Re-Fresher #2 Flashcards
An emergency shut off valve may be installed between a pressure vessel and the emergency discharge valve only under certain conditions. T or F?
F
Feeder protection for freon hermetic compressor must never exceed 225% of FLA according to the Canadian electrical code. T or F?
F
Oil failure control protects compressor against loss of oil lubrication by sensing two pressures: crankP and pumpP to achieve netPoilP. This works on principle of heat and bi-metal action. T or F?
T
backward inclined fan is all known as a no load or non overloading fan. True or False?
T
A dual element fuse is used to protect a compressor motor from excessive starting current only. True or False?
F
Voltages that can be obtained from a delta closed distribution transformer are 208/1/60, 208/3/60, 240/3/60, 120/1/60. T or F?
F
The reversing valve as used with a heat pump system should be replaced after a system burnout of 0.5or greater has occurred. T or F?
T
Normal compression ratio for a centrifugal compressor is 5:1. T or F?
F
For accurate readings of liquid line moisture indicators its temp should be 70degF. T or F?
F
Refrigerant 12 driers should be at least 3-5 times as large as driers used for refrigerant 22 or 500. True or False?
F
A CRO is used to control condenser pressure during periods of low ambient temperatures (below 70f) on air cooled condensers. T or F?
F
With direct staging compression systems cooling of freon vapour between the discharge of 1st and inlet of second comp is needed.
T or F?
F
Calcium chloride may be stored in the same equipment room as ammonia as long as it is safe to do so. T or F?
F
Copper and brass is always used with ammonia gas because of their non-corrosive action in the presence of moisture. T or F?
F
Calculation for COP is Btu’s output/kw input x 3425. T or F?
F
A direct acting controller means that, an increase in output energy, as it senses an increase in controlled variable. T or F?
T
Temp sensors of the electrical resistance type will always have a positive temperature coefficient. T or F?
F
Protection for branch circuit feeding a refrigeration hermetic compressor should be sized at _____ of RLA
a) 110%
b) 125%
c) 140%
d) 225%
B
A perfect vacuum can be expressed by what pressure?
a) 0psig
b) 0psia
c) 29.4” hg vac
d) 10 microns
B
The capacity of an evaporative condenser/cooling tower is
a) greater when wet bulb temp is low
b) greater when wet bulb temp is hi
c) lower when wet bulb is low
d) greater when humidity is higher
A
A liquid receiver must be capable of storing what percentage of a system charge?
a) 125%
b) 120%
c) 110%
d) 90%
D
Efficiency of a compressor could be stated as
a) how cold suction line is compared to discharge
b) how hot condenser is
c) diff between high and low gauge
d) none of the above
D
What is the safety device located and installed on a gauge glass level indicator in case of breakage?
a) hand valve
b) solenoid valves
c) ball check pins
d) ball check valves
D
A sample evap coil operates at a design TD of 8F. What will the relative humidity in the condition space?
a) 80-90%
b) 70-80%
c) over 90%
d) 90%
C
Normal face velocity or air flow across a unit cooler?
a) 1500-2000fpm
b) 500-600fpm
c) under 500fpm
d) over 500fpm
B
Oversizing evaporator system effects
a) higher humidity
b) lower humidity
c) make unit efficient
d) bring space temp down in less time
B
capacity of a fin and tube evap is controlled by?
a) compressor unloaders
b) coil splitting
c) vary air flow
d) none of the above
B
To achieve stable shell and tube evap control what system characteristic is required?
a) constant air or water flow
b) constant water flow
c) constant air flow
d) proper metering device
B
Temp rise above ambient for a motor?
a) 40c
b) 40f
c) raise of 32f
d) raise of 32C
A
If you have a lower pressure switch that is equipped with a range adjustment screw, what part of the control must be adjusted first?
A
Why would you install two pressure relief valves in parallel on a large capacity system?
a) Valve too close to inside walls of building
b) When two valves needed to service
c) when one valve capacity is not enough
d) all of the above
B
How can water quality be controlled in a cooling tower used for condenser water?
a) adding required impurities
b) ensuring bleed off entering is right
c) ensuring bleed off leaving is right
d) all of the above
C
What is standard air conditon when dealing with ac systems?
a) 72f
b) 70f
c) 68f
d) none
B
Instrument used to check insulation value of an electric motor
a) ohm meter
b) amp metrer
c) megohm meter
d) volt meter
c
What is the purpose of a liquid line solenoid as used with refrigeration system installations?
a) prevents flooding during operation of compressor
b) prevents flash gas in liquid line
c) used on pump down systems
A
Current relay coil is located
a) in series with compressor start winding
b) in series with compressor run winding
c) across start and run winding
d) parallel with run winding
B
If you purge a system with nitrogen and some remains when the process is complete and the system starts up
a) low head pressures
b) system will operate in vacuum
c) high head pressures
d) low back pressure and high head pressure
C
thicker valve plate used on compressor. what happens to eff%?
a) decrease
b) increase
c) stays same
d) nothing
a
If suction pressure was to increase and discharge to remain same, what would happen to compressor capacity?
a) increase
b) decrease
c) stay same
d) nothing
A
On a rotary compressor a check valve is installed on the _______ to prevent equalization in the off cycle
a) liquid line
b) suction line
c) discharge line
C
Ol failure control operates on the principle of?
a) heat and bi metal action
b) temperature
c) pressure
d) time and manual operation
A
A commercial refrigeration system has 10F fluctuation in suction pressure.
a) evap is over sized
b) evap is under sized
c) expansion vale is under sized
d) expansion valve oversized
D
Why would you use a compressor equipped with automatic unloaders?
a) increase capacity on demand
b) decrease capacity on demand
c) vary system capacity on demand
d) never use automatic unloaders
C
What two metals used in refrigeration work can cause electrolysis?
a) copper and brass
b) brass and steel
c) steel and nickel
d) copper and steel
D
The body if a gas charged TXV should be placed in a ______ location than the actual sensing bulb
a) warmer
b) colder
a)
Liquid line solenoid as used on an air conditioning system is there to prevent
a) liquid slugging during start up
b) liquid flooding during run cycle
c) flash gas
d) damage to compressor
a
If two capacitors were connected in series each having a 150mfd what would be the final mfd reading?
a) 300
b) 150
c) 100
d) 75
D
Silfos and other brazing materials used on freon pipe joints, their melting points range between?
a) 1100-1200
b) 1100-1300
c) 900-1200
d) 1100 -1400
D
A staged compression system is normally used when reciprocating compression ratios exceed
a) 12:1
b) 10:1
c) 20:1
d) none of the above
B
Refrigeration piping containing r717 must be colour coded and identified as per direction of flow. What colour coding is used?
a) green
b) blue
c) yellow
d) white
C
Why do some evap press regulators when used with ammonia have two temp settings?
a) when one EPR will not work
b) if coil temp is less then -10f
c) needed when holding more than one evap temp off the same suction
d) needs when attempting to hold more than one evap temp off same liquid
C
In ammonia refrigeration, where is the liquid recirculation pump located?
a) between lowP receiver and evap
b) between highP receiver and condenser
c) between lowP receiver and suction accumulator
d) there is no liquid recirculation pump
A
On new installations using the high vacuum method of evacuation, what should the micron reading be to indicate complete evacuation?
a) 100-500 microns
b) 100-200 microns
c) 50-100 microns
d) 0-50 microns
A
What combo of gas should never be used for purging or pressure checking a refrigeration system?
a) oxygen/nitrogen
b) oxygen/propane
c) nitrogen/acetylene
d) all of the above
d
In an operating AC system the air mover is a forward curve fan. If static pressure in the duct decreases, what effect does this have on the forward curved fan?
a) no effect
b) actual bhp decrease
c) actual bhp increases
d) fan will overload
B
the identified run terminal on a run capacitor must always be connected to the
a) load side of circuit
b) line side of circuit
c) directly to the start winding of the load circuit
d) to the common terminal of the split phase motor
B
A water cooled condenser has an inlet water temp of 85F and an outlet water temp of 87F. You conclude
a) system is good
b) water reg replaced
c) condenser is scaled
d) water pressure low and must be correct
C
If a refrigeration system is low on oil as well as low on refrigerant which would you add first?
a) oil
b) refrigerant
c) does not matter
B
What should an ac system have if it is equipped with face and bypass dampers?
a) two ducts
b) two coils
c) capacity control on compressors
d) capacity control on dampers
C
Refrigeration reciprocating compressors if equipped with cylinder unloaders are normally controlled by
a) discharge gas
b) condenser pressure
c) oil pressure
d) suction pressure
D
What is the purpose of having water jackets around heads of ammonia compressors?
a) keeps head cool an prevent vapor locks
b) keep heads cool and prevent condensation from forming
c) keep heads cool and prevent carbonizing around compressor heads
C
A class T machinery room shall be equipped with emergency remote control to stop the compressor in case of emergency. Control shall be located
a) outside or inside building served
b) inside or outside building served as long as its not in the equipment room
c) inside equipment room so people can shut down quickly
d) does not matter
B
All pressure relief valves for refrigeration pressure relief devices or vessels shall be set, sealed, and marked by
a) installer
b) manufacturer
c) wholesaler
d) service tech
B
Refrigerant stored in machinery rooms shall not exceed ____ of total charge of system
a) 10%
b) 20%
c) 30%
d) 40%
B
Purpose of an auto transformer as used with refrigeration or air conditioning motors?
a) decreases current draw during run
b) rectifies voltage to increase eff
c) reduces motor starting current
d) varies voltage to load conditions
D
What must be installed in a hot gas riser if its height exceeds 8ft?
a) trap
b) discharge loop
c) oil separator
d) liquid trap
A
Pressure drops in liquid lines are normally equivalent to
a) 1f
b) 2f
c) 3f
d) 4f
D
Refrigerant piping running through public hallway 7/8 line. What is minimum height allowed and how many pipe supports are required?
a) min 7.5ft every 8ft
b) min 7.5ft every 8.5ft
c) min 7.5ft every 6ft
C
A refrigeration system compressor is equipped with unloaders located 20ft above the evaporator. How should the suction line be designed?
a) suction riser
b) double suction riser
c) double trap for oil return
d) none
B
To ensure oil return to compressor, what is the minimum hot gas velocity for vertical risers?
a) 1200fpm
b) 1000fpm
c) 1400fpm
d) 500fpm
B
When is the dew point temperature of the ambient air reached?
a) dry bulb temp and relative humidity are the same
b) RH is 100% and dry bulb is below dew
c) when wet bulb sand dry bulb are same
d) none of the above
C
An averaging temperature element used to sense duct temperature in an AC system allows for?
a) hot and cold variations in room temp
b) stratification of air within the duct
c) stratification of room air
d) none of the above
B
When multiple evaporators installed below common suction line, outlet of each evap should enter the suction line
a) through an inverted loop at top of header
b) through inverted loop at bottom
c) directly in to prevent pressure drop
A
What oil viscosity would you use for low temperature ammonia systems?
a) 300ssu
b) 300multi grade
c) 150ssu
d) does not matter
B
When installing equipment to a power of 220/3/60, how many fuses should be installed and where?
a) two fuses one on each leg, in fuse box
b) three fuses one on each of the two legs and one on neutral
c) 3 fuses one on each leg, located in disconnect
c
What would cause liquid line solenoid chattering?
a) excessive liquid line pressure drops
b) low liquid line velocities
c) excessive liquid line velocity
d) liquid line not secure
C
What if liquid line solenoid fails to operate on pump down system?
a) system would operate in lower than normal temp
b) system would operate in higher than normal temp
c) not come on
d) not shut off
C
What is the best way to prevent refrigeration migration to compressor during the off cycle?
a) install liquid receiver
b) install liquid solenoid
c) install crankcase heater
d) place compressor in colder spot than condenser
C
Best method to prevent liquid flooding to compressor during run cycle using HCFC refrigerants?
a) heat exchanger
b) install suction line acumulator
C
Standard pressure setting for a walk in cooler?
a) 12psig cut out & 35psig cut in
b) 16psig cut out and 38psig cut in
c) 12psig cut out and 32psig cut in
d) 18psig cut out and 36psig cut in
D
When sizing conductors for load circuits (inductive) the wire size for an electric motor with a service factor of 115, must be
a) 110% above load amperage
b) 125% above full load circuit
c) 115% of rated load of circuit
d) at least 225% of rated load current
B
Low voltage contacts on a cooling thermostat are
a) series with cooling anticipator
b) parallel with cooling anticipator
c) no such thing as cooling anticipator
B
Rating of line transformers is very critical and should new er be exceeded. What formula for finding the correct rating of such a transformer?
a) volts x amps
b) volts x amps x 1.2
c) volts x amps x .707
d) volts x amps x pf
A
Setting of a high pressure switch to protect compressor against excessive discharge pressures is set at
a) 125% of normal operating pressure
b) 120% normal operating pressure
c) depends on type of freon
d) depends on type of condenser
e) both c and d
E
Three way valve used in conjunction with a cooling tower for condensate water would have which of the following
a) 1 inlet 2 outlet
b) 1 inlet 1 outlet
c) 2 inlets 1 outlet
d) none you would not use it
A
On a pressure enthalpy diagram, what can be found to the right of the saturated vapour curve?
a) sub cooled liquid
b) superheated vapour
c) saturated liquid
d) sub cooled vapor
B
R12 should be dried below ______ to ensure the system is free of moisture contamination
a) 10ppm
b) 13psig
c) 13ppm
d) 15ppm
D
function of a run cap is to
a) increase motor eff
b) increase power factor
c) create high torque
d) none
A
A 230v PSC comp tries to start at 184v and trips on overload protection. Starting torque is
a) not affected by voltage
b) increased by lower voltage
c) decreased by low voltage
d) dependant upon start cap used
C
Coil of a potential start relay should be as follows
a) between c and s
b) between c and r
c) between r and s
d) across 11 and 12
A
Tolerance for capacitance of a start cap generally specified by compressor manufacturer is
a) equal to or plus 20%
b) plus or minus 5%
c) minus 5% or plus 25%
d) no tolerance
A
Compressor failures are often blamed on flooding. which of the following can cause flooding
a) oversized expansion valve
b) burn out crankcase heater
c) short cycling
d) restricted capillary
A
Function of a lockout relay as used in refrigeration control circuits
a) allow system to equalize before restarting
b) prevent compressor from cycling on protection devices
d) de-energize compressor when there is a problem w system
D
What would indicate slugging?
a) high head
b) noisy comp
c) foaming in liquid line
d) noisy comp on start up
D
What would cause compressor overheating if your gauges showed a low discharge and high suction pressure
a) blown head gasket
b) overcharge
c) undercharge
d) non-condensables
A
Common description of a compressor failure is that a burn out has occurred. Which of these is your understanding of the term?
a) compressor has overheated
b) trips overload
c) motor is grounded
d) compressor fails to start
C
BBest vacuum indication
a) 29.82 “hg vac
b) 1,000 microns
c) 1lb abs
B
How to check system for non condensables?
a) temp and press of evap
b) temp and press of discharge
c) temp and press of condenser
d) none
C
Capacitance in series __________ the microfarad rating of the capacitors and __________ the total voltage that may be applied
a) reduces and increases
b) reduces and decreases
c) increases and increases
d) increases and reduces
A
What prevents cold air from escaping in an open refrigeration display case?
a) cold air is heavier thus it can’t escape
b) installation of doors
c) air curtains
d) diffusers
C
Most modern condenser operate on two types of condensing mediums; water and air. What is the normal sub-cooling provided by water cooled condensers?
a) 10 degrees
b) 30 degrees
c) 25 degrees
d) 20 degrees
D
Air flow across AC cooling coils is normally ______ cfm per ton if used for straight cooling
a) 100
b) 200
c) 300
d) 400
400cfm
Water temp when used for hot water defrost systems should be a minimum of ________ degreesf
a) 45
b) 55
c) 60
d) 60
C
Proper receiver size for the following conditions: 100lb
a) 133lb
b) 110lb
c) 120lb
d) none of the above
none of the above
In a lithium bromide and water absorption system, what liquid would be considered to be the absorbent?
a) lithium bromide
b) water
c) nitrogen
A
Crystallization in absorption systems is of great concern and normally occurs at temperatures below or at
a) 120f
b) 110f
c) 100f
d) 90f
B
If one phase of a 3 phase motor fails, which describes how the motor will operate?
a) the motor will generally not start
b) remaining two phases will draw one and one half times more current
c) windings will run hotter
d) all of the above
D
Overheating can limit the life of a compressor or cause breakdown. Which of the following can cause overheating?
a) high compression ratios
b) refrigerant floodback
c) low suction pressure
d) low compression ratios
A
What is the surest way to recognize you have contaminants in the system?
a) check head pressures
b) sight glass
c) oil sample
d) check liquid line filter drier
C
Best trap for system contaminants as a result of compressor burnout is a
a) suction line filter
b) liquid line filter
c) condenser
d) evaporator
A
Which desiccant has the best ability to remove acids in a refrigeration system?
a) methyl alcohol
b) activated alumina
c) molecular sieve
d) desiccants do not remove acids
B
Normal temperature drop through a chiller is
a) 2f with flow of 10-20gpm/ton
b) 10f with flow of 10-15gpm/ton
c) 2f with flow of 10-15gpm/ton
d) 2f with flow of 130-150gpm/ton
C
Pneumatic energy sources normally supply air to the controllers at a regulated supply pressure of
a) 15-25psig
b) 20-25psig
c) 80psig
d) none of the above
A
