6. A transformer has 500 turns on theprimary and 1,500 turns on the
secondary If a voltage of 45 V is
applied to the primary, what is thevoltage developed across the
secondary? (Assume no losses.)
135 volts(Formule is Ep/Es = Np/Ns), cross multiply
and the equation becomes (Ep x Ns = Es x Np)
now substitute 45 x 1500 = Es x 500 next step,simplify 67500 = Es x 500, next step, divide
both sides by 500 to get the answer, 135 = Es
or a simple way. This is a 1 : 3 ratio
7/29/2019 Good to Know totals.doc
29/39
transformer. Any voltage applied to the
primary will be 3 times that applied voltage
7.
A transformer has a turn ratio of 7:1.If a voltage of 5 V is developed across
the secondary, what is the voltage
applied to the primary?
35 volts
8.
A transformer with a turn ratio of 1:3
has a current ratio of
________________
3:1
9.A typical motor is designed to operatewithin a(n)__________ % range of its
rated voltage.
10%
10.
After the first contactor in a PWS motoris energized, there is a time delay of
________ before the second contactor
is energized.
3/4 to 1 1/2 seconds
11.Calculate the power factor of a load from theseinstrument readings: Voltage = 240, Current =
20, Actual power = 4,000
83.33%
12. Define ampacityMaximum amount of current that aconductor can carry without
excessive heat loss
13. Define ampacity
Maximum amount of current that aconductor can carry without
excessive heat loss.
Ampacity is used to size wiring and
is found on the equipment nameplate.
14. Define power factor
The ratio of actual power being
used, to the power which isapparently being used
15. Define power factor
The ratio of actual power being
used, to the power which is
apparently being used.
16.Describe the phase relationship of current and
voltage in a purely Capacitive circuit.
Current leads voltage by 90 degs.
(ELI the ICE man)
17.
Describe the phase relationship of current and
voltage in a purely inductive circuit.
The voltage waveform is leading
the current by 90 degs. (ELI theICE man)
18. Describe the terminal wiring connections for a
current relay.
The "L" terminal is connected to
the linevoltage. The "M" terminal is
connected to
the motor's run winding. The "S"terminal
7/29/2019 Good to Know totals.doc
30/39
is connected to the motor's start
winding.
19.Determine the power used by a lamp thathas a resistance of 20 ohms and a 12 V
source.
7.2 watts
20.
Determine the size of the motor pulleyrequired to run a compressor at 625 RPM,
if the flywheel diameter is 16 in. and the
motor speed is 3,450 RPM.
2.9"
21. Fan law: Pully size Formula
DPm X RPMm = DPf X RPMf
DP=Diameter of Pully f=Fan or Driven
m=Motor or DriverQuick formula, Example Want DPf then
multiply DPm by RPMm and divide
byRPMf and so on. Also formula can be
written DPm / DPf = RPMf / RPMm
22.Fan law: The relationship of CFM to
RPM change
CFM1/CFM2 = RPM1/RPM2
Doubling RPM doulbles CFM
23.How can you determine the synchronous
speed of a motor?SPEED = (120 x Freq)/Number of Poles
24. How do you determine the percent ofvoltage unbalance in a 3 phase circuit?
Step 1: Add together the three voltagereadings:
248 + 236 + 230 = 714V
Step 2: Find the "average" voltage. 714/3= 238V
Step 3: Subtract the "average" voltagefrom one of the voltages that will indicate
the greatest voltage difference. 248 - 238 =10V
Step 4: To find the %: (10/238) x 100 =
4.2%
25.
If a relay with a VA rating of 20 VA has
a control voltage of 24 V applied to its
coil, what current does it draw when the
armature is pulled all the way down?
A = 20/24; A = .833
26. If the average current through the windings of a
three-phase motor is 25 A, and the current
measured through one of the individual windingsis 28 A, is the maximum allowable current
imbalance being exceeded?
Yes.
(The deviation from the average
currentis 3 A. When divided by the
average current
of 25 A and multiplied by 100,this amounts
to a 12% current imbalance, well
7/29/2019 Good to Know totals.doc
31/39
over the 2% limit.)
27.If the total voltage in a simple circuit is 120V and
the total resistance is 40 ohms, solve for power.360 watts (P = E2 / R)
28.
In a balanced three-phase system, the three-phase
voltage can be calculated by multiplying the
voltage across any two legs times_______________
The square root of 3. (The product
is used to compute the VA rating
of a 3 phase transformer so properprotection for the transformer can
be computed)
29.Most motors are designed to operate in an
ambient temperature of not more than40 C or 104 F
30. One Btuh of heat equals how many watts?
0.293 watts
(This is the reciprical of 3.412, or
the number of BTU's in a Watt.)
31.One horsepower in mechanical energy is equal to
_____________ watts in Electrical energy.746 Watts
32. Start capacitors Have typical tolerance Ratings of 20 to 25%
33.Start capacitors have typical tolerance ratings of_______________ %
20 to 25%
34.
State the three equations derived
from Ohm's Law for calculatingpower.
35.The contacts of a current relayare normally
Open
36.
The contacts of a voltage-type
starting switch (Potentual Relay)are normally _______________
Closed.
37.
The life of a motor start capacitor
will be
shortened if the voltage acrossthe capacitor exceeds
__________% of the rated
voltage
15%
38.
The maximum current imbalance
of a 3 phase motor is ________
%
10%To find current imbalance use the same steps to
find the percent of voltage unbalance. Instead use
current readings.
39.
The resistance in the individual
windings of a three-phase motor
should be within _____ % of
each other.
3% to 5%
40.The service factor of a motor
measures its designed :Overload capacity
41. The voltage imbalance between any 2%
7/29/2019 Good to Know totals.doc
32/39
two legs of the supply voltage appliedto a three-phase motor must not
exceed ___________%
Two % is a good rule of thumb but thefollowing chart is more appropriate:
To operate a motor when the voltage between
phases is unbalanced.
Unbalance............ Decrease load to
1%...................................... 98%2%...................................... 95%
3%...................................... 88%
4%...................................... 82%5% ......................................75%
When the voltages between the three phases )
are not equal, the current increases
dramatically in the motor windings, and ifallowed to continue, the motor will be
damaged.
42.
The voltage required to open a
potential
relay is called the
Pickup voltage.
43.
The voltage that creates a spark on a
spark ignition system is
approximately:
15,000 volts
44.What are the three types of windingconnections generally used in three-
phase motors?
Across-the-line (XL), part wind start (PWS),
and wye-delta ("soft start).
45.What are the typical ranges ofcapacitance and voltage for a run
capacitor?
5 to 50 uF and 370 to 440 V
46.
What are the typical ranges of
capacitance and voltage for a startcapacitor?
50 to 380 uf and 110 to 330 V
47.What do the abbreviations MCA andMOCP stand for?
MCA = Minimum Circuit Amperes (deals
with the wire sizing)MOCP = Maximum Overcurrent Protection
(Deals with the circuit protection device)
48.What does the voltage rating of a fuseindicate?
The maximum voltage that the open fuse willblock.
49.
What is the difference
between apparent power and
actual power?
Apparent power is the product of applied voltage and
current. It does not take into account the phase angle
between voltage and current that exists. Actual oruseful power is measured with a wattmeter.
50. What is the equation for RPMm X DIAm = RPMb X DIAb
7/29/2019 Good to Know totals.doc
33/39
determining the fan speed
when the motor speed andpulley sizes are known
(assuming no belt slippages)?
m = motor b = blower
51.What is the holding voltage
for a potential relay?
The amount of voltage needed to keep the
relay contacts open.
52.
What is the maximumacceptable voltage drop across
the contacts of a motor
contactor?
3% of the rated line voltage
Why is this so important? Let's say the voltage dropreading across the points is 8 volts. By dividing the
voltage by the current through that set of points we
get 8/20 = .4 Ohms. Taking this one step further we
can determine the power in watts that is beingdissipated by those points. P(watts) = I x E; P =
20amps x 8volts = 160 watts. This 160 watts is
dissipated as heat. So what is the point? Glade you
asked. Any substantial voltage drop across acontactors' set of points causes those points to heat up,
even if it is below the 3% level. This causes a snowball effect, and the points will deteriorate faster and
faster as the heat dissipated by the points causes a
higher and higher voltage drop.
53.What is the recommendedvalue (in ohms) of a resistor
used to discharge a capacitor?
15,000 ohm
54.
What is the total resistance ofa circuit in which one 40-
Ohm resistor and one 20-Ohmresistor are connected inparallel?
13.33 Ohms ( 40 x 20 / 40 + 20 )
55.What is the voltage at which a potential relay
closes?The dropout voltage.
56.What percentage of overall heat dissipatedfrom the system comes from the compressor
motor?
5 to 10%
57. What should the wiring for a unit be sized for. 125% of its FLA
58.What size resistor can be field installed on astart capacitor that uses a potential start relay.
two watt 15,000 Ohm
59.
When calculating the total current in a
balanced three-phase circuit, you must use aconstant factor of :
1.73 (This is the square root of 3)
60.
When replacing a start capacitor, a variance in
capacitance of ________can usually be
tolerated.
+- 10%
7/29/2019 Good to Know totals.doc
34/39
61.
Write the equation used to determine power in
a simple resistive circuit When only resistance
and current are known.
62.Write the equation used to determine power ina simple resistive circuit when only resistance
and voltage are known.
Good to Know, Central Heating system
1. 1 gal #2 oil = BTU's 140,000 Btu's2. 1 psi converted to wc 2.31ft w.c. or 27.72" w.c.
3. 1 Watt = BTU's 3.414 BTU's
4.A high voltage transformer steps up
line voltage to: _______approximately 14,000 volts
5.A run capacitor usually has a
tolerance rating of what %?5 %
6.
A transformer has 500 turns on the
primary and 1,500 turns on the
secondary If a voltage of 45 V isapplied to the primary, what is the
voltage developed across thesecondary? (Assume no losses.)
135 volts
(Formule is Ep/Es = Np/Ns), cross multiply
and the equation becomes (Ep x Ns = Es x
Np) now substitute 45 x 1500 = Es x 500 nextstep, simplify 67500 = Es x 500, next step,
divide both sides by 500 to get the answer,135 = Es or a simple way. This is a 1 : 3 ratio
transformer. Any voltage applied to the
primary will be 3 times that applied voltage
7.
A transformer has a turn ratio of 7:1.If a voltage of 5 V is developed across
the secondary, what is the voltage
applied to the primary?
35 volts
8.
A transformer with a turn ratio of 1:3
has a current ratio of________________ 3:1
9.A typical glow coil usually operates
on a voltage of less than
12 voltsDon't confuse a glow coil with a hot surface
ignitor
10.A typical motor is designed to operatewithin a(n)__________ % range of its
rated voltage.
10%
7/29/2019 Good to Know totals.doc
35/39
11. Area of a circle A=xR^2
12.As a rule of thumb, how many air
changes per hour should a room have?Two to three complete air changes per hour
13. ASHRAE
American Society of Refrigeration and Air
Conditioning Engineers - Sets standards for
refrigerant toxicity and flammability;Standards forrefrigeration equipment room
safety.
14. BTU content of one cf3 of LP 2,500 BTU's
15.
Calculate the power factor of a loadfrom these instrument readings: Voltage
= 240, Current = 20, Actual power =
4,000
83.33%
16. Circumference of a circle C = pi X D
17. Define power factorThe ratio of actual power being used, to the
power which is apparently being used.
18.
Determine the size of the motor pulleyrequired to run a compressor at 625
RPM, if the flywheel diameter is 16 in.
and the motor speed is 3,450 RPM.
2.9"
19.
Each opening used to introduce
combustion air into a confined space
must have the total free area of at least:
1 sq in. per 1000 Btu/h input, and not less
than 100 sq in.
20.
Each opening used to introducecombustion air into an unconfined
space must have the total free area of at
least:
1 sq in. per 4000 Btu/h input, and not less
than 100 sq in.
21. Fan law: Basic fan law formula
BHP2 = BHP1 X ((RPM2 / RPM1)cubed)
Shows that required power of a motor varies
by the Cube of the speed increase of thatmotor.
22. Fan law: Convert V(velocity) into CFM CFM = Asqft X Vfpm
23. Fan law: Convert Vp into FPM FPM = 4005(sqrt of Vp)
24. Fan law: Pully size Formula
DPm X RPMm = DPf X RPMf
DP=Diameter of Pully f=Fan or Driven m=Motor
or Driver
Quick formula, Example Want DPf then multiplyDPm by RPMm and divide byRPMf and so on.
Also formula can be written DPm / DPf = RPMf /
RPMm
25.Fan law: The relationship of CFM
to RPM change
CFM1/CFM2 = RPM1/RPM2
Doubling RPM doulbles CFM
26. Fan Law: Tp equals? Tp = Sp + Vp
http://quizlet.com/16541235/print/http://quizlet.com/16541235/print/7/29/2019 Good to Know totals.doc
36/39
Tp is Total Pressure in a duct system
Sp is Static Pressure in a duct systemVp is Velocity Pressure in a duct system
27.Find Watts when BTU's are
known
W = BTU's X .293
.293 is the reciprocal of 3.414, the number ofBTU's in a watt.
28.Floor grilles should deliver air at
a net velocity of _______400 to 500 ft/min
29.For natural gas applications, anideal line pressure is
____________ in. w.g.
7.0 in. w.g.
30.For natural gas applications, themanifold pressure typically is set
at __________ in. w.g.
3.5 in. w.g.
31.
Formula to clock a furnace or
boiler BTUH = [(3600 x cuft)/sec] x cf x 1000
32.
High-efficiency furnaces operate
with flue gas temperatures
between:
100 and 275 degrees
33.
How can you calculate the
existing cfm in a warm-air
heating system?
CFM = BTU's output/(1.08 x Delta T)
34.How can you determine thesynchronous speed of a motor?
SPEED = (120 x Freq)/Number of Poles
35.
How close should take-offs be
installed downstream from anelbow in the main trunk line?
Not closer than 7 1/2 duct diameters or elbow
widths.
36.How do you determine the CFM of
an electrical furnace.CFM = ((E x I) x 3.414))/(1.08 x Delta T)
37.How long is the warm-up periodfor a hot-surface igniter?
17 seconds
38.How many air changes per hour
does an average house have?1 1/2 times per hour
39.
How many air changes per hour
normally are required to prevent
the formation of stagnant regions?
Eight to ten air changes per hour.
40.
If a furnace is installed in a
building of tight construction, what
is the requirement for combustion
air.
If vertical combustion ducts are run, eachopening must have a free area of at least 1 sqin.
per 4,000 Btuh. If horizontal combustion ducts
are run, 1 sqin. per 2,000 Btuh of the toatal inputof all appliances is required.
41. If a furnace is installed in a
confined space, what is the
requirement for combustion air
ne permanent opening must be within 12 in. of
the ceiling and ther other within 12 in. of the
floor. Each opening must have a minimum free
7/29/2019 Good to Know totals.doc
37/39
area of at least 1 sqin. per 1,000 Btuh of the total
input rating of all appliances within the space,but not less than 100 sqin.
42.
If a relay with a VA rating of 20
VA has a control voltage of 24 V
applied to its coil, what currentdoes it draw when the armature is
pulled all the way down?
A = 20/24; A = .833
43.In general, what are therecommended local air velocities
for heating? For cooling?
For heating, local air velocities should be below40 ft/min. For cooling, local air velocities should
be between 40 and
80 ft/min.
44.In heat load calculations, whatdoes the letter "C" represent?
Thermal conductance
45.In heat load calculations, what does the letter "K"
represent?Thermal conductivity
46. In heat load calculations, what does the letter "R"represent?
Thermal resistance .
47.
In order to achieve complete combustion with natural gas,
each cubic foot of gas must combine with no less than______ cubic feet of air with an additional 5 cubic feet of
extra air to ensure there is enough oxygen for complete
combustion.
10 cubic feet
48.In the process known as flame rectification, what kind of
current is used to prove that there is a flame burning?Pulsating DC
49.Low-velocity systems usually operate at less than
_____ft/min.2,000 ft/min
50.Mid-efficiency furnaces operate with flue gas temperatures
between:275 and 360 degrees
51.Most motors are designed to operate in an ambienttemperature of not more than
40 C or 104 F
52. Normal CAD cell resistance is _______ with flame present. less than 1,000 ohms
53.Oil furnaces are vented with ____________ venting
material.type L
54. One Btuh of heat equals how many watts?
0.293 watts
(This is the reciprical of
3.412, or the number of
BTU's in a Watt.)
55.
Regarding combustion air requirements, a "confined space"
is defined as a space whose volume is __________per
1,000 Btuh of the combined input rating of all appliancesinstalled in that space.
50 ft3`
56. Specific gravity of LP 1.5sg
57. Specific gravity of natural gas 0.6 sp
58. Specific Heat of Dry Air 0.24 Btu/lb
7/29/2019 Good to Know totals.doc
38/39
59. Specific heat of natural gas 1000BTU's/cf
60. Standard airDry air @ 68deg @
29.92hg"
61. Standard air Density
.075lbs/cf (The
reciprocal of Specific
volume)
62. Standard Air volume13.33cf/lb Also know as specific
volume.
63. The density of air is the reciprocal of Specific volume.
64.The duct static value, for a residential splitsystem, is the sum of the absolute values of
the _____ and the _____
Supply duct pressure, return duct
pressure.
65.The resistance of a cadmium sulfide cellwhen it senses the flame:
Decreases
66.The service factor of a motor measures its
designed :Overload capacity
67.The typical voltage output of a power pile is_________
750 mvThis is the out of circuit voltage
68.The typical voltage output of a
thermocouple is25 to 35 mv
69.The voltage that creates a spark on a sparkignition system is approximately:
15,000 volts
70.The weight of water vapor per cubic foot of
dry air is known as _____.Absolute Humidity
71.
Under ideal conditions natural gas has an
ignition temperature of _______ degrees F
and a burning temperature of ________degrees F.
1,100 degrees, 3,500 degrees
72.What are the typical ranges of capacitance
and voltage for a run capacitor?5 to 50 uF and 370 to 440 V
73.What does the voltage rating of a fuseindicate?
The maximum voltage that the openfuse will block.
74. What is AFUE, and what does it apply to.
Annual Fuel Utilization Efficiency -
Applies to combustion heating
equipment. It is expressed in %.
75. What is density? weight per cubic foot.
76. What is entropy?The ratio of the heat content of a gas to
its absolute temperature.
77. What is specific gravity?
The weight of a material, especially a
liquid, compared to the weight of 1
cubic foot of water, which has an
assigned value of 1.
78. What is the approximate cfm for a furnace input of 70,000
Btuh and a 50F temperature rise across the furnace?
1,037 CFM
7/29/2019 Good to Know totals.doc
39/39
((70,000 X .8)/(1.08 X
50))
79.What is the approximate velocity of the flow of cool airthrough the rooms of a house toward the return intake?
50 ft/min or less.
80.
What is the equation for determining the fan speed when
the motor speed and pulley sizes are known (assuming nobelt slippages)?
RPMm X DIAm =
RPMb X DIAbm = motor b = blower
81. What is the equation to convert Fahrenheit to Celsius. C = (F-32) x .56
82.What is the equation used to convert Celsius readings to
Fahrenheit?F = (C x 1.8)+32
83.What is the formula for the BTUH output of an electric
furnace.BTUH = (E x I) x 3.414)
84.What is the heat content of dry air per degree Fahrenheit
change in temperature?
About 0.24 Btu/lb (Alsoknow as Specific Heat)
Dry air @ 68deg @
29.92hg"