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SOLAS Refrigeration study materials
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SOLAS Refrigeration practice questions

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Question 1Refrigeration and Air Conditioning (craft apprenticeship curriculum)

On a SOLAS refrigeration system, what is the primary function of the compressor?

  1. To reduce the pressure of liquid refrigerant before it enters the evaporator
  2. To raise the pressure and temperature of the refrigerant vapour so it can reject heat Correct answer.
  3. To remove moisture and contaminants from the refrigerant circuit
  4. To absorb heat from the refrigerated space and cool the air directly

Explanation

The compressor draws low-pressure vapour from the evaporator and compresses it to a higher pressure, which also raises its saturation temperature so heat can be rejected in the condenser. The actual cooling of the space happens in the evaporator, not the compressor.

Question 2Refrigeration and Air Conditioning (craft apprenticeship curriculum)

In the vapour-compression cycle used on board ship, heat is rejected from the refrigerant in which component?

  1. Evaporator
  2. Condenser Correct answer.
  3. Expansion valve
  4. Compressor

Explanation

The condenser removes heat from the high-pressure refrigerant vapour, causing it to condense to liquid. This rejected heat is carried away by seawater or air. The evaporator does the opposite, absorbing heat from the space being cooled.

Question 3Refrigeration and Air Conditioning (craft apprenticeship curriculum)

Which refrigerant is commonly used in modern SOLAS-compliant ship refrigeration because it has zero ozone-depletion potential?

  1. R-22
  2. R-12
  3. R-134a Correct answer.
  4. R-717 (ammonia)

Explanation

R-134a is a hydrofluorocarbon with zero ozone-depletion potential and is widely used in marine refrigeration as a replacement for CFCs. R-12 and R-22 are ozone-depleting substances restricted under the Montreal Protocol. R-717 has zero ODP but is toxic and used mainly in large industrial plants.

Question 4Refrigeration and Air Conditioning (craft apprenticeship curriculum)

What is the purpose of the expansion valve in a refrigeration circuit?

  1. To store liquid refrigerant and separate oil from the vapour
  2. To compress the refrigerant vapour before it enters the condenser
  3. To throttle refrigerant from condensing pressure to evaporating pressure and control flow to the evaporator Correct answer.
  4. To filter out moisture and acid from the refrigerant

Explanation

The expansion valve creates the pressure drop between the high side and low side of the system and meters refrigerant into the evaporator. This drop lowers the refrigerant's saturation temperature so it can absorb heat. It does not compress, store, or filter refrigerant.

Question 5Refrigeration and Air Conditioning (craft apprenticeship curriculum)

A ship's provision room refrigeration plant shows a low suction pressure and the evaporator is frosting unevenly. Which reading should the technician check first to confirm a refrigerant undercharge?

  1. The compressor oil level
  2. The evaporator fan speed
  3. The seawater outlet temperature
  4. The condenser subcooling and sight-glass condition Correct answer.

Explanation

Low subcooling and bubbles in the sight glass are classic indicators of an undercharged system. Checking subcooling confirms whether the condenser is properly filled with liquid refrigerant. Oil level and fan speed do not directly indicate charge level.

Question 6Refrigeration and Air Conditioning (craft apprenticeship curriculum)

Why must a refrigeration system be evacuated before charging with refrigerant?

  1. To remove air and moisture that would cause high condensing pressure and acid formation Correct answer.
  2. To increase the oil viscosity in the crankcase
  3. To test the electrical insulation of the compressor motor
  4. To cool the compressor before start-up

Explanation

Evacuation removes non-condensable gases and water vapour from the circuit. Air raises condensing pressure and reduces efficiency, while moisture can form acids and cause ice blockage at the expansion valve. Cooling, oil viscosity, and insulation testing are unrelated to evacuation.

Question 7Refrigeration and Air Conditioning (craft apprenticeship curriculum)

On a marine refrigeration plant, what does a high condenser approach temperature most likely indicate?

  1. An overcharge of refrigerant
  2. A faulty evaporator fan
  3. Fouled or scaled condenser tubes reducing heat transfer Correct answer.
  4. A blocked suction filter

Explanation

A rising approach temperature (condensing temperature minus seawater temperature) usually means the condenser is not rejecting heat efficiently, often due to fouling or scaling on the seawater side. Overcharge and evaporator faults would show different symptoms. Cleaning the tubes restores the approach value.

Question 8Refrigeration and Air Conditioning (craft apprenticeship curriculum)

What is the main safety hazard of ammonia (R-717) refrigerant in a ship's refrigeration plant?

  1. It depletes the ozone layer rapidly
  2. It is toxic and can cause severe injury if it leaks into occupied spaces Correct answer.
  3. It is completely odourless and undetectable
  4. It is a greenhouse gas with a very high global-warming potential

Explanation

Ammonia is toxic and corrosive to the eyes and respiratory tract, so leak detection and ventilation are critical. It has zero ozone-depletion potential and a low global-warming potential, and it has a strong characteristic odour. The primary hazard is toxicity to personnel.

Question 9Refrigeration and Air Conditioning (craft apprenticeship curriculum)

Which instrument is used to measure the superheat at the evaporator outlet of a ship's refrigeration system?

  1. A hydrometer to measure refrigerant density
  2. Two pressure gauges and two thermometers to compare suction pressure and outlet temperature Correct answer.
  3. A tachometer to measure fan speed
  4. A megger to measure motor insulation

Explanation

Superheat is the difference between the actual suction temperature and the saturation temperature corresponding to suction pressure. It is found by reading suction pressure on a gauge and converting it to saturation temperature, then comparing with a thermometer at the evaporator outlet. The other instruments measure unrelated quantities.

Question 10Refrigeration and Air Conditioning (craft apprenticeship curriculum)

What is the purpose of the oil separator in a marine refrigeration compressor discharge line?

  1. To cool the discharge gas before it reaches the condenser
  2. To filter refrigerant moisture from the high side
  3. To remove entrained lubricating oil from the discharge gas and return it to the crankcase Correct answer.
  4. To reduce discharge pulsation and noise

Explanation

The oil separator captures oil carried over with the hot discharge gas and returns it to the compressor crankcase. This prevents oil from accumulating in the condenser and evaporator, where it would reduce heat transfer. It does not cool the gas, dry the refrigerant, or act as a pulsation damper.

Question 11Refrigeration and Air Conditioning (craft apprenticeship curriculum)

A provision store refrigeration unit is short-cycling (starting and stopping frequently). Which cause is most consistent with this symptom?

  1. A correctly sized expansion valve operating at design conditions
  2. An evaporator fan running at full speed
  3. A low refrigerant charge causing the low-pressure switch to trip Correct answer.
  4. A condenser that is too clean

Explanation

Short-cycling often results from a low-pressure cut-out tripping because the suction pressure falls below the setpoint, which can be caused by a low charge or a restriction. A clean condenser and correctly operating fan and valve would give stable running. The cycling indicates a control or charge problem.

Question 12Refrigeration and Air Conditioning (craft apprenticeship curriculum)

Which statement correctly describes the state of the refrigerant as it leaves the evaporator in a properly operating system?

  1. Supercritical gas above the critical point
  2. Slightly superheated vapour with no liquid droplets Correct answer.
  3. Subcooled liquid at high pressure
  4. A two-phase mixture of mostly liquid

Explanation

In a correctly charged system the refrigerant leaves the evaporator as vapour with a small amount of superheat, ensuring no liquid reaches the compressor. Subcooled liquid is found at the condenser outlet, and a mostly liquid mixture would indicate flooding. Supercritical operation is not normal for these plants.

Question 13Refrigeration and Air Conditioning (craft apprenticeship curriculum)

Why is a receiver fitted between the condenser and the expansion valve on a ship's refrigeration plant?

  1. To remove oil from the refrigerant
  2. To reduce the discharge temperature
  3. To store liquid refrigerant and ensure a solid liquid supply to the expansion valve Correct answer.
  4. To increase the suction pressure

Explanation

The receiver holds liquid refrigerant so that the expansion valve always receives bubble-free liquid, regardless of load changes. It also provides storage for pump-down and maintenance. It does not change suction pressure, separate oil, or cool the discharge.

Question 14Refrigeration and Air Conditioning (craft apprenticeship curriculum)

What does a pressure-enthalpy diagram allow a refrigeration technician to determine for a marine plant?

  1. The cooling capacity, compressor work, and coefficient of performance Correct answer.
  2. The oil change interval
  3. The electrical resistance of the compressor winding
  4. The seawater flow rate through the condenser

Explanation

By plotting the cycle on a pressure-enthalpy chart, the technician reads enthalpy differences to calculate refrigerating effect, compressor work, and COP. It does not measure electrical resistance, seawater flow, or maintenance intervals. These are found by other instruments and schedules.

Question 15Refrigeration and Air Conditioning (craft apprenticeship curriculum)

During a routine check, a technician finds frost forming on the suction line right up to the compressor. What does this indicate?

  1. The system is correctly charged and operating efficiently
  2. The expansion valve is stuck closed
  3. The condenser is over-cooled
  4. Liquid refrigerant is reaching the compressor, risking slugging damage Correct answer.

Explanation

Frost on the suction line up to the compressor suggests liquid refrigerant is returning instead of superheated vapour. This can cause slugging, oil dilution, and compressor damage. A properly operating system has superheat at the evaporator outlet and frost confined to the evaporator.

Question 16Refrigeration and Air Conditioning (craft apprenticeship curriculum)

What is the function of the crankcase heater on a marine refrigeration compressor?

  1. To keep oil warm so refrigerant does not condense and dilute it during shutdown Correct answer.
  2. To raise the evaporating temperature
  3. To heat the discharge gas before it enters the condenser
  4. To warm the seawater supply to the condenser

Explanation

During shutdown, refrigerant can migrate and condense in the crankcase, diluting the oil and causing poor lubrication on start-up. The crankcase heater keeps the oil above the refrigerant's condensing temperature to prevent this. It does not heat discharge gas, raise evaporating temperature, or warm seawater.

Question 17Refrigeration and Air Conditioning (craft apprenticeship curriculum)

A ship's air-conditioning plant uses chilled water. What is the role of the chilled-water pump in this system?

  1. To control the expansion valve opening
  2. To compress the refrigerant vapour
  3. To circulate chilled water from the evaporator to the air-handling units Correct answer.
  4. To reject heat to the seawater

Explanation

In a chilled-water air-conditioning system, the pump moves the cooled water from the evaporator to the air-handling units, where it absorbs heat from the air. The compressor handles refrigerant compression, the condenser rejects heat, and the expansion valve is controlled by its own sensing bulb.

Question 18Refrigeration and Air Conditioning (craft apprenticeship curriculum)

Which practice is required when handling refrigerant cylinders on board under SOLAS-related safety procedures?

  1. Store cylinders next to the boiler for warmth
  2. Lay cylinders horizontally to save space
  3. Fill cylinders completely to liquid level before storage
  4. Store cylinders upright, secured, away from heat, and in a ventilated space Correct answer.

Explanation

Refrigerant cylinders must be kept upright and secured against rolling, away from heat sources, and in a well-ventilated area to prevent pressure build-up and asphyxiation risk. Laying them down, heating them, or overfilling them creates serious hazards. These precautions protect both personnel and the vessel.

Question 19Refrigeration and Air Conditioning (craft apprenticeship curriculum)

What does a high discharge pressure combined with normal suction pressure most likely indicate in a seawater-cooled condenser?

  1. A blocked suction line
  2. A refrigerant undercharge
  3. A failed evaporator fan
  4. Insufficient seawater flow or a fouled condenser Correct answer.

Explanation

High discharge pressure with normal suction points to the high side, commonly poor condenser heat rejection from low seawater flow or fouling. Undercharge and suction-side faults would lower suction pressure or affect the low side. The condenser and its water circuit should be inspected first.

Question 20Refrigeration and Air Conditioning (craft apprenticeship curriculum)

A technician needs to calculate the coefficient of performance of a marine refrigeration cycle. Which ratio is correct?

  1. Condenser heat rejected divided by evaporator heat absorbed
  2. Compressor work input divided by refrigerating effect
  3. Refrigerating effect divided by compressor work input Correct answer.
  4. Suction pressure divided by discharge pressure

Explanation

COP is defined as the useful cooling (refrigerating effect) divided by the work supplied by the compressor. A higher COP means more cooling per unit of energy input. The inverse ratio and pressure ratios do not represent COP.

Question 21Refrigeration and Air Conditioning (craft apprenticeship curriculum)

Why is a thermostatic expansion valve's sensing bulb clamped to the evaporator outlet rather than the inlet?

  1. To detect the condenser pressure
  2. To sense the compressor oil temperature
  3. To sense the superheat of the vapour leaving the evaporator and modulate refrigerant flow Correct answer.
  4. To measure the liquid temperature entering the evaporator

Explanation

The bulb senses the temperature at the evaporator outlet, which together with suction pressure indicates superheat. The valve then adjusts flow to maintain the set superheat, preventing both flooding and starvation. Mounting at the inlet would not reflect the actual superheat.

Question 22Refrigeration and Air Conditioning (craft apprenticeship curriculum)

A marine refrigeration system is being commissioned and the technician records a very high superheat at the evaporator outlet with low suction pressure. What is the most likely cause?

  1. The condenser is fouled
  2. The system is overcharged with refrigerant
  3. The compressor is unloaded
  4. The expansion valve is underfeeding due to a restriction or lost bulb charge Correct answer.

Explanation

High superheat with low suction pressure means the evaporator is starved of refrigerant, often because the expansion valve is restricted or its bulb charge has been lost. Overcharge and condenser fouling affect the high side, and an unloaded compressor would show different symptoms. The valve should be inspected.

Question 23Refrigeration and Air Conditioning (craft apprenticeship curriculum)

What is the main reason for using a water-cooled condenser instead of an air-cooled condenser on a large ocean-going ship?

  1. Air is unavailable in the engine room
  2. Water-cooled condensers require no maintenance
  3. Seawater provides a reliable, compact heat sink with stable temperature for high heat rejection Correct answer.
  4. Air-cooled condensers cannot use R-134a

Explanation

Seawater is abundant, has a stable temperature, and allows a compact condenser to reject large heat loads efficiently. Air-cooled units would need much larger surface areas and are affected by ambient conditions. Maintenance is still required, and air-cooled units can use R-134a.

Question 24Refrigeration and Air Conditioning (craft apprenticeship curriculum)

Which safety device protects a refrigeration compressor from excessively high discharge pressure?

  1. A thermal expansion valve
  2. A low-pressure cut-out switch
  3. A suction line accumulator
  4. A high-pressure cut-out switch Correct answer.

Explanation

The high-pressure cut-out stops the compressor when discharge pressure exceeds a safe limit, preventing component damage or rupture. A low-pressure switch protects against low suction, while the expansion valve and accumulator serve control and liquid-protection functions.

Question 25Refrigeration and Air Conditioning (craft apprenticeship curriculum)

A technician observes that the compressor runs continuously but the provision room does not reach the set temperature. Which combination best explains this?

  1. A correctly operating system at design load
  2. A crankcase heater left on during running
  3. Reduced cooling capacity from a worn compressor or a restricted expansion valve Correct answer.
  4. A high-pressure cut-out that has tripped

Explanation

Continuous running without achieving temperature indicates the system's cooling capacity is below the load, often from compressor wear or a restricted expansion valve. A tripped high-pressure cut-out would stop the compressor, and a crankcase heater left on would not cause continuous running. Normal design operation would meet the setpoint.

Question 26Refrigeration and Air Conditioning (craft apprenticeship curriculum)

In a vapour-compression refrigeration cycle, what is the primary function of the compressor?

  1. To remove moisture and non-condensable gases from the refrigerant
  2. To reduce refrigerant pressure before it enters the evaporator
  3. To cool the refrigerant below its saturation temperature
  4. To raise the refrigerant pressure so it can reject heat at the condenser Correct answer.

Explanation

The compressor takes low-pressure vapour from the evaporator and raises its pressure and temperature so that heat can be rejected to the ambient or seawater in the condenser. The pressure reduction job belongs to the expansion device, not the compressor.

Question 27Refrigeration and Air Conditioning (craft apprenticeship curriculum)

What is the state of the refrigerant entering the expansion valve of a correctly operating marine refrigeration plant?

  1. High-pressure superheated vapour
  2. Low-pressure superheated vapour
  3. Low-pressure two-phase mixture
  4. High-pressure liquid, often slightly subcooled Correct answer.

Explanation

The expansion valve receives liquid refrigerant that has been condensed and usually slightly subcooled, so that only liquid passes through the small port. If vapour reaches the valve, its capacity drops sharply and control becomes unstable.

Question 28Refrigeration and Air Conditioning (craft apprenticeship curriculum)

Which refrigerant is now widely used in new ship refrigeration plants because it has zero ozone-depletion potential?

  1. R-22
  2. R-134a Correct answer.
  3. R-404A
  4. R-717 (ammonia)

Explanation

R-134a is an HFC with zero ozone-depletion potential and is common in marine plants replacing CFC and HCFC refrigerants. R-22 is an HCFC with a measurable ODP and is being phased out under the Montreal Protocol.

Question 29Refrigeration and Air Conditioning (craft apprenticeship curriculum)

What does the term 'superheat' mean at the outlet of an evaporator?

  1. The amount of liquid refrigerant carried over into the suction line
  2. The extra pressure the compressor adds above the condenser pressure
  3. The temperature difference between condenser water in and out
  4. The temperature rise of the vapour above its saturation temperature at that pressure Correct answer.

Explanation

Superheat is the number of degrees the vapour is above the saturation temperature for its pressure. It confirms that all liquid has boiled off before the vapour reaches the compressor.

Question 30Refrigeration and Air Conditioning (craft apprenticeship curriculum)

Why is a thermostatic expansion valve fitted with an external equaliser line on many marine evaporators?

  1. To bypass the valve during the defrost cycle
  2. To allow the valve to be adjusted without opening the plant
  3. To connect the sensing bulb directly to the suction service valve
  4. To compensate for the pressure drop across the evaporator when sizing the valve opening Correct answer.

Explanation

On evaporators with a significant pressure drop, the pressure at the valve outlet differs from the pressure at the bulb location. The external equaliser feeds the true suction pressure to the underside of the diaphragm so the valve controls the correct superheat.

Question 31Refrigeration and Air Conditioning (craft apprenticeship curriculum)

A technician measures a suction pressure of 2.0 bar gauge and a suction temperature of -5 degrees C. If the saturation temperature at 2.0 bar gauge is -15 degrees C, what is the superheat?

  1. 20 K
  2. 5 K
  3. 15 K
  4. 10 K Correct answer.

Explanation

Superheat is the measured suction temperature minus the saturation temperature at the same pressure. Here -5 degrees C minus -15 degrees C gives 10 K.

Question 32Refrigeration and Air Conditioning (craft apprenticeship curriculum)

What is the purpose of the liquid line sight glass with a moisture indicator on a marine refrigeration plant?

  1. To show whether the refrigerant is fully liquid and free of harmful moisture Correct answer.
  2. To display the evaporator superheat directly
  3. To measure the condenser water flow rate
  4. To indicate the compressor oil level in the crankcase

Explanation

Bubbles in the sight glass indicate a shortage of liquid or flashing in the liquid line, while the colour-change element warns of moisture. Both are early indicators of charging or dehydration faults.

Question 33Refrigeration and Air Conditioning (craft apprenticeship curriculum)

Which effect does a restricted filter-drier in the liquid line have on the operation of a marine refrigeration plant?

  1. It raises the suction pressure and increases evaporator capacity
  2. It has no effect as long as the compressor runs
  3. It increases the compressor discharge pressure only
  4. It causes a pressure drop and flashing in the liquid line, reducing evaporator capacity Correct answer.

Explanation

A blocked drier drops the pressure of the liquid before the expansion valve, so some refrigerant flashes to vapour. The valve then passes less liquid and the evaporator starves, reducing capacity.

Question 34Refrigeration and Air Conditioning (craft apprenticeship curriculum)

A marine refrigeration compressor is fitted with a high-pressure cut-out. What is its correct function?

  1. To start the standby compressor automatically on high pressure
  2. To regulate the seawater flow through the condenser
  3. To open the expansion valve during high load
  4. To stop the compressor when discharge pressure exceeds a safe set point Correct answer.

Explanation

The high-pressure cut-out is a safety switch that trips the compressor contactor when discharge pressure rises above the set point, protecting the compressor and piping. It does not control condenser water or the expansion valve.

Question 35Refrigeration and Air Conditioning (craft apprenticeship curriculum)

What is the main reason for fitting an oil trap or oil return arrangement in the suction line of a marine refrigeration system?

  1. To reduce suction line noise
  2. To increase the suction pressure
  3. To return oil that has migrated with the refrigerant back to the compressor crankcase Correct answer.
  4. To remove water from the refrigerant vapour

Explanation

Oil leaves the compressor with the discharge gas and travels around the circuit; the trap and proper line sizing ensure it returns to the crankcase instead of logging in the evaporator. Oil logging reduces heat transfer and can starve the compressor of lubricant.

Question 36Refrigeration and Air Conditioning (craft apprenticeship curriculum)

In a marine refrigeration plant, what does a condenser that is fouled with scale on the seawater side cause?

  1. Reduced compressor current draw
  2. Lower discharge pressure and increased capacity
  3. Higher discharge pressure and reduced plant efficiency Correct answer.
  4. Lower suction pressure only

Explanation

Scale insulates the tube surface, so heat rejection falls and the condensing temperature and discharge pressure rise. The compressor then works harder and efficiency drops.

Question 37Refrigeration and Air Conditioning (craft apprenticeship curriculum)

Which statement best describes the function of the evaporator in a ship's provision refrigeration system?

  1. It raises the refrigerant pressure to the condensing level
  2. It rejects heat to the seawater and condenses the refrigerant
  3. It meters liquid refrigerant into the circuit
  4. It absorbs heat from the refrigerated space and boils the refrigerant Correct answer.

Explanation

The evaporator is the heat exchanger where the low-pressure refrigerant boils and absorbs heat from the space being cooled. Condensation of refrigerant occurs in the condenser, not the evaporator.

Question 38Refrigeration and Air Conditioning (craft apprenticeship curriculum)

What is the purpose of a defrost cycle on a provision-room evaporator operating below 0 degrees C?

  1. To melt frost that insulates the coil and blocks airflow Correct answer.
  2. To flush oil from the evaporator back to the compressor
  3. To raise the refrigerated space temperature for cargo reasons
  4. To increase the refrigerant charge in the system

Explanation

Frost on the coil acts as an insulator and restricts air passage, so periodic defrosting restores heat transfer. It is a maintenance function, not a means of warming the cargo space.

Question 39Refrigeration and Air Conditioning (craft apprenticeship curriculum)

A technician finds the suction pressure is lower than normal and the evaporator is frosted only near the inlet. Which fault is most likely?

  1. Overcharge of refrigerant
  2. A failed crankcase heater
  3. Excessive seawater flow through the condenser
  4. Undercharge of refrigerant or a partially blocked expansion valve Correct answer.

Explanation

A starved evaporator shows low suction pressure and frosting confined to the first part of the coil, consistent with a shortage of refrigerant or a restricted valve. Overcharging causes high suction and discharge pressures, not starvation.

Question 40Refrigeration and Air Conditioning (craft apprenticeship curriculum)

What is the primary purpose of a pressure-enthalpy chart in marine refrigeration work?

  1. To set the cut-in and cut-out points of the thermostat
  2. To determine the compressor oil viscosity
  3. To calculate cycle performance such as refrigerating effect and compressor work Correct answer.
  4. To size the seawater piping for the condenser

Explanation

The P-h chart plots the cycle so the refrigerating effect, compressor work and coefficient of performance can be calculated from enthalpy differences. It is not a piping or thermostat-setting tool.

Question 41Refrigeration and Air Conditioning (craft apprenticeship curriculum)

On a marine refrigeration system, what does a low suction pressure combined with a normal discharge pressure most likely indicate?

  1. A restricted liquid line or a partly closed suction valve Correct answer.
  2. A failed condenser water pump
  3. An overcharged system
  4. A fouled seawater condenser

Explanation

When suction pressure falls but discharge pressure stays normal, the problem is on the low side, such as a restriction or a partially closed valve. Condenser-side faults would raise discharge pressure instead.

Question 42Refrigeration and Air Conditioning (craft apprenticeship curriculum)

What is the purpose of a liquid receiver in a marine refrigeration plant using an expansion valve?

  1. To superheat the vapour before it reaches the compressor
  2. To cool the compressor crankcase oil
  3. To store liquid refrigerant and accommodate changes in charge within the circuit Correct answer.
  4. To separate oil from the discharge gas

Explanation

The receiver holds liquid refrigerant so the expansion valve always has a liquid seal and so the system can accommodate varying charge requirements. It does not separate oil or superheat vapour.

Question 43Refrigeration and Air Conditioning (craft apprenticeship curriculum)

Which refrigerant property makes it suitable for a very low-temperature marine freezer plant?

  1. A high solubility in compressor oil
  2. A strong odour for leak detection
  3. A high specific heat in the liquid state
  4. A low boiling point at the evaporating pressure required Correct answer.

Explanation

A refrigerant must boil at the low temperature required by the freezer at a pressure the compressor can handle. A low boiling point at the design evaporating pressure is the key selection criterion.

Question 44Refrigeration and Air Conditioning (craft apprenticeship curriculum)

A marine refrigeration plant uses R-404A. Which statement about its handling is correct?

  1. It must be charged as a gas to prevent oil foaming
  2. It is an azeotrope and can be charged as vapour without change in composition
  3. It is a zeotropic blend and must be charged as a liquid to avoid fractionation Correct answer.
  4. It is a single-component refrigerant with no glide

Explanation

R-404A is a zeotropic blend with a temperature glide, so if it is charged as vapour the more volatile components leave first and the cylinder composition changes. It must be charged as a liquid.

Question 45Refrigeration and Air Conditioning (craft apprenticeship curriculum)

What is the function of a compressor unloader or capacity control device on a marine refrigeration plant?

  1. To drain oil from the crankcase
  2. To unload refrigerant from the receiver during maintenance
  3. To bypass the condenser during low load
  4. To match compressor capacity to the evaporator load and prevent short cycling Correct answer.

Explanation

Capacity control reduces the compressor's output when the load falls, allowing it to run continuously at a matched capacity instead of cycling on and off. This improves temperature stability and reduces wear.

Question 46Refrigeration and Air Conditioning (craft apprenticeship curriculum)

Which condition would cause a refrigeration compressor to trip repeatedly on its motor overload?

  1. A slightly low suction pressure
  2. A correctly set thermostatic expansion valve
  3. A high discharge pressure caused by a fouled condenser Correct answer.
  4. A clean liquid line sight glass

Explanation

High discharge pressure raises the compressor's power demand and current draw, which can trip the overload. Correct expansion valve operation and a clean sight glass are normal conditions.

Question 47Refrigeration and Air Conditioning (craft apprenticeship curriculum)

Why is a crankcase pressure regulator sometimes fitted to a marine refrigeration compressor?

  1. To raise the discharge pressure during hot weather
  2. To open the expansion valve on start-up
  3. To limit suction pressure during pull-down so the motor is not overloaded Correct answer.
  4. To control the condenser water temperature

Explanation

On start-up or after defrost, suction pressure can be high enough to overload the compressor motor. A crankcase pressure regulator throttles the suction gas until the evaporator pressure falls.

Question 48Refrigeration and Air Conditioning (craft apprenticeship curriculum)

Which statement correctly describes the relationship between condenser approach temperature and condenser cleanliness?

  1. A falling approach temperature always indicates fouling
  2. Approach temperature is independent of tube condition
  3. A rising approach temperature indicates improved heat transfer
  4. A rising approach temperature indicates fouling or reduced water flow Correct answer.

Explanation

Approach temperature is the difference between condensing temperature and leaving water temperature. As tubes foul or water flow falls, the condenser cannot reject heat as effectively and the approach increases.

Question 49Refrigeration and Air Conditioning (craft apprenticeship curriculum)

In a ship's air-conditioning system, what is the purpose of the reheater coil downstream of the cooling coil?

  1. To remove moisture from the supply air
  2. To cool the air below its dew point
  3. To raise the supply air temperature to the desired room condition after dehumidification Correct answer.
  4. To increase the refrigerant pressure in the chiller

Explanation

Cooling the air to remove moisture also lowers its temperature, so a reheater brings it back to a comfortable supply condition. It does not perform the dehumidification itself.

Question 50Refrigeration and Air Conditioning (craft apprenticeship curriculum)

What is the correct action when a leak of R-134a is detected in an enclosed machinery space on board?

  1. Ignore it because R-134a is non-toxic
  2. Evacuate and ventilate the space, then locate and repair the leak using PPE Correct answer.
  3. Add refrigerant to compensate without repairing the leak
  4. Seal the space and continue running the plant

Explanation

Although R-134a has low toxicity, it displaces oxygen and decomposes into harmful products near hot surfaces, so the space must be ventilated and the leak repaired with proper PPE. Topping up without repair is both unsafe and illegal under refrigerant regulations.