FDNY written z51 Exam Questions Marking Scheme Current Update 2024-2025. Questions & Ans, Exams of Refrigeration and Air Conditioning

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FDNY written z51 Exam Questions Marking Scheme

Current Update 2024-2025. Questions and Correct

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A Centrifugal compressor is in operation with suction pressure is 3 psig and the discharge is 10 psi what is the atmospheric pressure 14.7 which is the ratio to: - ANS1. A centrifugal water pump is considered to be fully primed when - ANSThe pump is full of liquid A centrifugal water pump is known as a lift pump when the: - ANSThe water supply to the pump suction inlet is below the pump level A chill water system uses refrigerant R134 a leak in the evaporator shell may result in: - ANSSet off the refrigerant monitor alarm A chilled water system has an air cooled condensing unit on a roof during cold weather ha what type of protection? - ANSAir limiting device A circuit breaker has a similar function as what? - ANSA fuse A condenser pump is supplied with 85 degree water from a cooling tower and returns to the tower at 88 degrees engineer is sure the condenser tubes are clean and free of obstructions. the condenser has high condenser pressure. the reason for this could be? - ANSOver charge of refrigerant

A facility has failed to maintain water treatement to a refrigerant system: - ANSIncrease in the condenser pressure A FDNY permit is required to conduct hot works for? - ANSUse of oxygen and flammable gas A high-side float valve is used to maintain: - ANSConstant level of refrigerant in the evaporator A low side float valve is used to maintain: - ANSThe level of the refrigerant in the evaporator A motor winding is touching the inside of the motor housing. this could result in: - ANSShock may occur to personnel A multi-cylinder reciprocating compressor uses cylinder unloaders to regulate capacity, what would not occur if some of the unloaders fail to operate when needed? - ANSThe chill water temperature will increase A reciprocating compressor cylinder has a 10 inch bore and 14 inches stroke. the volume of refrigerant, in a cubic inches, will be closer to: - ANS A reciprocating compressor is making a knocking sound during operation. if the refrigerant worn parts are not causing the knocking, what is probably the cause - ANSThe slugging of the liquid refrigerant

A refrigerant engineer verifies that a chilled water pump is cavitating. of the following the most likely cause for this condition is: - ANSWater leaks through the mechanical seals A refrigerant engineer verifies that a condenser water pump is cavitating. of the following the most likely cause for this condition is: - ANSA faulty cooling tower water level controller A refrigerant engineers was instructed to charge of 60 ton plant with R134A refrigerant. the refrigerant engineer will most likely find the charging valve on the

• ANSLow pressure side of the system A refrigeration compressor has failed to turn on. the refrigeration engineer on duty verifies that the electrical circuit to the motor, including all switches and circuit breakers, is complete according to recommended service practice, the next item to be checked would likely be the: - ANSTemperature and pressure controls A refrigeration engineer is logging reading from a reciprocating system. compressor discharge temperature have dropped significantly and the suction line pressure is high. which of the following that may be causing this set of condition. - ANSAn expansion valve that is open to wide A refrigeration engineer is running two centrifugal condenser water pumps in parallel. one of the pumps is a maximum pumping rate. if by mistake, the refrigeration engineer throttles back on the discharge valve of the other pump, the most likely effect will be: - ANSA reduction on the total flow rate to the condenser

A refrigeration engineer notices excessive cycling of the temperature control for a reciprocating compressor refrigeration unit. the crankcase temperature is high, the compressor discharge temperature low, the suction line temperature high. of the following the one that may causing this set condition. - ANSFaulty compressor valves A refrigeration system uses jet ejector to raise settled oil mixed with refrigerant to the oil pump if a restriction in the refrigerant flow to the jet ejector develops: - ANSThere may be insufficient head to lift the oil A rooftop water cooling tower is connected to a water pump in the building basement with a 12 inches diameter pipe. with the pump turn off, a pressure gauge at the pumps inlet show a pressure of 140 PSIG the height of the water column, in feet, would be closet to. - ANS A single phase 208 VAC circuit has 2 hot wires and the third is? - ANSGround A solenoid valve is used to allow a reciprocating refrigeration machine to adapt to the load on the system. the opening of the solenoid valve is caused by: - ANSAn electrical current creating a magnetic field A standpipe system will be out of service for two days. how long should there be a fire watch? - ANSThe entire time the standpipe is out of service A super heated vapor is a? - ANSDry vapor above the saturation temperature A system controlled by a TXV show high discharge pressure and high normal sub- cooling. the cause is most probably a : - ANSRefrigerant overcharge

A technician had been asked to estimate the cost of operating a 5 horse power motor. because the plant is build by energy consumed as kiliowatt-hours, the technician will have to calculate the conversion. the equivalent in energy of a 5 horse power motor operating for 9 hours in kiliowatt-hours is closest to: - ANS33. A TXV is used to maintain constant: - ANSEvaporator superheat A water chiller is equipped with a reciprocating compressor, a thermostatic expansion valve and an air cooled condenser. a restriction in the refrigerant liquid line would result in: - ANSHigh suction superheat A water chilling system uses refrigerant R123. a leak in the evaporator shell mat result in - ANSA higher than normal high side pressure A water pump is discharge against head 92 feet of water, this is approximately to a pressure of: - ANS40 psi According to the attached Material Safety Data Sheet (MSDS) R134 is a - ANSClear, odorless liquid and vapor After recovering liquid refrigerant from a centrifugal chiller the next step is to? - ANSRecover vapor All liquid has been recovered from a system to be overhauled, the system - ANSShould not be opened until all vapor has been removed

An automatic expansion valve maintains a constant: - ANSEvaporator pressure An electrically operated control requires 24 volts to operate. to change the available 110 volts to 24 volts - ANSTransformer An engineer is requested to replace a gauge on the high side of the system. the pressure graduation rate should be: - ANSAt least 1.2 times the design pressure An engineer needs to vary the flow of refrigerant in a refrigeration system. which operation in the flow of the system does not include: - ANSSolenoid valve An engineer observes a gauge that reads saturation pressure of a refrigerant. if chilled water s circulate as the cooling medium this reading best be used to estimate the? - ANSTemperature of chilled water being pumped to the space being cooled An engineer suspects a short of the motor winding's have caused the motor to trip on overload. the engineer should use what instrument to check the motor: - ANSOhmmeter An engineer would expect a relief valve to start function at a pressure: - ANSDesign pressure An equalizer line on a TXV is used to: - ANSCompensate for the pressure drop across the evaporator coil

An indirect ow temperature refrigerant system frequently uses glycol , instead of salt brine, as the intermediate cooling medium. an advantage of this choice is: - ANSThe elimination of corrosion As an engineer you notice pressure drops across the evaporator. you check and notice the external equalizer line is disconnected. what will occur in the evaporator? - ANSEvaporator will flood As shown in the picture below, the suction gauge of a condenser water pump reads 55 PSI. the pipe supplying the pump is 75 feet long and 12 inches in diameter. approximately how many gallons of water do you expect to obtain if this pipe is drained completely? - ANS Assume that a refrigeration engineer has a choice of four valves to select from. which of the following is the most effective type of valve to control pressure? - ANSPlug valve Assume that an engineer is able to observe refrigerant water and oil together. the fluids would settle in the container from top to bottom: - ANSOil, water, refrigerant Capacitors are used on refrigeration motors. of the following, the function of these devices is to? - ANSStore electrical charges during starting and running the motor Capacity control of a reciprocating hermetic compressor is typically achieved through - ANSOperation of the hot gas bypass valve

Centrifugal pressure is determined by? - ANSSpeed of motor Cooling tower water requires the addition of chemical additives in order to: - ANSReduce the formation of scale and algae Copper and aluminum are frequently used for condenser tubes in refrigeration system. these metals are used because of their: - ANSHigh heat transfer coefficient Copper tubing refrigerant lines must be installed for a new system. it is a well known service practice that tubing collapses at bends that must be made, the refrigerant engineer should use - ANSLever type tubing bender Cross connections and standpipe risers must be painted: - ANSRed During inspection of a facility you notice that there has been a failure to maintain water treatment of the condenser water. the first evidence of a problem would be: - ANSAn increase in compressor head pressure Electric devices may be used to provide built in defrosting of refrigeration machine evaporator units. these devices are classified as - ANSResistors Electrical current is measured in? - ANSAmperage FDNY is most concerned with which ASHRAE refrigerant classification? - ANSA Filter driers remove - ANSMoisture and particles

Fireproof decorations n buildings is useful for? - ANSDon't catch fire in an emergency Fusible plugs on a condenser: - ANSThe melting point is marked on it How do you start a centrifugal chiller? - ANSStart the chilled water pump, start the condenser water pump, check oil, start cooling tower, start compressor How long does it take to warm up a steam turbine? - ANS10-15 minutes How long must a fire alarm log book be kept? - ANS3 years How many BTU's are removed in a 30 ton system: - ANS360,000 BTU's per hour How much extra refrigerant can be stored in a machine room? - ANS330 lbs. How often must you do an emergency power testing? - ANSMonthly How would you calibrate a thermometer? - ANSPlace the thermometer in a cup of ice water How would you put an additional pump online? - ANSOpen suction valve, open discharge valve gradually

IF 29.92'HG is equal to 14.7 Psia then 26"HG converts to what in Psia? - ANS12. If a sprinkler system is offline for two days how often do you need to inspect it until it is returned back to service? - ANSContinuously 24 hours a day until system is restored If R134 accidentally touches a refrigerant engineer's skin, what first aid should be applied from the MSDS? - ANSPromptly flush skin with water until all chemical is removed If resistance is cut in half, what happens to the power factor? - ANSIncreases by a factor of two If the air louvers below the fans in an induced draft cooling tower become clogged the result would be: - ANSHigher return water temperature In a multi stage centrifugal compressor, each stage: - ANSIs identical in volume to the other stages In a steam turbine, what is the function of the kingsbury thrust bearing - ANSMaintain axial positioning of the rotor shaft In an indirect refrigerant system, of the following , the one that would not be used as a cooling medium for the building spaces being cooled is: - ANSR22 refrigerant In building with a multizone standpipe system, how does each zone get supplied with water? - ANSEach zone will have its own automatic water supply

In most semi hermetic compressors, the suction vapor is used to: - ANSCool the motor In order for a refrigerant to become superheated in a section of the lowside refrigerant line: - ANSWhere no liquid refrigerant is present In relation to the suction pressure of a compressor, the reading on the oil pressure gauge should read in the range, closer to: - ANS15 to 30 PSI Higher In the absence of water chemical treatment of a cooling tower? - ANSDrain tower every one to two weeks & replace with fresh water In the picture below describe the equipment's function? - ANSRemove non condensable from the condenser In the picture below what does the equipment detect? - ANSRefrigerant leaks In the picture the valve is in what position (45 degree angle to the left) - ANSThe valve is crack open Information about the physical and chemical properties of a hazardous material can be found in: - ANSMaterial Safety Data Sheet Liquid level gauge glasses (except the bull's eye) are generally equipped with: - ANSAutomatic shut-off valves only

Liquid refrigerant that has passed through a meter device is a? - ANSLow pressure saturated liquid Manifold hoses should be equipped with? - ANSLow loss fittings Modern compressors usually seal the rotating shaft as it exits the compressor housing a spring loaded seal made of - ANSMetal or carbon Non- condensable gases like air, oil vapor, or nitrogen travel through a refrigerant system with the refrigerant they usually accumulate in the: - ANSCondenser Of the following centrifugal chillers are best characterized as? - ANSHigh tonnage, low pressure machines Of the following, and example of an in-line refrigerant cleaning system that may be used with a centrifugal compressor containing R123 refrigerant is: - ANSRefrigerant recycling Of the following, centrifugal refrigerant machine is best characterized by: - ANSHigh volume low pressure machine Of the following, the major advantage of a shell and coil condenser is: - ANSThere is less dangers of developing leaks Of the following, the most common metering device used today in reciprocating commercial refrigeration system under three tons capacity is: - ANSTEV

Of the following, the statement that most accurately characterize a hermetic compressor is that it: - ANSWill have both the compressor and motor enclosed is gas tight housing On a steam turbine, what would cause the atmospheric valve to open? - ANSlow vacuum in the surface condenser, leaking tubes in the surface condenser, dirty tubes n the surface condenser On an operating centrifugal compressor refrigerant unit, the refrigeration engineer notices that the compressor is short cycling. the unit is using low side float valve as a metering device. of the following requirements this would indicate that: - ANSThe system is undercharged with refrigerant On what characteristics is ASHRAE refrigerant safety group classification system: - ANSFlammability and toxicity Picture of compressor: - ANSOil charging port allows for the addition and removal of oil from the compressor Picture of pump: - ANSNinety degree reducing elbow, pump suction, pump casing, pump discharge, check valve Refrigerants are characterized by their physical properties included flash point, refrigeration effect, and others. of the refrigerant in commercial and industrial the highest latent hear and refrigerant effect is: - ANSAmmonia Regarding fire safety, which ASHARE refrigerant safety classification indicates no flammability and lower the toxicity? - ANSA

Regarding the functioning of a steam turbine, why is it advisable to keep moisture in the inlet low as possible? - ANSKeeps turbine blades wear to minimum Regarding the functioning of steam turbine, how is the water level controlled in the surface condenser hot well? - ANSOperation of the recirculation and overboard valves Regardless of the ASHRAE refrigerant classification in use, in the event of a refrigerant escape the engineer should be aware of? - ANSAsphyxiation Show a picture of an insulated pump and ask what is this pump? - ANSCentrifugal chill water pump Stand pipe certificate should be available for? - ANSFDNY and building inspector The advantage of forced draft cooling tower over natural draft cooling tower is: - ANSSmaller tower size The amount of electrical power used to operate a solenoid valve or a motor is measured in: - ANSVolts The amount of refrigerant that flows through the orifices of a economizer is determined by the: - ANSDifference between the high side and load side pressure

The British Thermal Unit (BTU) is the measurement of heat of energy. if 10 BTU are transferred to 10 pounds of water, the water temperature increase will be closest to: - ANS1F The cause of a starved evaporator might be: - ANSLow refrigerant charge The charge in a TEV sensing bulb is? - ANSSimilar to refrigerant in system The chilled water supply to the building is 55F. if the chiller is being used for human comfort, should you be concerned about this , and why? - ANSYes, this temperature is too high for human comfort purpose The condenser pump is on the first floor and not running. the pressure gauge shows 55 psi. there is 15 feet for each floor. what floor is the cooling tower on? - ANS The cooling medium for a cooling tower is? - ANSAir The cooling medium for an evaporative condenser is: - ANSAir and water The efficiency of the refrigerant cycle is affected by the operation of the condenser. of the following. a more efficient centrifugal compressor operation results from: - ANSLowering the condensing pressure The flash point of compressor lubricating oil: - ANSShould be higher than the compression temperature

The following is a desirable property in a refrigeration - ANSHigh latent heat The heat removed from the refrigerant in a condenser is: - ANSSensible and latent heat The installation of an inline refrigerant cleaning system is advisable: - ANSTo remove impurities from the system The most important reason for installing a muffler in a reciprocating refrigerant machine is: - ANSTo contain the compressor pulsation noise The most important reason to sub-cool the refrigerant in the condenser is to ensure that: - ANSA pure liquid refrigerant will enter the metering device The most important reason to use at least two compressors in a cascade system is to: - ANSAvoid very high compression ratio for each compressor The most important requirements for a good evaporator is that: - ANSIt must have enough cooling surface to absorb the required heat The most likely reason for a refrigeration engineer to use a psychrometer is to measure - ANSRelative humidity level of the atmosphere The oil collected in an oil separator is generally: - ANSReturned to the compressor

The only refrigerant/ temperature chart available to a refrigerant engineer list the temperature is degrees Celsius if the chart indicates a Celsius temperature of 4 degrees to equivalent to F: - ANS39.2 degrees The only refrigerant/temperature chart available to a refrigerant engineer lists the temperature in degrees Celsius. if the chart indicates a Celsius temperature of 5 degrees the equivalent in Fahrenheit is? - ANS41 degrees The packing gland of a centrifugal pump serves to: - ANSThe drip part of the packing gland gives evidence that there is water in the pump The primary way of achieving capacity control of a centrifugal compressor is by; - ANSAdjustment of the impeller inlet pre-rotation vanes The process by which refrigerant is extracted and cleaned for reuse without requirements for reclamation is called - ANSRecycle The purpose of wear rings in a centrifugal pump is to: - ANSPrevent wearing of the pump housing and impeller The ratio of the actual pressure of water vapor in the atmosphere to the saturated pressure of give temperature is: - ANSRelative humidity The refrigerant unit that you have been assigned to is being taken out of service for a major repair. you have been assigned to withdraw refrigerant for storage in suitable containers. according to the new York city fire code, you must ensure that the containers: - ANSAre approved by the US department of transportation

The rupture disc for a low-pressure centrifugal refrigeration machine is normally located on the: - ANSCompressor suction The sole refrigeration engineer on duty in a building is permitted to leave the building refrigeration system when it is in operation when: - ANSRelieved by another licensed refrigeration engineer The suction and discharge valve of the reciprocating compressor are mounted as follows: - ANSDischarge valves on top of the valve plate and suction valve below The suction pressure of a reciprocating compressor is 65PSIG. the discharge pressure of this compressor is 120PSIG. the atmospheric is 14.7 PSI. the compression ratio for the given condition is closet to: - ANS1. The suction service valve of a reciprocating compressor is front seated and the compressor runs until the low pressure cut-out shut the compressor off. when the machine is stopped, the refrigeration engineer notices that the suction pressure increase rapidly. the most probable cause of this pressure rise: - ANSMalfunction of a compressor valve The total amount of heat to be removed from the refrigerant in a condenser equals the heat picked up in the: - ANSEvaporator plus the heat of compression The type of refrigerant system that is least likely to leak refrigerant into the building space that are cooled - ANSThe indirect system The use of oil in the refrigeration machine is to: - ANSReduce wear and friction in the compressor parts

The vessel depicted below may used in connection with - ANSRefrigerant recovery the viscosity of lubrication oil is described by a number. a low viscosity number describes oil that: - ANSFlows easily There is 7.48 gallons per cubic foot. how many gallons of water are in a pipe 8 feet in diameter and 10 feet long? - ANS There is a decrease in the efficiency of a reciprocating compressor. this most likely caused by: - ANSLeaking suction valve thermal bulb is attached to the suction pipe between the evaporator coil and the compressor by an insulated line. assume that the machinery room is at 85F. break down of the insulation results in: - ANSFlood the evaporator To convert water 32F to ice at the same temperature a refrigeration system must remove: - ANSThe latent heat of fusion Under certain circumstances is it ok to chain an exit door? - ANSNo, its never ok Under normal condition, the refrigerant enters the compressor as a: - ANSLow pressure superheated vapor and leaves as a high pressure vapor Water and moisture is serious problem in a refrigerant system how to avoid: - ANSProper evacuation at the charging of the system

Water regulating valves are used to? - ANSMaintain condenser pressure to pre- determined level What are pre hot works procedures performed prior to hot works? - ANSCheck area once a day leading up to hot works What are steam ejector used for on the surface condenser of a system with a turbine: - ANSTo create a proper opening exhaust system what device automatically controls the speed of a turbine? - ANSGovernor valve What device protects the steam turbine from excessive speed? - ANSgovernor assembly What does a wiring diagram display? - ANSWiring of components What happens when a steam turbine reaches critical speed? - ANSTurbine will vibrate violently What information is not contained in a material safety data sheet-MSDS? - ANSCost of material What is a compressor safety head? - ANSA spring on the valve plate What is ammonia's refrigerant ASHRAE classification? - ANSB

What is most accurate about fire alarm books? - ANSMust be kept in the fire alarm panel What is not required to be serviced annually? - ANSCompressors What is the advantage of a shell and tube condenser, as opposed to a shell and coil condenser? - ANSBetter heat transfer What is the device used to measure the speed of a turbine? - ANSTachometer What is the function of a safety head on a compressor? - ANSPrevents liquid slugging from damaging the valve plate What is the function of the gland steam? - ANSSeal the turbine rotor carbon rings What is the function of the turbine auxiliary oil pump? - ANSEstablish oil pressure during turbine start up What is the function of the vacuum breaker in a steam turbine. - ANSTo achieve a faster coast down cycle What is the lowest temperature a cooling tower can be? - ANSWet bulb temperature What is the minimum requirement an engineer needs to log readings? - ANSOnce per shift

What is the most widely used regulation book by operating engineers is? - ANSEPA What is the order of components on the liquid line of a reciprocating system from the condenser to the TEV? - ANSKing valve, filter drier, solenoid valve, sight glass What is the primary reason ribbed metal piping is used for electrical wires connected to the refrigeration system shown below? - ANSIt allows for flexibility and accounts for vibrations What is the responsibility of a B29 COF holder? - ANSInspect the battery system What is the state of refrigerant entering the compressor on a reciprocating machine? - ANSSuperheated vapor What is the volume of a box 12" x12" x12" measure? - ANS1 cubic foot What is used on an outside pipe to prevent it from freezing? - ANSResistor What type of refrigerant do you need FDNY approval for? - ANSPropane What type of refrigerant is found inside the machines Gauges? - ANSSame type of refrigerant inside the machine What type of sprinkler system needs inspecting? - ANSAutomatic

When a refrigerant engineer uses a portable compressor recovery unit to remove vapor refrigerant from a refrigeration system the removal rate of the refrigerant will gradually slow down because - ANSThe vapor density is decreasing When an expansion valve is operating properly, at the end of the evaporator will contain: - ANSOnly superheated vapor When charging refrigerant on the low side of a reciprocating machine with manifold gauges, what is the position of the manifold? - ANSHigh side frontseated low side backseated When entering phase 2 fireman's service, what statement is correct? - ANSThe elevator operator is the only person that could control the elevator When is a chemical fire extinguisher system needed? - ANSWhere water is not sufficient When will the BTU's exchanged be the greatest? - ANSlow evaporator temperature, high condenser temperature When you finished leak testing with R22 and nitrogen the next step should be? - ANSVent refrigerant and nitrogen to open air Where is emergency power not required according to code? - ANSData centers Where is the muffler located? - ANSBetween the compressor and the condenser

Where must the material safety data sheet be located? - ANSWhere available to all employees Which of the following ASHRAE refrigerant safety classification is the most flammable? - ANSA3 Which of the following best describes how the cylinder unloader work? - ANSKeep in the suction valve opened while the compressor is in the return stroke Which of the following correctly describes the object in the picture below? - ANSStandpipe hose outlet to put out fires in cae of emergency Which of the following does not require flame resistant treatment? - ANSART work in a museum Which of the following is a correct statement? - ANS2.5 gallons of water weighs 20.8 pounds Which of the following will connect to the middle port on a gauge manifold? - ANSVacuum pump Which of these compressors is not a positive displacement type compressor? - ANSCentrifugal Which service valve should be installed to isolate a dual pressure relief valve while keeping system in service? - ANSThree way valve

While doing a routine line inspection, the engineer notices the bulb of the TXV on the floor refrigerant engineer should attach bulb at the : - ANSThe outlet end of the coil While on duty a refrigeration engineer notice that the suction line to the compressor and part of the compressor itself is frosted of the following, the most likely reason for this condition would be: - ANSThere is not enough refrigerant in the system While operating an R-22 single acting compressor system, the refrigeration engineer noticed oil foaming in the crankcase. this condition most likely, would have been caused by a : - ANSSudden drop in the crankcase pressure Why is a pressure relief valve better that a fusible plug? - ANSMinimizes refrigerant loss Why is refrigerant gauge called a compound gauge? - ANSIt reads positive pressure and vacuum With a 75 degree dry bulb and a 73 degree wet bulb the relative humidity is? - ANSVery high You are performing hot works near a sprinkler head. what can you do to prevent the fire alarm from going off? - ANSTake the building offline You are the engineer running a 2000 ton steam-driven turbine centrifugal refrigeration system, a refrigeration system supplies chilled water to a college campus with multiple buildings. you are supplying 46 degree chilled water. all the