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RETA CIRO practice questions

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Question 1Industrial Refrigeration I

In a vapor-compression refrigeration system, heat is absorbed from the refrigerated space in the:

  1. compressor
  2. receiver
  3. condenser
  4. evaporator Correct answer.

Explanation

The evaporator is the heat exchanger in which low-pressure liquid refrigerant boils and absorbs heat from the space or product being cooled.

Question 2Industrial Refrigeration I

The primary function of the compressor in a refrigeration system is to:

  1. separate oil from the discharge gas
  2. meter liquid refrigerant to the evaporator
  3. raise vapor pressure for condensing Correct answer.
  4. remove heat from the refrigerant vapor

Explanation

The compressor raises the pressure and temperature of the vapor so it can be condensed by the available cooling medium at the condenser.

Question 3Industrial Refrigeration I

The component that reduces refrigerant pressure from condensing pressure to evaporating pressure is the:

  1. condenser
  2. expansion valve Correct answer.
  3. compressor
  4. receiver

Explanation

The expansion device throttles refrigerant from condensing pressure down to evaporating pressure and separates the high side from the low side.

Question 4Industrial Refrigeration I

Anhydrous ammonia vapor is ______ air at the same temperature.

  1. heavier than
  2. the same density as
  3. lighter than Correct answer.
  4. about twice as dense as

Explanation

Ammonia vapor is roughly 0.6 times as dense as air, so it rises and tends to collect at ceilings and high points.

Question 5Industrial Refrigeration I

The IDLH concentration for anhydrous ammonia is approximately:

  1. 3,000 ppm
  2. 30 ppm
  3. 300 ppm Correct answer.
  4. 50 ppm

Explanation

The IDLH for ammonia is 300 ppm, a level at which a worker could be overcome and unable to escape without respiratory protection.

Question 6Industrial Refrigeration I

The primary purpose of a high-pressure receiver in an ammonia system is to:

  1. store liquid and seal the condenser drain Correct answer.
  2. separate noncondensable gases from the discharge
  3. cool the liquid below condensing temperature
  4. remove moisture from the refrigerant

Explanation

The high-pressure receiver stores liquid refrigerant and provides a liquid seal so that vapor cannot back up into the condenser drain.

Question 7Industrial Refrigeration I

Before maintenance work begins on a refrigeration compressor, the accepted practice is to:

  1. notify the shift supervisor and proceed
  2. close the suction valve only
  3. reduce suction pressure to zero and start work
  4. lock out, tag out, and verify isolation Correct answer.

Explanation

Energy isolation with lockout/tagout plus verification of zero energy is required before anyone is exposed to moving parts, pressure, or electrical energy.

Question 8Industrial Refrigeration I

At saturation, the pressure and temperature of a pure refrigerant are:

  1. directly related Correct answer.
  2. independent of each other
  3. inversely related
  4. equal in value

Explanation

For a pure refrigerant at saturation, each pressure corresponds to exactly one temperature, so the two rise and fall together.

Question 9Industrial Refrigeration I

Superheat is the difference between the actual suction line temperature and the:

  1. discharge temperature at the compressor outlet
  2. ambient air temperature at the condenser
  3. saturation temperature at the suction pressure Correct answer.
  4. condensing temperature at the discharge pressure

Explanation

Superheat is the number of degrees the vapor is above the saturation temperature corresponding to the measured suction pressure.

Question 10Industrial Refrigeration I

Subcooling the liquid refrigerant before it reaches the expansion valve primarily:

  1. reduces the mass of refrigerant circulated
  2. increases the refrigeration effect Correct answer.
  3. raises the evaporating pressure
  4. increases the compressor discharge temperature

Explanation

Subcooling removes additional heat from the liquid, increasing the refrigeration effect per pound and giving the liquid margin so it does not flash before the valve.

Question 11Industrial Refrigeration I

A thermostatic expansion valve regulates refrigerant flow in response to:

  1. the compressor oil pressure
  2. the condensing pressure
  3. evaporator outlet superheat Correct answer.
  4. the liquid level in the receiver

Explanation

The TXV senses evaporator outlet temperature with its bulb and evaporator pressure, then modulates flow to hold a set amount of superheat.

Question 12Industrial Refrigeration I

In a liquid overfeed system, the recirculation rate is the ratio of:

  1. vapor formed to liquid pumped
  2. pump discharge pressure to suction pressure
  3. liquid pumped to liquid evaporated Correct answer.
  4. condenser flow to evaporator flow

Explanation

Recirculation rate, or overfeed ratio, is the mass of liquid delivered to the evaporator divided by the mass evaporated there.

Question 13Industrial Refrigeration I

Cavitation of a liquid ammonia recirculating pump is most commonly caused by:

  1. excessive subcooling of the liquid in the condenser
  2. high oil content in the refrigerant
  3. excessive discharge pressure
  4. insufficient net positive suction head Correct answer.

Explanation

The pump needs adequate NPSH; if the liquid is near saturation and suction line pressure drop is excessive, vapor forms at the pump inlet and the pump cavitates.

Question 14Industrial Refrigeration I

The purpose of an oil separator in the compressor discharge line is to:

  1. cool the discharge gas before it reaches the condenser
  2. separate noncondensable gases from the refrigerant
  3. add oil to the suction gas for compressor lubrication
  4. remove oil from the discharge gas Correct answer.

Explanation

An oil separator removes most of the oil entrained in the hot discharge gas so oil does not coat heat-transfer surfaces or collect in low points.

Question 15Industrial Refrigeration I

Hot gas defrost of an evaporator works by:

  1. raising suction pressure by opening the expansion valve
  2. shutting off refrigerant and using electric heaters
  3. piping hot discharge gas through the coil Correct answer.
  4. circulating warm brine through the coil

Explanation

In hot gas defrost, high-temperature compressor discharge gas is routed through the evaporator so the frost melts, after which the coil returns to refrigeration.

Question 16Industrial Refrigeration I

Air most commonly enters an ammonia refrigeration system when:

  1. the compressor oil is changed
  2. the condenser cooling water temperature is high
  3. the receiver level is too high
  4. the system runs below atmospheric pressure Correct answer.

Explanation

Whenever any part of the system is below atmospheric pressure, air and moisture can be drawn in through seals, packing, or openings.

Question 17Industrial Refrigeration I

The approach of a cooling tower is the difference between the:

  1. hot water and dry bulb temperatures
  2. wet bulb and dry bulb temperatures
  3. entering and leaving water temperatures
  4. cold water and wet bulb temperatures Correct answer.

Explanation

Cooling tower approach is the cold water temperature minus the entering wet bulb temperature; it shows how closely the tower reaches the wet bulb limit.

Question 18Industrial Refrigeration I

Scale buildup on an evaporative condenser coil will cause:

  1. no measurable change in performance
  2. higher condensing pressure Correct answer.
  3. higher evaporating pressure
  4. lower condensing pressure and reduced compressor power

Explanation

Scale insulates the coil and reduces heat transfer, so the compressor must run at a higher condensing pressure and consumes more power.

Question 19Industrial Refrigeration I

Reciprocating compressor cylinder unloaders reduce capacity by:

  1. reducing the compressor speed
  2. holding the suction valves open Correct answer.
  3. closing the discharge valves
  4. bypassing discharge gas to the suction line

Explanation

Unloaders hold suction valves open so the cylinder cannot compress vapor, dropping capacity in steps as cylinders are unloaded.

Question 20Industrial Refrigeration I

The liquid level in a low-pressure receiver must be kept high enough to:

  1. maintain discharge pressure
  2. prevent vapor from entering the pump Correct answer.
  3. keep the condensers flooded
  4. prevent oil from leaving the low-pressure receiver

Explanation

The low-pressure receiver must maintain a liquid seal so the pump takes liquid only; if the level falls too low, vapor enters the pump and it cavitates.

Question 21Industrial Refrigeration I

Two relief valves installed on a vessel with a three-way valve allow the operator to:

  1. set two different relieving pressures at the same time
  2. test one valve while the other stays in service Correct answer.
  3. relieve refrigerant to atmosphere during normal operation
  4. increase total relief capacity during peak load

Explanation

The three-way valve lets the operator switch the relief path to one valve, remove the other for bench testing, then switch back without pumping the vessel down.

Question 22Industrial Refrigeration I

A recirculating system pumps 4 pounds of liquid ammonia for every pound evaporated in the evaporators. The vapor fraction (quality) of the mixture leaving the evaporator is approximately:

  1. 100 percent
  2. 75 percent
  3. 25 percent Correct answer.
  4. 50 percent

Explanation

With a 4:1 recirculation rate, 4 pounds of liquid enter and 1 pound evaporates, so the vapor fraction leaving the coil is 1/4, or 25 percent.

Question 23Industrial Refrigeration I

Oil injected into a twin-screw ammonia compressor serves mainly to:

  1. prevent the rotors from turning too fast
  2. increase the compression ratio
  3. act as a refrigerant in the evaporator
  4. seal clearances and cool the rotors Correct answer.

Explanation

Injected oil seals rotor clearances, lubricates the bearings and rotors, and carries away the heat of compression so the machine can run at high pressure ratios.

Question 24Industrial Refrigeration I

An automatic air purger on an ammonia system is connected to the:

  1. bottom of the low-pressure receiver
  2. suction line at the compressor inlet
  3. liquid line at the expansion valve
  4. highest point of the condenser Correct answer.

Explanation

Noncondensable gases such as air collect at the coldest, highest point of the high side, usually the top of the condenser, which is where the purger is connected.

Question 25Industrial Refrigeration I

Increasing the clearance volume of a reciprocating compressor will:

  1. increase the mass flow of refrigerant
  2. have no effect on volumetric efficiency
  3. decrease the volumetric efficiency Correct answer.
  4. increase the volumetric efficiency

Explanation

Clearance volume holds high-pressure vapor that re-expands on the suction stroke, so a larger clearance volume reduces volumetric efficiency.

Question 26Industrial Refrigeration I

At standard atmospheric pressure, ammonia (R-717) boils at approximately:

  1. 32°F (0°C)
  2. -60°F (-51°C)
  3. -28°F (-33°C) Correct answer.
  4. 0°F (-18°C)

Explanation

The normal boiling point of a refrigerant is its saturation temperature at 14.7 psia. For ammonia this is about -28°F (-33°C), which allows low-temperature refrigeration without a deep vacuum on the low side.

Question 27Industrial Refrigeration I

The main effect of noncondensable gases accumulating in a condenser is that:

  1. The liquid line becomes subcooled
  2. The evaporating pressure falls below design
  3. The condensing pressure rises above normal Correct answer.
  4. The compressor discharge temperature falls

Explanation

Noncondensable gases such as air do not condense at normal condensing temperatures, so they blanket coil surface and add their own partial pressure. The result is a higher total condensing pressure for the same condensing temperature, which raises compressor power.

Question 28Industrial Refrigeration I

Bubbles in a liquid line sight glass most directly indicate:

  1. The condenser is flooding back to the compressor
  2. The receiver is completely full of liquid
  3. Flash gas is present in the liquid line Correct answer.
  4. The expansion valve is overfeeding the evaporator

Explanation

A sight glass shows the condition of the liquid refrigerant, and bubbles indicate vapor is present. This is normally flash gas caused by insufficient subcooling, excessive pressure drop, or a low charge.

Question 29Industrial Refrigeration I

Because ammonia vapor is lighter than air, fixed ammonia detectors should be mounted:

  1. Near the ceiling or at other high points Correct answer.
  2. At mid-height on the wall opposite the door
  3. Outside the machinery room only
  4. At floor level near drains and pits

Explanation

Ammonia vapor is roughly 0.6 times as dense as air, so a release tends to rise and collect at high points. Detectors are therefore placed near the ceiling or above likely leak sources so they sense the gas promptly.

Question 30Industrial Refrigeration I

Excessive pressure drop in a suction line will:

  1. Have no effect on capacity but increase oil carryover
  2. Lower the condensing pressure and improve efficiency
  3. Reduce capacity and raise the compression ratio Correct answer.
  4. Increase capacity and reduce discharge temperature

Explanation

The compressor sees the pressure at its suction flange, which is lower than the evaporator pressure when line loss is high. A lower suction pressure raises the compression ratio and reduces the mass flow the compressor can handle.

Question 31Industrial Refrigeration I

A minimum condensing pressure is maintained in cold weather primarily to:

  1. Prevent the compressor from running too slowly
  2. Reduce the amount of subcooling in the condenser
  3. Provide pressure drop across the expansion valve Correct answer.
  4. Keep the receiver from becoming empty

Explanation

The expansion device needs a pressure difference between the high side and low side to feed refrigerant at the required rate. Holding a minimum condensing pressure also supports hot gas defrost and reliable oil management.

Question 32Industrial Refrigeration I

A low-side float valve is used to:

  1. Hold liquid level in a flooded evaporator Correct answer.
  2. Regulate receiver pressure during low load
  3. Control superheat at the evaporator outlet
  4. Bypass hot gas during capacity reduction

Explanation

A low-side float valve senses the liquid level in a flooded evaporator or low-pressure receiver and modulates flow to hold that level. It does not use superheat as its control signal.

Question 33Industrial Refrigeration I

Operating a reciprocating compressor at an excessively high compression ratio most likely results in:

  1. Lower oil temperatures and longer oil life
  2. Higher volumetric efficiency and capacity
  3. Very high discharge temperatures Correct answer.
  4. Reduced discharge superheat at the valves

Explanation

As compression ratio rises, the heat of compression raises the discharge gas temperature. Sustained high discharge temperatures can break down oil, form carbon, and damage valves and rings.

Question 34Industrial Refrigeration I

Liquid refrigerant entering a reciprocating compressor (slugging) is harmful mainly because it:

  1. Lowers discharge pressure below the condensing pressure
  2. Increases the compressor's volumetric efficiency
  3. Can damage valves and internal parts Correct answer.
  4. Causes the oil separator to stop working

Explanation

Liquids are incompressible, so when liquid reaches a cylinder it creates hydraulic forces the compressor was not designed to absorb. This can break valves, bend rods, and wash oil from cylinder walls.

Question 35Industrial Refrigeration I

The main purpose of blowdown from an evaporative condenser sump is to:

  1. Lower the water level during cold weather
  2. Control dissolved solids in the circulating water Correct answer.
  3. Increase the approach temperature of the condenser
  4. Remove oil from the refrigerant circuit

Explanation

As water evaporates, dissolved minerals stay behind and concentrate in the sump. Blowdown removes a portion of that water and replaces it with fresh water to hold the concentration within acceptable limits and limit scale.

Question 36Industrial Refrigeration I

A hydrostatic relief valve installed between two block valves in a liquid line protects the trapped section from:

  1. Air entering during maintenance
  2. Vacuum caused by a pump-down cycle
  3. Refrigerant loss during a defrost cycle
  4. Overpressure from expanding trapped liquid Correct answer.

Explanation

Liquid trapped between closed valves warms toward ambient and expands, which can generate very high hydraulic pressure. The hydrostatic relief valve opens to limit that pressure and protect the piping and components.

Question 37Industrial Refrigeration I

A thermostatic expansion valve that continually hunts is most often the result of:

  1. A condenser that is too clean
  2. Insufficient refrigerant charge in the receiver
  3. A valve oversized for the evaporator load Correct answer.
  4. A valve that is too small for the evaporator

Explanation

An oversized valve makes large flow changes for small changes in superheat, so it repeatedly overfeeds and underfeeds the coil. Sizing the valve to the actual evaporator capacity stabilizes superheat control.

Question 38Industrial Refrigeration I

A compressor has a suction pressure of 15 psig and a discharge pressure of 165 psig. Using an atmospheric pressure of 15 psi, what is the compression ratio?

  1. 6.0 Correct answer.
  2. 11.0
  3. 12.0
  4. 5.5

Explanation

Compression ratio is calculated with absolute pressures: gauge pressure plus atmospheric pressure. The absolute suction is 30 psia and the absolute discharge is 180 psia, so the ratio is 180 divided by 30, or 6.0.

Question 39Industrial Refrigeration I

A very large temperature difference between the room air and the evaporator refrigerant tends to:

  1. Maintain a higher suction pressure and reduce power
  2. Reduce dehumidification and keep the room drier
  3. Have no effect on coil performance or humidity
  4. Increase dehumidification and coil frost Correct answer.

Explanation

A large temperature difference means the coil surface runs much colder than the room air. That increases moisture removal and frost formation while lowering suction pressure and compressor capacity.

Question 40Industrial Refrigeration I

An oil pressure safety switch on a reciprocating compressor trips based on:

  1. The difference between discharge and suction pressure
  2. Oil pump discharge pressure alone
  3. Crankcase pressure alone
  4. Oil pump pressure minus crankcase pressure Correct answer.

Explanation

The switch monitors net oil pressure, which is the oil pump discharge pressure minus crankcase pressure. This net value reflects the pressure actually available to force oil through the bearings.

Question 41Industrial Refrigeration II (Systems)

On a typical ammonia refrigeration system, where is the oil separator installed?

  1. At the top of the low-pressure receiver
  2. In the discharge line ahead of the condenser Correct answer.
  3. In the liquid line just ahead of the expansion valve
  4. On the suction line just ahead of the compressor suction valve

Explanation

Oil leaves the compressor entrained in hot discharge gas, so the separator is placed in the discharge line ahead of the condenser. Removing oil there prevents it from coating condenser and evaporator surfaces and lets it be returned to the crankcase.

Question 42Industrial Refrigeration II (Systems)

What is the primary function of a low-pressure receiver (surge drum) in a liquid overfeed system?

  1. To condense hot discharge gas before the condenser
  2. To raise the pressure of the flash gas returning to the compressor
  3. To store oil that leaves the compressor
  4. To separate liquid from suction gas and feed the pumps Correct answer.

Explanation

The low-pressure receiver operates at suction pressure and acts as both a liquid/vapor separator and a liquid reservoir. It supplies dry gas to the compressor and a steady supply of liquid for the refrigerant pumps.

Question 43Industrial Refrigeration II (Systems)

What is the main benefit of subcooling liquid refrigerant before it reaches the expansion valve?

  1. It lowers the condensing pressure
  2. It increases the refrigerating effect per pound Correct answer.
  3. It reduces the compressor discharge temperature noticeably
  4. It raises the evaporating pressure

Explanation

Subcooling removes sensible heat from the liquid, so each pound of refrigerant absorbs more heat in the evaporator before it is fully vaporized. The result is a larger net refrigerating effect and less flash gas at the expansion valve.

Question 44Industrial Refrigeration II (Systems)

What is the purpose of a noncondensable purge unit on an ammonia system?

  1. To remove ammonia vapor from the liquid line
  2. To remove air and other noncondensables from the high side Correct answer.
  3. To remove oil from the evaporator
  4. To remove water vapor from the liquid refrigerant before the expansion valve

Explanation

Air and other noncondensable gases accumulate in the condenser and raise condensing pressure, wasting compressor energy. The purge unit collects these gases at the high side and vents them while recovering the ammonia mixed with them.

Question 45Industrial Refrigeration II (Systems)

A liquid overfeed system operating at a 3:1 recirculation ratio pumps how much liquid relative to the amount evaporated?

  1. Three pounds of liquid for each pound of compressor discharge
  2. Three pounds of liquid for every pound evaporated Correct answer.
  3. One pound of liquid for every three pounds evaporated
  4. One pound of liquid for each pound evaporated

Explanation

The recirculation ratio compares the mass of liquid pumped to the evaporator with the mass that actually boils off there. A 3:1 ratio means three times as much liquid is circulated as is evaporated, with the excess returning to the receiver.

Question 46Industrial Refrigeration II (Systems)

What effect does heavy frost buildup have on an evaporator's performance?

  1. It raises the coil's effective surface area
  2. It insulates the coil and reduces heat transfer Correct answer.
  3. It increases the air-side heat transfer coefficient
  4. It increases the refrigerant flow through the coil

Explanation

Frost is a layer of ice that acts as an insulator between the refrigerant and the air, and it also blocks airflow between the fins. Heat transfer and capacity fall, so the coil must run colder to do the same job.

Question 47Industrial Refrigeration II (Systems)

Why is blowdown necessary on an evaporative condenser or cooling tower?

  1. To control dissolved solids buildup in the circulating water Correct answer.
  2. To add makeup water to the sump
  3. To raise the water temperature for better evaporation
  4. To increase the concentration of dissolved solids in the sump water

Explanation

As water evaporates, the dissolved minerals stay behind and concentrate in the sump, eventually causing scale and corrosion. Blowdown deliberately wastes a portion of the circulating water to hold the solids concentration at an acceptable level.

Question 48Industrial Refrigeration II (Systems)

Which defrost method uses warm compressor discharge gas to melt frost from an evaporator?

  1. Electric resistance defrost
  2. Hot gas defrost Correct answer.
  3. Water spray defrost
  4. Off-cycle air defrost

Explanation

Hot gas defrost routes warm discharge vapor through the coil so the frost melts from the inside out while the coil is valved off from the low side. The condensed refrigerant is then returned to the receiver or another part of the system.

Question 49Industrial Refrigeration II (Systems)

In a two-stage ammonia system, what is the main purpose of the intercooler?

  1. To cool booster discharge gas before the high-stage compressor Correct answer.
  2. To subcool liquid from the condenser to the evaporating temperature
  3. To condense discharge gas from the high-stage compressor
  4. To remove oil from the booster discharge gas

Explanation

Booster discharge gas is hot and must be cooled to near the intermediate saturation temperature before entering the high-stage compressor. The intercooler accomplishes this, which lowers high-stage discharge temperature and improves overall efficiency.

Question 50Industrial Refrigeration II (Systems)

Why is a cascade system used instead of a single-stage system?

  1. To reach very low temperatures beyond a single refrigerant's range Correct answer.
  2. To allow a single refrigerant to serve all of the temperature levels in the plant
  3. To reduce the number of compressors required
  4. To eliminate the need for a condenser

Explanation

A cascade pairs two separate refrigeration circuits in series, each using a refrigerant suited to its temperature band. This allows very low evaporating temperatures to be reached without the extreme compression ratios and discharge temperatures a single-stage system would face.