The flashcards below were created by user
TimMyers
on FreezingBlue Flashcards.
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sensible heat is described as
heat that can be measured
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specific heat is defined as
the amount of heat required to raise one pound of a substance one degree Fahrenheit
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Latent heat is defined as
heat used to cause a change of state
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a BTU is
the amount of heat required to raise one pound of water 1 degree Fahrenheit
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1 ton of refrigeration is
2000× 144× 24, 288, 000 BTU/24 hours, and 12,000 BTU/hr
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a room thermostat should be mounted
five feet from the floor
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to provide proper oil return to the compressor
the suction line must be pitch towards the compressor
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what is the purpose of the external equalizer on a TXV
to offset for the pressure drop across the evaporator
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what would be the minimum bending radius on one inch soft copper tubing
5 inches
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what is the heating value of natural gas
1000 BTU/cu ft
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the purpose of a fan control is too
start and stop the fan motor
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a limit control
d energizes the gas firing circuit upon high bonnet temperatures
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an unconfined space is
a space who's volume is greater than 50 cu ft /1000 BTU/h of total input of all gas fired appliances
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what is the total free area of a 15"× 24"combustion air opening used with the metal grill with an unknown free area
270 sq in
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a confined space is
a space whose volume is less than 50 cu ft/ 1000 BTU/ h of total input of all gas fired appliances
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what is the purpose of the reversing valve on the air to air heat pump
it changes the flow of the refrigerant making the indoor coil the outdoor coil on the Outdoor Coil the indoor coil
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which of the following is connected to the top port of a reversing valve
the discharge line in the compressor
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1 horsepower is the same as
746 watts
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and open run winding will be indicated by which of the following using an ohm meter
infinite ohms from run to start
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a grounded condition found with an ohm meter on a compressor motor will be indicated by which of the following
A zero reading from any terminal to compressor housing
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the heat anticipator
is wired in series with the operating contact
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a cooling anticipator
is wired in parallel with the operating contacts
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what is the purpose of the solenoid valve
it controls the flow of a fluid
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which of the following is used in a heat pump to change the indoor coil to the outdoors
a reversing valve solenoid
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which of the following is the correct method for fastening sheet metal joints
steel metal screws
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the adding of heat to a refrigerant that has reached its vapor saturation point is referred to as
superheating the refrigerant
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the specific heat of air is
.24 BTU/lbº Fahrenheit
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Enthelapy is
the measure of the heat content of a substance
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which of the following is permitted to be used pressure checking a refrigeration system
nitrogen
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using Ohm's law what would R= if e=120 and I=40
3
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a circuit having a voltage of 120 volts applied and is drawing two amps would have a resistance of
12 ohms
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which of the following is false about transformers
a step down transformer produces more voltage on the secondary winding than the voltage applied to the primary
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a positive temperature coefficient PTC device is used for which of the following purposes
start assist for PSC motor
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a 24 volt transformer with a rating of 60va has maximum current carring output of
2.5a
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a rectifier is used to
change AC voltage to DC voltage
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a thermistor may be used for which of the following
to provide temperature readout to assist in the starting of a PSC motor and to stop a motor on an overload condition
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which of the following is true about an internal motor temperature cut out
opens the circuit on temperature rise and stops the motor
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which of the following is adjustable on a thermostat
the bi metal strip
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which of the following is a cause of hermedic compressor motor overheating and cutting out on the internal overload device
refrigerant under charge
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the point or pressure setting at which a pressure sensing device interrupt the electrical circuit is known as the
cut out
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which of the following is not a type of a fan switch used on a gas furnace
temperature on - time off
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which of the following is required when the thermostat subbase designed for two 24 volt power sources is used with one power source
hey jump wire is required to be connected between RH and RC terminal
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which of the following is false about the use of direct digital controls
it is a manual control system that requires more maintenance
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the number of poles in a single phase motor determines the
rpm
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and open circuited run capacitor has which of the following affects on a motor
running amperage will be high motor may fail to start and motor will get hot if operation at full load
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how does the run capacitor affect the operation of a capacitor start capacitor Run compressor motor
limits the current through the start winding so the wind ing will not get hot
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which of the following is used in a permanent split capacitor motor
run capacitor
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which of the following Motors has the lowest starting torque
permanent split capacitor
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2 ohms--------A--------------9 ohms
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B--------------7 ohms------------C
refer to the diagram above in on meter indicates the reading shown on the diagram when checking motor winding which of the following is true about the reading
B is common-A is run- C is start
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when identifying common, start and run terminals of an unfamiliar compressor motor, the following resistance reading are measured across the terminals
terminal A to Terminal B =7 ohms
terminal A to Terminal C =2 ohm
terminal B to Terminal c= 2 ohms
which of the following is the correct terminal designation B is common, A is start, C is run
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the potential relay used on a CSCR motor removes which of the following from the motor circuit
start capacitor
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the contacts of a potential relay are between terminals
one and two
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which of the following is not used on a median for cooling electric motors
refrigerant liquid
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the "NO" (normally open)contacts. of a fan relay used on a combination heating and air conditioning system connects to the
common motor tap
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lowering the voltage applied to a motor that is running will cause the current draw of the motor to
increase
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which of the following changes may be used to reduce the speed of an open compressor driven by belt type motor
change the drive pulley to a smaller diameter
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which of the following is a precaution used in replacing belt on a belt driven compressor
A marked match set of belts shall be used when replacing one or more
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a single contact contactor is used in some cases too
provide crankcase heat to the compressor
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all by metal overload devices are designed with snap action to avoid excessive
arcing of the contacts
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which of the following is a factor in determining why an electric motor hums and then shuts off
mechanical problem, load problem, electrical problem
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the boiling temperature of the liquid refrigerant determines the
evaporator coil operating temperatures
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the difference between the boiling refrigerant temperature and the evaporator outlet temperature is known as
superheat
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which of the following is the function of a normal condenser
de superheat the refrigerant, condense the refrigerant ,subcool the refrigerant
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which of the following is true about a vapor charge both used on a thermostatic expansion valve
the valve body is required to be kept warmer than the bulb
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which of the following metering devices controls refrigerant flow by pressure drop
capillary tube
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which of the following is true about capillary tube metering devices they control
refrigerant flow by pressure drop
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what is the purpose in using a low ambient control
to keep the head pressure up to an acceptable level
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the oil pressure control needs a differential in pressure to allow power to pass to the compressor therefore it must have some means to allow the compressor to get started which of the following is used to accomplish this
a time delay is built into the control
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the heat anticipator used in a thermostat with electric heat may be sent by
adding all current draw in the 24 volt heating circuit that passes through the heat anticipator
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which of the following functions may not be incorporated in a low voltage electric heat sequencer
energize the transformer control circuit
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an electric furnace is being replaced with gas fired appliance the electric furnace has an amp draw of 50 amp at 208 volts and a 40 degree temperature rise which of the following furnaces would be required
35496 btuh output (50×208×3413=35495)
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at 70,000 BTuh electric resistance heat furnace has a temperature rise of 50 degree Fahrenheit how many cubic feet per minute of air is required across the electric heating elements of the furnace
3332 ( 70000 ÷ by 1.0505 ×50=3332
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when burned with air 1 cubic foot of natural gas will produce about how many BTU's of heat energy
1050
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A gas furnace has an input rating of 100,000 btuh and a temperature rise of 50 degrees Fahrenheit how much air is moving across the exchanger in CFM's
4975
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and expansion valve uses an external equalizer to
compensate for excessive pressure drop across an evaporator coil
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excessive platinum Plenum (bonnet) temperature in Furnace are prevented by which of the following devices
limit switch
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a pilot is not used with which of the following burner ignition devices
spark to burner
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