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WorksheetsStudy Assistant A (MowExA)
Total questions: 140
Worksheet time: 5hrs 40mins
The normal procedure used when checking out electrical circuits, is to connect the:
Voltmeter and ammeter in series
Voltmeter and ammeter in parallel
Voltmeter in parallel and the ammeter in series
Voltmeter in series and the ammeter in parallel
The instrument used to obtain air velocity values is the:
Pedometer
Hydrometer
Anemometer
Odometer
When required to cut capillary tubing, a mechanic should use a:
Side wheel cutter
File
Hacksaw
Tube cutter
Devices using water columns for measuring small pressures above or below atmospheric pressure, as in air ducts or gas lines are called:
Manometers
Barometers
Micrometers
Thermometers
Which of the following gauges would you use, to check a leaky discharge valve in an compressor head?
Compound gauge
Head gauge
High pressure gauge
Non condensible gas
A ton of refrigeration or air conditioning capacity is equal to:
200 British Thermal Units in one hour
1,200 British Thermal Units in one hour
144,000 British Thermal Units in one day
12,000 British Thermal Units in one hour
Enthalpy is:
All of the answers apply to the question
The entropy less the temperature
Sensible heat less latent heat
The heat content of a substance
If a liquid vapour refrigerant mixture has a quality of 75%, it is:
Saturated
Superheated
Mostly vapour
Mostly liquid
Which of the following is the Rankine Scale for absolute zero?
-273
-460
-100
0
If air has a specific volume of 14 cu. ft./lb., what is its density?
0.625 lbs./cu. ft.
0.0714 lbs./cu. ft.
0.7 lbs./cu. ft.
1.4 lbs./cu. ft.
The heat rejected from an standard air conditioning system equals about:
1.25 times the net refrigeration effect
1.00 times the net refrigeration effect
1.75 times the net refrigeration effect
1.50 times the net refrigeration effect
Sensible heat may be defined as the heat that is required to:
Raise or lower the temperature of 1 pound of a substance 1 degree centigrade
Change the temperature of a substance without changing its state
Raise or lower the temperature of 1 pound of a substance 1 degree Fahrenheit
Change the state of a substance without changing its temperature
Boyle's Law states, that if the temperature remains constant, the pressure varies inversely as the:
Gas state changes
Volume
Absolute temperature
Absolute pressure
What is meant by the expression, "Refrigeration Effect"?
Capacity of the condensing unit
K factor of a coil
Number of heat units absorbed by an evaporator
Amount of BTU in fixture
When one end of an iron bar is heated by a flame, the heat will travel to the other end by:
All the answers apply to the question
Conduction
Convection
Radiation
Latent heat may be defined as the heat that is required to:
Change the state of a substance without changing its temperature
Raise or lower the temperature of 1 pound of a substance 1 degree centigrade
Raise or lower the temperature of 1 pound of substance 1 degree fahrenheit
Change the temperature of a substance without changing its state
In what part of a refrigeration system is superheat greatest?
Discharge line
Suction line
Compressor
Evaporator
How is density expressed?
In cubic feet per pound
By specific volume
By vapour pressure
In pounds per cubic feet
In selecting the size of the condensing units, the capacity is calculated at its:
Highest operating suction pressure
Lowest operating suction pressure
Lowest operating condensing pressure
Highest operating condensing pressure
How many BTU's must be added to 10 lbs. of ice stored at 20 degrees F.,to convert it to water at 35 degrees F.?
153
1530
294
2940
A fluid:
Must be in the liquid state to be a fluid
Can be either a liquid or a gas
Can be either a liquid or a solid
Cannot exist in a vapour state
Horizontal piping runs should:
Pitch toward the compressor
Pitch away from the compressor
Be level
Pitch in the direction of flow
Suction risers are normally sized for oil return on the basis of:
No load
Normal load
Minimum load
Maximum load
Suction lines for multiple evaporators are connected to a common suction line. How should the connections be made to the common or main suction line?
At the side
On the top
At an angle of 45o
On the bottom
Suction lines are usually sized for:
2 pounds pressure drop
2 degree temperature change
1 degree temperature change
1 pound pressure drop
By using nitrogen within the piping during brazing operation:
Exterior scale formation is minimized
Discolouration is prevented
The explosion hazard is confined
Copper oxide formation is prevented
Why is a double suction riser required on some installations?
To save space
To increase capacity
To assist in oil return
To lower installation costs
In sizing pipelines in a reciprocating refrigeration system, the most critical line is the:
Discharge line
Condenser drain line
Suction line
Liquid Line
A suction line loop should:
Go around the compressor
Go down to floor level
Be 8' high
Rise to the top of the evaporator
Short forged flare nuts are preferred over the long forged flare nuts because they:
Overcome the effect of frost
Are easier to install
Save brass
Allow for sharper bends
The acceptable minimum gas velocities which should be maintained in horizontal runs of suction lines is:
750 F.P.M.
1500 F.P.M.
500 F.P.M.
900 F.P.M.
Flash gas in the liquid line:
Reduces system capacity
Is caused by too much refrigerant
Keeps the liquid line cool
Helps push liquid refrigerant up the riser
Consideration of sub-cooling to remove flash gas should be given at:
Liquid lifts above 30 feet
Liquid lifts above 15 feet
Liquid lifts above 45 feet
All times
Why must the flux be removed after soldering and brazing?
To help one see the quality of the job
Make a stronger joint
To prevent corrosion
Polish the joint
If all the nitrogen used for pressure testing an Refrigeration System is not removed, what will the most serious effect be?
High suction pressure
Formation of nitric acid
Formation of copper nitrate
High head pressure
When piping two or more compressors in parallel, care should be taken to:
Make piping slope to one compressor
Insulate lines between compressors
Install oil equalizer line
Make sure suction lines have correct I.D. ratio
Oil in the crankcase of a compressor foams because:
The wrong type of oil is used
The suction pressure has been reduced
The crankcase is too hot
Overcharge of oil
Which of the following is a thermodynamic property of refrigerants?
Flammability
Leakage tendency
Enthalpy
Odour
In a mixture of oil and a miscible refrigerant, which results in the highest percentage of refrigerant in the mixture?
High temperature, high pressure
Low temperature, low pressure
High temperature, low pressure
Low temperature, high pressure
Which of the following is not a desirable characteristic of a good refrigerant?
Non toxic
High specific volume
High critical temperature
Low boiling point
A compressor with forced lubrication has an oil pressure gauge on the unit reading 65 psi.If the crankcase pressure is 35 psi, what is the net oil pressure to the bearings?
35 psi
100 psi
30 psi
25 psi
Which one of the following is not used in determining compressor displacement?
Revolutions per minute
Number of cylinders
Diameter of the cylinder
Length of piston
A compressor with a displacement of 15 cfm actually pumps 12 cfm. What is its volumetric efficiency?
120%
40%
75%
80%
All refrigeration compressor suction and discharge valves are opened and closed by:
Inherent spring tension
Pressure differentials
Bleed-off pressure
External springs
Clearance volume in a compressor:
Has no effect on compressor capacity
Has an effect on compressor capacity
Varies depending upon compressor speed
Is the same on all compressors
What is the compression ratio of a compressor with a head pressure of 145.3 psig, and a suction pressure of 25.3 psig?
12.8 to 1
8.0 to 1
5.7 to 1
4.0 to 1
What rule-of-thumb can be used for water consumption on water-cooled condensers using city water?
1 1/2 gpm per ton of refrigeration
2 gpm per ton of refrigeration
3 gpm per ton of refrigeration
2 1/2 gpm per ton of refrigeration
Reduced condenser air quantity is not caused by:
High ambient temperature
Dirty fan blades
Prevailing winds
Dirt on the coil
Approximately how much air flow is required per ton by an air cooled condenser?
1,000 cfm per ton
250 cfm per ton
1,500 cfm per ton
500 cfm per ton
In an evaporator or condenser coil, which is the primary and which is secondary surface?
Primary is outside, secondary is inside
Primary is the fin, secondary is the tube
Primary is inside, secondary is outside
Primary is the tube, secondary is the fin
Reducing the quantity of air flow across an evaporator would have what effect:
Lower the suction pressure
Increase the superheat
Raise the head pressure
Increase efficiency
An oversized evaporator coil in a refrigeration system will tend to:
Maintain a high relative humidity
Increase the operating time of the compressor
Have no effect on humidity
Maintain a low relative humidity
If a thermostatic expansion valve hunts severely, we might reduce hunting by:
Reducing the superheat setting
Changing to a liquid charge
Setting the valve for higher superheat
Installing a larger valve
How will a capillary tube which is to long affect the condensing unit?
Its capacity will be decreased
Its capacity will be increased
The condensing unit will be overloaded
Capillary tube design will not affect the condensing unit
The low-side float is controlled by the:
Rate of refrigerant condensation
Evaporator temperature
Rate of refrigerant evaporation
Evaporator pressure
The thermostatic expansion valve has three operating pressures:
Evaporator, bulb and condensing pressure
Evaporator, spring and bulb pressure
Evaporator, spring and suction pressure
Evaporator, spring and adjusting pressure
Liquid flood-back from the evaporator is most likely to occur when a thermostatic expansion valve has a:
Cross charge
Liquid charge
Dry Charge
Vapour Charge
When heat is added to a system being dehydrated by evacuation:
The temperature pressure relationship of water is changed
A high vacuum requirement is still required
The oil will boil
A pressure of below 100 microns is still required
When is it permissible to use the hermetic compressor in the system for evacuation of the system?
On any system
On packaged equipment under 3 tons
On field installed systems over 3 tons
Never
What is most ignored by a customer, owning a packaged air conditioning system having an air conditioning deficiency?
Condensate drainage
Lubrication
Broken belt
Filters
A low pressure control is wired in series with a thermostat and motor. What takes place when the thermostatic expansion valve is stuck in the closed position?
Pressure control cuts out and motor remains inoperative
Pressure control allows the unit to remain running
Pressure control operates on a short cycle
Pressure control is not affected
What indicates a suction valve leak on a reciprocating compressor?
A rapid decrease in head pressure when the compressor is idle
A hissing sound
Inability of the compressor to produce a high vacuum
A decrease in vacuum when the compressor is idle
Routine preventive measures for heat cramps and heat exhaustion are drinking water and taking ?
none of the answers apply
sugar cubes
salt tablets
aspirin
In servicing a system, you find that the running capacitor needs replacing. The capacitance may vary no more than + or - what percent of that capacitor being replaced.
20%
10%
5%
15%
In starting up a chilled water system, the first piece of equipment to start should be the:
Compressor oil pump
Compressor if it has a built-in oil pump
Chilled water pump
Condenser water pump
In water cooled condensers, the water flows :
through the tubes
over the shell
through the fins
over the tubes
In the condenser, the refrigerant vapour condensed back to a liquid form because:
heat flows out of the refrigerant
the condenser coil is hotter than the cooling medium
all of the answers apply to this question
the compressor raised the saturation temp above the temperature of the cooling medium
In checking a unit, you found that you were not getting any liquid at the inlet of the expansion valve. The probable cause is:
Blocked dehydrator
Undercharge
Poor bulb contact
Frozen expansion valve
A refrigeration system has an air-cooled condenser that is located outdoors, the remainder of the system being located indoors. If the system cycle is off during cold weather, the compressor may not start on the next "on" cycle because:
The head pressure may be too high
The evaporator pressure may be too low
The refrigerant may all have migrated to the compressor
All of the answers apply to the question
When checking voltage on start-up, it is important to maintain voltage as close to the name plate rating as:
15%
10%
20%
5%
Abnormally, low suction pressure is undesirable because:
The motor of a hermetic compressor might overheat
Compressor horsepower does not decrease as load decreases
The evaporator loses superheat
Evaporator capacity decreases
Some packaged air conditioners using full hermetic type compressors, are fitted with a thermostatic expansion valve with an internal bleed port. What is the purpose of the bleed port?
Decrease running cycle
Increase evaporator pressure during off-cycle
Keep evaporator from frosting
Maintain full flow through distributor
A belt driven compressor with a 10" diameter flywheel is being operated on a 3 HP condensing unit at 700 RPM, driven by a 1,750 RPM motor with a 4" pulley. The manufacturer uses the same compressor body on a 5 HP condensing unit operating at 1,050 RPM. What size motor pulley would be required with the 5 HP condensing unit?
9" diameter
18" diameter
6" diameter
3" diameter
Oil pressure failure controls are installed on certain compressors and when the compressor is started and oil pressure is built up within the time delay setting, the control will:
Open contact to heater circuit
Close contact to heater circuit
Open contact to main control circuit
Open contact to low pressure control
The abnormality of an "undercharged system" can be mistaken for:
Inadequate condenser
Low compressor capacity
Overcharged system
Restricted system
If an air cooled condensing unit equipped with a low pressure control is located in a basement, which is unheated in winter and the Box to which it is connected is in a warm place, what happens in the system that affects the temperature in the box?
Refrigerant condenses in the compressor
High pressure control fail to go out
Fixture is to cold
Condensing unit runs continuous
The effect which a thermostatic expansion valve with a partially discharged power element, would have on an evaporator is:
An evaporator saturated with refrigerant
A loss of flow of saturated vapour in the evaporator
A high suction pressure
Superheat hunting by the valve
A shell and coil condenser needs cleaning. How would you accomplish this?
Reverse flow of water
Clean with chemicals
Take the ends off and scrape pass cavities
Reamer
The coil of a normally closed lock-out relay is wired in____ with the overload protectors, and in ____ with the compressor contactor holding coil.
Parallel, parallel
Series, Parallel
Parallel, series
Series, series
Static electricity in computer and data processing rooms is generally caused by:
High frictional losses
Low coil temperatures
Low humidity
High humidity
What resistance is there in a set of good, normally closed relay contacts?
10 ohms
5 ohms
0 ohms
15 ohms
When testing a capacitor with an ohmmeter, if the meter goes to the low end of the scale and then slowly returns to the high end, what is the probable condition of the capacitor?
Bad
Good
Shorted
Open
A dual element fuse has:
Two normal one-time fuse links
A thermal cut-out only
A thermal cut-out and a normal fuse link
The ability to carry LRA of a motor, but not to protect against short
Checking the secondary of a transformer, you find the output is 24 volts and 20 amperes. The turns ratio of the transformer is 5 to 1 (primary to secondary). Determine the voltage and amperage of the primary.
120 volts, 4 amperes
120 volts, 100 amperes
240 volts, 50 amperes
240 volts, 2 amperes
Soft iron is most suitable for use in a:
Permanent magnet
Magneto
Natural magnet
Temporary magnet
Impedance consists of:
May include all of the answers
Inductance
Capacitance
Resistance
The total capacitance of two 100 microfarad capacitors connected in series is:
200 microfarads
25 microfarads
50 microfarads
100 microfarads
Operation of the potential relay is based on the principle that:
Starting current is greater than running current
Motors develop counter-emf
Locked-rotor current results in voltage drop in the power lines
Capacitors store electrical energy
What is the secondary voltage of a step-down transformer having primary voltage 110, number of turns in the primary winding 2,200; and number of turns in the secondary winding is 180?
90V
260V
9V
36V
If the inductive reactance in an A-C circuit is greater than the capacitive reactance, such as, in an induction motor or solenoid valve, does the amperage lead or lag the voltage?
Amperage lags
Depends on applied voltage
Has no effect
Amperage leads
The most fundamental rule of static electricity is:
The right-hand rule
Ohm's law
Charges will always attract metal
Like charges repel while unlike charges attract
Where and when should a motor be tested, to determine whether or not it is being supplied electric current of sufficient voltage?
At the motor, while it is starting
At the motor, with switch off
At the entrance switch, with the motor running
At the entrance switch, with the motor disconnected
The amperage drawn by a 240V compressor motor, as compared to 120V compressor motor under the same load conditions is:
1/2
Twice
Equal
4 times
What are the basic voltages that can be taken off a 4-wire, 208 volt system?
208/3/60 and 208/120/1/60
208/3/60
208/3/60 and 220/110/1/60
220/208/3/60 and 220/208/1/60
The most common type of motor starter is the:
Autotransformer type
Star-delta starter
Across the line starter
Primary reactance type
Of several types of overload relays, the least affected by temperature changes is the:
Magnetically operated type
Bi-metal element type
Ambient compensated type
Melting alloy type
Name the type of single-phase motor that requires no starting switch or mechanism.
Repulsion induction
Shaded pole
Split phase
Capacitor start
In a "current relay", the coil is wired in series with:
The starting winding
The starting capacitor
Both the run and start windings
The running winding
A cycle in the electrical terms can be defined as:
One alternation
Four alternations
Three alternations
Two alternations
In an A-C circuit, what properties do you multiply together to get the wattage?
Voltage, amperage and power factor
Voltage, amperage and resistance
Voltage and amperage
Voltage and power
The basic elements of a control system are:
Control device, source of energy and controller
Controller, controlled device and control agent
Source of energy, controller and controlled variable
Coil, control device and controller
If you were called upon to recommend a single element control, for a refrigeration system designed for the evaporator to operate on a defrost cycle, which one of the following controls would you select?
Snap action valve
Temperature-regulating valve
High pressure control
Low pressure control
The term "modulating control" signifies:
A control with several positions between open and closed
A control with infinite positions between open and closed
Either an open or closed position
An electrically operated unit
Feedback is necessary for:
Floating control
Two-position control
All of the answers apply to the question
Proportional control
For outdoor air and exhaust dampers to close with power failure or interruption, a necessary component is:
Single phase double throw thermostat
Spring return motor
Two-position motor
Proportional motor
An actuator for proportional control usually contains:
A bellows
A heat anticipator
Any of the answers apply to the question
A potentiometer
The value at which the controller is set, and represents the desired value of the controlled variable is known as:
Set point
Control point
Offset point
Differential point
The function of a lock-out relay is to:
Re-cycle modulating damper to full open position
Provide power to oil pump after compressor has stopped for one minute
Protect against nuisance trip-outs
Provide motor and start-up protection against re-cycling
If not properly installed, a hot-gas muffler might trap:
Suction gas
Superheated vapour
Hot gas
Oil
The width of an A-belt would be:
1/2 inch
3/4 inch
5/8 inch
3/8 inch
The crankcase pressure regulating valve:
Closes on rise of inlet pressure
Closes on rise of outlet pressure
Opens on rise of outlet pressure
Opens on rise of inlet pressure
The most effective method of installing a vibration eliminator is:
At a right angle to the vibration
Opposite to the vibration
In line with the vibration
At least 12 inches from the source of the vibration
As the temperature of the refrigerant passing through a drier is lowered, the affinity for water of molecular sieve or activated alumina is:
Fluctuates
Increased
Decreased
Does not change
In the hot-gas bypass control method for capacity control, the system component which is bypassed is the:
Distributor
Compressor
Evaporator
Condenser
A liquid to suction refrigerant heat exchanger might cause:
The compressor to overheat
To much sub-cooling for proper operation of the expansion valve
Flash vapour in the liquid line
The suction line to sweat
The purpose of a suction line accumulator is to:
Accumulate excess vapour
Trap liquid refrigerant
Trap and accumulate the non-condensables
Trap oil
Suction line filters must be sized correctly in order to avoid:
Excessive pressure drop in suction line
Floodback to the compressor
Compressor overloading
Expansion valve hunt
Human comfort requires a relative humidity of about:
40%
50%
30%
20%
The wet bulb temperature is the same as the dry bulb temperature when you have:
75% R.H.
100% R.H.
25% R.H.
50% R.H.
The cooling effect produced when sweat evaporates from the skin is a result of:
Heat loss by radiation
None of these
Heat loss by convection
Latent heat loss
As a "rule-of-thumb", what C.F.M. of air through the evaporator is required per ton of air conditioning?
400 C.F.M.
200 C.F.M.
600 C.F.M.
800 C.F.M.
The psychometric chart is a graph of the temperature-pressure relationship of:
Refrigerant
Oil
Steam
Water
The relationship between water vapour content and air temperature is termed:
Humidity ratio
Relative humidity
Humidity index
Relative density
Primarily, reheat is needed to:
Raise the temperature of chilled air
Raise the temperature of dehumidified air
Raise the temperature of humidified air
Temper cool outdoor air
Stratification can be avoided with:
Larger return air grilles
Lowest possible positioning of return air grilles
Sufficient air flow
Larger distribution diffusers
The most efficient type of duct system is the:
Square
Round
Rectangular
Oblong
A damper controls air flow by:
Varying positions
Varying air volume
All of the answers apply to the question
Varying resistance to flow
Air is :
a mixture
an atom
a compound
an element
Air washers are used to fulfill two distinct purposes. These are to:
Neutralize static and pre-cool air
Clean and pre-cool air
Increase humidity and raise temperature
Reduce pollen and add humidity
The refrigerant pressure drop in the condenser is due to
temperature drop
friction
capillary tube action
subcooling
What is the main advantage of a centrifugal pump?
It is self-priming
It is the cheapest means of moving large quantities of fluids
Its motor can be readily changed
It is the best means of obtaining a very high pressure
A pump impeller running in the opposite direction will be indicated, when it:
Draw less current
produce more head and draw more current
produce less head and draw less current
produce less head and draw more current
A three-way valve having two inlets and one outlet is classified as a:
Diverting valve
Two-position valve
Pilot operated valve
Mixing valve
Refrigerant cylinders should be pressure tested every:
4 years
6 years
3 years
5 years
In transferring refrigerant from one cylinder to another, it is a good idea to avoid filling the cylinder more than per cent full.
70%
85%
75%
80%
You and a helper are cleaning parts with a caustic soda solution, and some solution splashes in his eye. First thing you should do is:
Apply mineral oil to prevent further damage
Call a doctor before attempting first aid
Wash with boric acid solution to neutralize
Flush with large amounts of water
What may occur if a cylinder full of liquid refrigerant is left in a warm place for a long period of time?
The refrigerant may begin to decompose
Hydrostatic pressure may burst the cylinder
Nothing will happen, as this is a normal occurrence
Loss of pressure may collapse the cylinder
What precaution must always be used when pressure testing a system with nitrogen?
A dryer must always be installed in the connecting piping to prevent moisture from entering
An oil separator must be installed in the connecting piping to avoid contaminating the system
The nitrogen must not be left in the system more than a few hours, or it will begin to react chemically with the oil and the refrigerant
A pressure regulator must be installed between the cylinder and the system being tested
Where should the vapour seal be applied to an insulated wall?
Between two layers of insulation
Makes no difference
Warm side
Cold side
Respiration is the:
Heat evolved from life process of fruits and vegetables
Air leaks at cooler doors
Sweating on cooler walls
Formation of moisture on meat due to evaporative evolution
