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Define Refrigeration:
Refrigeration is cooling by the removal of heat
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Heat is a form of __
energy
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As the temperature of any substance increases, the molecules which make it up vibrate:
Faster
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One pound of refrigerant will take up the most space:
As a gas because it has the lowest density
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Name the two most commonly used scales to measure temperature:
Fahrenheit and Centigrade
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A cooling coil has 40 degree refrigerant inside its tubes while 80 degree air passes over it. Because heat flows "downhill", it will move from:
The coil surface into the air
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The three ways heat is transferred are called ___, ___, ___
Conduction, convection, and radiation
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Which one of these is a good insulator and, therefore a poor conductor?
Polystyrene
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T or F:
A sensible heat change always causes a change in temperature?
True
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T or F:
A latent heat change always causes a change in molecular activity?
True
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T or F:
A thermometer can be used to measure latent heat change?
False
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T or F:
There is a change of state in a substance whenever latent heat is added to it or removed from it?
True
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Total Heat=
Sensible Heat + Latent Heat
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Temperature cannot measure total heat because:
It cannot measure latent heat, which is part of total heat
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BTU stands for ___ ___ ___
British Thermal Unit
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A BTU is the amount of heat required to raise 1 pound of ___ ___F.
water 1 degree
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Define Specific Heat:
It is the amount of heat required to raise 1 pound of a substance 1 degree Fahrenheit.
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The total heat (in BTU) which a pound of any substance contains is called its ___
Enthalpy
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In terms of refrigeration language, the water we drink is:
Subcooled
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The amount of heat transfer and rate of heat transfer are different because:
Amount deals with "how much" while rate deals with "how fast"
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1 ton of refrigeration capacity or cooling load is:
12,000 Btuh
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3 1/2 tons= ___Btuh
42,000
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Define Pressure:
Its force per unit of area
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Which of the following expresses pressure?
Pounds per square inch
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Pressure in an operating refrigeration system is most often measured in ___
psig
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Pressure is measure in ___ when evacuating a system before it is charged with Freon.
In., Hg., Vac.
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What will the gauge pressure reading be for:
14.7 psia ___
0 psig
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What will the gauge pressure reading be for:
Standard atmospheric pressure ___
14.7 psig
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What will the gauge pressure reading be for:
54.7 PSIA ___
40 psig
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As pressure rises saturation temperature ___
rises
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A body has a negative charge when it:
Contains an excess or electrons
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The force acting between two bodies dis-similarly charged:
is referred to as an electrostatic field
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In electrical circuits, the time of doing work is expressed in:
Watts
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The device used in circuits to prevent damage from overloads is called a:
Fuse
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If the resistance is held constant, what happens to power if the current is doubled?
Power is multiplied by 4
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Soft iron is most suitable for use in a:
temporary magnet
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Around a magnet, the external lines of force:
leave the magnet from the north pole and enter the south pole
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When a conductor moves across a magnetic field:
A voltage is induced in the conductor
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When voltage is applied to a conductor, free electrons:
Are impelled along the conductor
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Which of the following is considered to be the best conductor?
Silver
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Electrically operated devices in gas burning equipment use the electricity producing principle of:
Dissimilar metals heated
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If a circuit is constructed so as to allow the electrons to follow only one possible path, the circuit is called a(n):
Series circuit
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In a series circuit, the total current is:
the same through all parts of the circuit
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T or F:
Primary load devices are located in the line voltage circuit?
True
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Most common control circuits operate from ___ volts AC
24
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High voltages, such as 120v or 240v household supplies, are always dangerous. Under certain conditions, however, even low ___ can be lethal
voltages
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What items listed below are considered load devices?
Compressor, indoor fan motor, outdoor fan motor
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T or F:
The indoor fan motor is located in the low voltage circuit?
False
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Thermal overload devices respond to the heat generated by ___ flow.
excessive current
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T or F:
The low pressure and high pressure switch are normally in series with the compressor contactor?
True
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OFM is abbreviated for ___
Outdoor fan motor
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IFM is abbreviated for ___
Indoor fan motor
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On a loss of refrigerant the low pressure switch closes or opens to de-energize the compressor circuit?
Opens
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As the warm air from the room passes over the evaporator what happens to the refrigerant temperature?
It rises
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As superheat at the evaporator outlet increases, what does the metering device do in response?
It opens
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T or F:
Heat is transferred from the indoor air to the outdoor air by the refrigerant?
True
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T or F:
Heat flows from cold to warm?
False
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T or F:
Sensible heat can measured with a thermometer?
True
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Most of the heat transfer in a mechanical refrigeration system takes place because the ___ changes state.
refrigerant
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On an air cooled condenser the fan motor fails, which switch will protect the compressor?
High Pressure Switch
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T or F:
The solenoid uses magnetism to open the valve?
True
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T or F:
The solenoid coil is considered an electrical load in the circuit?
True
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In a circuit with two solenoids the correct wiring method would be to wire in a series or parallel circuit?
Parallel
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The ___ valve regulates and controls the supply ___ to the burners.
gas, gas
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T or F:
A metering device at the evaporator maintains sub-cooling of the refrigerant?
False
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T or F:
Head pressure is read at the evaporator?
False
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T or F:
Capillary tubes are used as metering devices
True
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T or F:
Thermostatic expansion valves automatically adjust flow of refrigerant according to the superheat sensed?
True
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