good to know totals.doc

7/29/2019 Good to Know totals.doc

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Good to Know

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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
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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%
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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


A permanent opening must be within 12 in. of the ceiling

and the other within 12 in. of the floor. Each opening


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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


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


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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


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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.


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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


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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


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_____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%


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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%


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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


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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,


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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


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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


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


connected?



connected tothe compressor start terminal. Terminal 5

isconnected to the compressor commonterminal.

2.A refrigerant number in the 400 series

designates a(n)


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%


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.


within a(n)__________ % range of itsrated voltage.

10%


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.



17. COP

Coefficient of Performance - BTUHoutput/BTUH input


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"
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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




by the Cube of the speed increase of thatmotor.







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



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


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.


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



(2.036 = 29.921/14.696)

34. How do you convert inches of Subtract inches of mercury vacuum from 29.921
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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?



change one pound of water at 212F to steam?970 Btu's



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?


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



49. Name the two most widely used desiccantstoday.

Activated alumina and the zeolites.


0.293 watts

(This is the reciprical of 3.412, or thenumber of BTU's in a Watt.)

51.


equal to _____________ watts in Electrical

energy.

746 Watts


19/39

52. SEER


Adusted to reflect operationalvariables, applies to Air Conditioning.

53. Specific Heat of Dry Air 0.24 Btu/lb


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


for a start capacitor?

50 to 380 uf and 110 to 330

V


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



refrigerant?



specialized facility, and may involve distillation

and other chemical and physical treatments.

77.What is meant by a recycledrefrigerant?



filter-drier to remove or reduce moisture, acidity,and contaminant particles. Recycling may be done


78.What is meant by recovery of arefrigerant?



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.



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


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?


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?


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


22/39

96.When replacing a start capacitor, a variance in capacitance of

________can usually be tolerated.+- 10%

Good to Know,

Central AC


connected?



connected tothe compressor start terminal. Terminal 5

is

connected to the compressor commonterminal.

2.A refrigerant number in the 400 series

designates a(n)


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%



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.


within a(n)__________ % range of itsrated voltage.

10%


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.
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23/39

13. ASHRAE Standard 15Refrigeration equipment room safety

standards

14. ASHRAE Standard 34Classification of refrigerants as to toxicityand flammability.



17. COP

Coefficient of Performance - BTUH

output/BTUH input


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










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




Tp is Total Pressure in a duct systemSp is Static Pressure in a duct system
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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


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



(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.


change one pound of water at 212F to steam?970 Btu's



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?


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


25/39

"C" represent?


"K" represent?Thermal conductivity


"R" represent?Thermal resistance .

47.Minimum suction gas temperature, entering thecompressor, should be controlled at a minimum

superheat of

18F



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.


equal to _____________ watts in Electricalenergy.

746 Watts

52. SEER


Adusted to reflect operationalvariables, applies to Air Conditioning.



55. Standard air Density.075lbs/cf (The reciprocal of Specificvolume)


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



the _____ and the _____

Supply duct pressure, return duct

pressure.


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


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



refrigerant?



specialized facility, and may involve distillationand other chemical and physical treatments.

77.What is meant by a recycledrefrigerant?



filter-drier to remove or reduce moisture, acidity,and contaminant particles. Recycling may be done


78.What is meant by recovery of arefrigerant?



79. What is specific gravity? The weight of a material, especially a liquid,

compared to the weight of 1 cubic foot of water,


27/39

which has an assigned value of 1.

80.



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?



87.

What is the maximum

acceptable voltage dropacross the contacts of a

motor contactor?


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


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?


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%



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


29/39

transformer. Any voltage applied to the


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.


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


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"




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



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


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)




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%


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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


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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?



52.

What is the maximumacceptable voltage drop across

the contacts of a motor

contactor?


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%


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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


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.


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%


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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%


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.





22. Fan law: Convert V(velocity) into CFM CFM = Asqft X Vfpm




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



http://quizlet.com/16541235/print/http://quizlet.com/16541235/print/


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.


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?


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


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


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



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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)


volume.



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 %.


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


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"

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