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Cert III Air Conditioning & Refrigeration study materials
Cert III Air Conditioning & Refrigeration study resources

Cert III Air Conditioning & Refrigeration practice questions

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Question 1Work Health and Safety and Environmental Compliance

Under Australian WHS law, what is the primary duty of a person conducting a business or undertaking (PCBU) in relation to refrigeration work?

  1. To provide personal protective equipment free of charge to all visitors
  2. To ensure workers hold a current refrigerant handling licence before any work begins
  3. To report every near miss to the regulator within 24 hours
  4. To eliminate or minimise risks to health and safety so far as is reasonably practicable Correct answer.

Explanation

The model WHS Act imposes a primary duty on the PCBU to ensure health and safety so far as is reasonably practicable, which includes eliminating or minimising risks. Licensing, incident notification and PPE are separate obligations that flow from this duty rather than replacing it. The reasonably practicable test weighs the likelihood and severity of harm against the cost and difficulty of controls.

Question 2Work Health and Safety and Environmental Compliance

Which document should a technician consult first to understand the specific hazards of a new refrigerant before charging a system?

  1. The electrical wiring diagram for the condensing unit
  2. The equipment maintenance log for the previous year
  3. The manufacturer's safety data sheet for that refrigerant Correct answer.
  4. The site's emergency evacuation floor plan

Explanation

A safety data sheet provides the hazard classification, exposure controls, first aid measures and safe handling advice for a specific chemical. Technicians must review it before using an unfamiliar refrigerant so controls match the actual hazards, such as flammability or toxicity. Other site documents do not describe the chemical properties of the substance.

Question 3Work Health and Safety and Environmental Compliance

A refrigerant cylinder must be stored and transported in which orientation to keep the valve and safety devices in contact with vapour rather than liquid?

  1. Inverted so the valve is at the lowest point
  2. Lying horizontally with the valve pointing down
  3. Upright and secured against falling Correct answer.
  4. At any angle provided the cap is fitted

Explanation

Cylinders are designed so that when upright the valve and pressure relief device communicate with the vapour space. Storing or transporting them upright and secured prevents liquid refrigerant entering the valve and reduces the risk of uncontrolled discharge if a fitting fails. Liquid entering a regulator or hose can cause violent pressure spikes and cold burns.

Question 4Work Health and Safety and Environmental Compliance

Which piece of personal protective equipment is essential when there is a risk of liquid refrigerant contacting the skin during hose connection?

  1. Disposable latex examination gloves
  2. Cryogenic-rated gloves with a loose cuff Correct answer.
  3. Fingerless leather work gloves
  4. Cotton riggers gloves

Explanation

Liquid refrigerant boils at very low temperatures and can cause frostbite or cold burns on contact with skin. Cryogenic-rated gloves insulate against extreme cold, and a loose cuff allows the glove to be thrown off quickly if liquid becomes trapped inside. Ordinary work gloves offer no meaningful thermal protection.

Question 5Work Health and Safety and Environmental Compliance

What is the main purpose of performing a nitrogen pressure test before evacuating a newly installed refrigeration system?

  1. To verify that the compressor motor windings are electrically sound
  2. To calibrate the low-pressure switch set point
  3. To remove moisture from the internal surfaces of the pipework
  4. To detect leaks and prove the system's mechanical integrity under pressure Correct answer.

Explanation

A dry nitrogen pressure test raises the system above operating pressure so that joints and components can be checked for leaks and mechanical strength. Nitrogen is used because it is inert and dry, avoiding the introduction of moisture or oxygen into the system. Moisture removal is the job of evacuation, not pressure testing.

Question 6Work Health and Safety and Environmental Compliance

Why must a refrigerant recovery cylinder never be filled beyond its marked gross weight or the 80 percent liquid fill limit?

  1. To keep the cylinder light enough for one person to lift safely
  2. To ensure the recovery machine operates at its rated voltage
  3. To allow the cylinder to be used as a liquid receiver on the system
  4. To leave vapour space for liquid expansion and prevent hydraulic rupture Correct answer.

Explanation

Liquid refrigerant expands significantly as it warms, so overfilling a cylinder leaves no room for expansion and can generate hydraulic pressure that ruptures the shell. The 80 percent fill limit preserves a vapour space and keeps pressure within the cylinder's design rating. Weight limits are a pressure safety control, not a manual handling rule.

Question 7Work Health and Safety and Environmental Compliance

Which statutory instrument primarily governs the phase-out and handling of ozone-depleting substances and synthetic greenhouse gases in Australia?

  1. The Ozone Protection and Synthetic Greenhouse Gas Management Act and its regulations Correct answer.
  2. The Australian Standard for electrical installations AS/NZS 3000
  3. The National Construction Code
  4. The Heavy Vehicle National Law

Explanation

The Ozone Protection and Synthetic Greenhouse Gas Management Act and associated regulations control the import, export, manufacture and end-of-life handling of ozone-depleting substances and synthetic greenhouse gases. The Act underpins the refrigerant handling licence scheme and equipment standards. The other instruments address building, electrical and transport matters respectively.

Question 8Work Health and Safety and Environmental Compliance

A technician must decommission a small split system containing R32. Which recovery approach satisfies environmental obligations?

  1. Recover the refrigerant into a suitable recovery cylinder using recovery equipment before dismantling Correct answer.
  2. Vent the charge slowly to atmosphere to avoid a rapid pressure drop
  3. Release the charge into a sealed room and ventilate it outdoors
  4. Pump the charge into the outdoor unit and leave it sealed for disposal

Explanation

Refrigerant must be recovered using approved equipment and stored in a suitable container so it can be reclaimed or destroyed. Deliberate venting of synthetic greenhouse gases is prohibited because of their high global warming potential, and R32 is also mildly flammable. Leaving charge in equipment sent for disposal risks uncontrolled release later.

Question 9Work Health and Safety and Environmental Compliance

A flammable refrigerant such as R290 is being used in a small commercial cabinet. Which control most directly reduces the ignition risk during service?

  1. Increasing the refrigerant charge to improve cooling performance
  2. Using a standard vacuum pump without a spark-free motor
  3. Removing ignition sources and ventilating the work area before opening the circuit Correct answer.
  4. Wearing antistatic footwear throughout the service visit

Explanation

Flammable refrigerants can form an explosive mixture with air, so eliminating ignition sources and ensuring adequate ventilation before breaking into the circuit is the key control. Tools and equipment used should be rated for flammable atmospheres. Charge size and footwear do not address the accumulation of a flammable cloud.

Question 10Work Health and Safety and Environmental Compliance

During brazing on refrigerant pipework, why is it important to purge the line with dry nitrogen?

  1. To prevent oxidation inside the pipe and stop formation of scale that can block valves Correct answer.
  2. To cool the joint quickly so the filler metal sets with a finer grain
  3. To raise the internal pressure so the joint is tested while hot
  4. To act as a flux so additional flux paste is unnecessary

Explanation

Heating copper in the presence of oxygen forms copper oxide scale on the internal surface. A slow nitrogen purge displaces oxygen and keeps the bore clean, protecting valves, filters and compressors from contamination. Nitrogen also prevents the build-up of internal pressure that could blow molten filler out of the joint.

Question 11Work Health and Safety and Environmental Compliance

A worker is about to work at height on a rooftop condenser. Which hierarchy-of-control step comes before relying on a fall-arrest harness?

  1. Recording the task in the site diary
  2. Issuing the worker with a second harness as a spare
  3. Scheduling the work for cooler parts of the day
  4. Eliminating the need to work at height or providing guardrails and platforms Correct answer.

Explanation

The hierarchy of control requires higher-order measures to be applied before lower-order ones. Eliminating the need to access the roof, or providing a passive barrier such as guardrails or a platform, is preferred over a harness, which only limits the consequence of a fall. Administrative measures and PPE sit at the bottom of the hierarchy.

Question 12Work Health and Safety and Environmental Compliance

What is the correct action when a refrigerant leak is detected in a plant room containing a large ammonia charge?

  1. Increase ventilation fans to full speed and resume the task in ten minutes
  2. Evacuate the area, raise the alarm and only re-enter wearing breathing apparatus with trained personnel Correct answer.
  3. Open all doors and continue working while monitoring with a handheld detector
  4. Spray water on the leak to absorb the gas and continue the repair

Explanation

Ammonia is toxic and can cause severe respiratory injury, so a confirmed leak requires evacuation and alarm activation. Re-entry should only occur with appropriate respiratory protection by trained emergency responders. Continuing work in the area, even with detection, exposes people to an uncontrolled hazard.

Question 13Work Health and Safety and Environmental Compliance

Which practice best manages the risk of oxygen deficiency when entering a confined space such as a large chilled-water tank?

  1. Wear a dust mask and carry a mobile phone for communication
  2. Open the access hatch for five minutes and then enter alone
  3. Enter quickly to reduce the time spent inside the space
  4. Test the atmosphere for oxygen and contaminants, then issue a confined space entry permit with a standby observer Correct answer.

Explanation

Confined spaces must be assessed and tested before entry, and entry should be controlled by a permit with a standby person outside. Atmospheric testing identifies oxygen deficiency or enrichment and toxic gases before anyone is exposed. Communication and speed of entry do not substitute for testing and supervision.

Question 14Work Health and Safety and Environmental Compliance

A technician is using a recovery machine and notices the recovery cylinder becoming warm and the pressure rising quickly. What is the most appropriate response?

  1. Continue recovery and open the cylinder valve fully to relieve pressure
  2. Increase the recovery rate to finish the job before the cylinder overheats
  3. Stop recovery, check the cylinder fill level and allow the cylinder to cool before continuing Correct answer.
  4. Place the cylinder in a water bath to speed up heat transfer

Explanation

Rising temperature and pressure indicate the cylinder is approaching its fill limit or is being over-pressurised. Recovery should stop so the fill level can be verified and the cylinder allowed to cool, preventing hydraulic rupture. Never heat a recovery cylinder or force more refrigerant into it.

Question 15Work Health and Safety and Environmental Compliance

Which records must a business keep to demonstrate compliance with refrigerant handling obligations?

  1. Only the technician's trade certificate and driver licence
  2. The manufacturer's warranty registration for each unit
  3. Records of refrigerant purchases, recovery, recycling and disposal quantities and dates Correct answer.
  4. A copy of the building fire evacuation diagram

Explanation

Refrigerant handling obligations require traceability of the gas from purchase through recovery to final disposal. Records of quantities and dates allow the regulator to verify that refrigerant has not been vented. Trade certificates and building documents do not track refrigerant movement.

Question 16Work Health and Safety and Environmental Compliance

What is the purpose of a risk assessment before commencing service work on an unfamiliar refrigeration plant?

  1. To replace the need for a safe work method statement
  2. To identify hazards, assess the likelihood and consequence of harm, and select controls before work starts Correct answer.
  3. To satisfy the customer's insurance policy conditions only
  4. To allocate blame if an incident occurs during the job

Explanation

A risk assessment systematically identifies hazards and evaluates the likelihood and severity of harm so controls can be chosen and implemented. It is a proactive planning tool, not a blame-allocation or insurance exercise. It informs, but does not replace, other documents such as a safe work method statement.

Question 17Work Health and Safety and Environmental Compliance

Which gas is commonly used to pressurise a system for leak testing because it is inert and leaves no residue?

  1. Acetylene
  2. Oxygen
  3. Dry nitrogen Correct answer.
  4. Carbon dioxide

Explanation

Dry nitrogen is inert, non-flammable and dry, so it can pressurise a system without reacting with refrigerant or oil and without introducing moisture. Oxygen and acetylene are dangerous in refrigerant systems because they can support combustion or form explosive mixtures with oil. Carbon dioxide is not normally used because of its pressure-temperature characteristics and asphyxiation risk.

Question 18Work Health and Safety and Environmental Compliance

A worker reports dizziness and headache while working near an operating absorption chiller in a basement plant room. What is the most likely hazard and the correct first response?

  1. Heat stress; give the worker water and continue the task
  2. Manual handling strain; send the worker home without further action
  3. Possible refrigerant or combustion gas exposure; evacuate, ventilate and test the atmosphere before re-entry Correct answer.
  4. Noise exposure; issue earplugs and resume work

Explanation

Dizziness and headache in a plant room can indicate exposure to refrigerant vapour or combustion products, particularly where ventilation is poor. The area should be evacuated and ventilated, and the atmosphere tested before anyone returns. Symptoms should be assessed by a medical professional and the incident reported.

Question 19Work Health and Safety and Environmental Compliance

Why must a refrigerant cylinder be protected from direct sunlight and heat sources during storage?

  1. Sunlight degrades the refrigerant's lubricating properties
  2. Warm cylinders cannot be connected to recovery equipment
  3. Heat causes the cylinder's painted coating to become flammable
  4. Pressure rises with temperature and can exceed the cylinder's relief setting Correct answer.

Explanation

The pressure inside a closed cylinder follows the saturation curve of the refrigerant, so heating raises pressure towards the relief valve setting. Keeping cylinders out of direct sun and away from heat sources keeps pressure within safe limits. Refrigerant chemistry and cylinder coatings are not the reason for this control.

Question 20Work Health and Safety and Environmental Compliance

A site requires hot work for brazing near combustible insulation. Which combination of controls is most appropriate?

  1. Brazing only in the afternoon when fewer people are present
  2. A verbal warning to nearby workers and a bucket of water
  3. A fire blanket placed on the floor beneath the work area only
  4. A hot work permit, firefighting equipment on hand, a fire watch and removal or shielding of combustibles Correct answer.

Explanation

Hot work near combustibles requires a formal permit system, removal or shielding of combustible material, firefighting equipment and a fire watch during and after the work. These controls address ignition, fuel and post-work smouldering. Informal warnings or timing changes do not provide reliable protection.

Question 21Work Health and Safety and Environmental Compliance

When selecting a recovery cylinder for an HFC refrigerant, which property must the cylinder be rated for?

  1. The electrical conductivity of the cylinder material
  2. Only the liquid volume, since pressure ratings are universal
  3. The pressure and compatibility requirements of that specific refrigerant Correct answer.
  4. Any refrigerant provided the cylinder is painted grey

Explanation

Recovery cylinders must be rated for the pressure of the refrigerant being recovered and compatible with its materials. Different refrigerants have different saturation pressures, so a cylinder suitable for one may be unsuitable for another. Colour coding is a guide only and is not a substitute for checking the rating.

Question 22Work Health and Safety and Environmental Compliance

A technician finds a legacy R22 system scheduled for replacement. Which statement best reflects the environmental obligations for the existing charge?

  1. The R22 must be recovered and sent for destruction or reclamation by an authorised facility Correct answer.
  2. The R22 can be discharged into the sewer provided it is diluted
  3. The R22 may be vented because it is being phased out anyway
  4. The R22 may be burned on site to destroy the ozone-depleting substance

Explanation

R22 is an ozone-depleting substance, and its release to atmosphere is prohibited regardless of the equipment's age or phase-out status. The charge must be recovered and transferred to an authorised facility for destruction or reclamation. Dilution, venting and on-site burning are all unlawful and hazardous.

Question 23Work Health and Safety and Environmental Compliance

Why does AS/NZS 1677.2 place limits on the quantity of A2L refrigerant permitted in an occupied space?

  1. To ensure the refrigerant charge matches the compressor displacement
  2. To control the noise level produced by the indoor fan
  3. To keep any leaked concentration below the lower flammability limit given the room volume and ventilation Correct answer.
  4. To limit the cooling capacity of the equipment to the room's heat load

Explanation

A2L refrigerants are mildly flammable, so standards limit charge size relative to room volume and ventilation to keep a worst-case leak below the lower flammability limit. This prevents formation of a flammable concentration in occupied spaces. Capacity matching and noise control are separate design considerations.

Question 24Work Health and Safety and Environmental Compliance

A refrigerant leak occurs in a basement plant room with no low-level ventilation and the gas is denser than air. Which design feature most reduces the risk of accumulation?

  1. A high-level relief grille to the outdoors
  2. A low-level mechanical exhaust interlocked with a gas detection system Correct answer.
  3. An open stairwell to the floor above
  4. A portable pedestal fan kept in the plant room

Explanation

Refrigerants heavier than air pool at low level, so extraction must be taken from the lowest point. Interlocking the exhaust with gas detection ensures it operates automatically when a leak is detected. High-level openings and open stairwells do not remove gas from the floor zone.

Question 25Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

In a refrigeration system, what is the primary purpose of the compressor?

  1. To remove heat from the refrigerant liquid
  2. To raise the pressure and temperature of the refrigerant vapour Correct answer.
  3. To filter moisture and acid from the refrigerant
  4. To reduce the refrigerant pressure before the evaporator

Explanation

The compressor draws low-pressure vapour from the evaporator and compresses it, which raises both its pressure and its temperature so that heat can be rejected in the condenser. It does not itself remove heat or filter the refrigerant; those tasks belong to other components. Moving vapour from a low-pressure zone to a high-pressure zone is the essential function.

Question 26Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

Which statement correctly describes the latent heat of vaporisation?

  1. Heat absorbed or released when a substance changes state without a temperature change Correct answer.
  2. Heat lost by a hot body to a colder body by radiation only
  3. Heat released when a gas is compressed at constant pressure
  4. Heat required to raise one kilogram of a substance by one kelvin

Explanation

Latent heat is the energy exchanged during a phase change at constant temperature, such as boiling or condensing. Sensible heat, by contrast, changes the temperature of a substance without altering its state. Recognising this difference is fundamental when analysing evaporator and condenser performance.

Question 27Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

On a pressure-temperature chart for a pure refrigerant, what does the saturation curve represent?

  1. The maximum pressure the compressor can safely produce
  2. The pressure at which the refrigerant becomes a superheated vapour
  3. The point where the refrigerant has no measurable pressure
  4. The pressure at which liquid and vapour coexist at a given temperature Correct answer.

Explanation

The saturation curve shows the boiling or condensing pressure corresponding to each temperature for a pure refrigerant. Inside the saturation dome, liquid and vapour exist together in equilibrium. Technicians use this relationship to determine evaporating and condensing temperatures from gauge readings.

Question 28Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

What are the four basic components found in a typical vapour compression refrigeration circuit?

  1. Compressor, condenser, expansion device and evaporator Correct answer.
  2. Compressor, filter, accumulator and sight glass
  3. Boiler, pump, radiator and fan coil
  4. Absorber, generator, rectifier and reservoir

Explanation

Every vapour compression system relies on four essential components: the compressor, condenser, expansion device and evaporator. These components work together to move refrigerant through the four stages of the cycle. Accessories such as filters and accumulators are helpful additions but are not part of the fundamental cycle.

Question 29Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

Which refrigerant safety classification indicates the lowest hazard in terms of toxicity and flammability?

  1. B1
  2. A1 Correct answer.
  3. A3
  4. B2

Explanation

In the ASHRAE classification, the letter indicates toxicity (A lower than B) and the number indicates flammability (1 lowest, 3 highest). Therefore A1 represents the least toxic and least flammable group. B-class refrigerants carry a higher toxicity hazard, and higher numbers indicate greater flammability.

Question 30Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

What is meant by the term superheat at the evaporator outlet?

  1. The number of degrees the vapour is above its saturation temperature Correct answer.
  2. The number of degrees the liquid is below its saturation temperature
  3. The total heat content of the refrigerant vapour
  4. The pressure drop across the evaporator coil

Explanation

Superheat is the temperature difference between the actual vapour temperature and the saturation temperature at the same pressure. It confirms that all liquid has boiled off before the vapour reaches the compressor. Measuring superheat helps technicians set the expansion device correctly.

Question 31Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

Why does the condenser in an air-cooled refrigeration system reject heat to the surrounding air?

  1. The condenser removes moisture from the refrigerant vapour
  2. The refrigerant vapour is colder than the ambient air, so heat flows into the refrigerant
  3. The condenser creates cold by expanding the refrigerant
  4. The refrigerant vapour is hotter than the ambient air, so heat flows from the refrigerant to the air Correct answer.

Explanation

Heat always flows from a warmer body to a cooler one. The compressor raises the vapour temperature above ambient, allowing the condenser to reject heat and condense the refrigerant. This is why adequate airflow across the coil is essential for efficient operation.

Question 32Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

What happens to the boiling point of a refrigerant as its pressure increases?

  1. The boiling point decreases
  2. The boiling point increases Correct answer.
  3. The boiling point stays exactly the same
  4. The boiling point becomes undefined

Explanation

For any pure refrigerant, saturation temperature rises as saturation pressure rises. This relationship is the basis of the pressure-temperature chart used throughout the trade. It explains why the evaporator operates at low pressure and the condenser at high pressure.

Question 33Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

A gauge reads a suction pressure of 300 kPa for R134a. Using a pressure-temperature chart, the saturation temperature is approximately 0 degrees Celsius. If the measured suction line temperature is 6 degrees Celsius, what is the superheat?

  1. 6 K Correct answer.
  2. 0 K
  3. 18 K
  4. 300 K

Explanation

Superheat is the measured vapour temperature minus the saturation temperature at the same pressure. Here 6 degrees Celsius minus 0 degrees Celsius equals 6 K. The pressure value itself is not part of the subtraction, only the saturation temperature it corresponds to.

Question 34Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

A condenser has a saturation temperature of 45 degrees Celsius and the liquid line measures 40 degrees Celsius. What is the subcooling?

  1. 5 K Correct answer.
  2. 45 K
  3. 40 K
  4. 85 K

Explanation

Subcooling is the saturation temperature minus the actual liquid temperature. Subtracting 40 from 45 gives 5 K of subcooling. This value confirms that the refrigerant has fully condensed and cooled below its saturation point before leaving the condenser.

Question 35Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

Which of the following best describes the state of the refrigerant entering the expansion device in a properly operating system?

  1. Saturated low-pressure liquid
  2. Superheated high-pressure vapour
  3. Superheated low-pressure vapour
  4. Subcooled high-pressure liquid Correct answer.

Explanation

Before the expansion device, the refrigerant should be fully condensed and slightly subcooled to ensure no flash gas enters the valve. This high-pressure liquid then passes through the restriction and drops in pressure and temperature. Subcooling at this point improves valve performance and system capacity.

Question 36Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

Why is a mixture of air and refrigerant vapour in a system undesirable?

  1. Air acts as a lubricant for the compressor
  2. Air lowers the condensing pressure and reduces compressor load
  3. Air is non-condensable and raises head pressure and discharge temperature Correct answer.
  4. Air improves the heat transfer in the condenser

Explanation

Non-condensable gases such as air collect in the condenser and take up space that should be occupied by refrigerant vapour. This raises the condensing pressure and discharge temperature, reducing efficiency and increasing compressor load. Air must therefore be purged from the system.

Question 37Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

A technician measures an evaporator saturation temperature of 2 degrees Celsius and a suction line temperature of 2 degrees Celsius. What does this indicate?

  1. High subcooling at the condenser
  2. Correct superheat for a typical system
  3. Zero superheat, so liquid may be reaching the compressor Correct answer.
  4. Excessive superheat, so the system is undercharged

Explanation

When the suction line temperature equals the saturation temperature, superheat is zero, meaning the refrigerant is still saturated vapour and possibly carrying liquid droplets. Liquid entering a compressor can cause slugging and mechanical damage. A small positive superheat is normally required to protect the compressor.

Question 38Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

Which property of a refrigerant determines how much heat it can absorb per kilogram during evaporation?

  1. Density of the liquid
  2. Latent heat of vaporisation Correct answer.
  3. Ozone depletion potential
  4. Dielectric strength

Explanation

The latent heat of vaporisation is the energy absorbed when one kilogram of liquid becomes vapour. A higher latent heat means more cooling effect per kilogram circulated. Density, dielectric strength and ozone depletion potential describe other characteristics unrelated to heat absorption.

Question 39Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

In an operating system, the evaporating pressure is 200 kPa and the condensing pressure is 1200 kPa. What is the pressure ratio?

  1. 1400
  2. 5
  3. 0.17
  4. 6 Correct answer.

Explanation

Pressure ratio is the absolute condensing pressure divided by the absolute evaporating pressure. Using the given values, 1200 divided by 200 equals 6. A high ratio increases discharge temperature and reduces volumetric efficiency, so it is an important indicator of system performance.

Question 40Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

What is the function of the evaporator in a refrigeration cycle?

  1. To reject heat to the outside air as the refrigerant condenses
  2. To increase the refrigerant pressure before condensation
  3. To store liquid refrigerant during low-load periods
  4. To absorb heat from the refrigerated space as the refrigerant boils Correct answer.

Explanation

The evaporator is where low-pressure liquid refrigerant boils and absorbs heat from the surrounding space or product. This absorbed latent heat produces the cooling effect. The condenser, by contrast, rejects heat, and the compressor raises pressure.

Question 41Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

Why must refrigerant oil be compatible with the refrigerant used in a system?

  1. To reduce the electrical current drawn by the compressor
  2. To raise the condensing pressure for better heat rejection
  3. To increase the cooling capacity of the evaporator
  4. To ensure oil returns to the compressor and maintains adequate lubrication throughout the circuit Correct answer.

Explanation

Oil must remain miscible or sufficiently mobile with the refrigerant so it circulates and returns to the compressor. Poor compatibility can cause oil logging in the evaporator and lead to compressor wear. Lubrication and oil return are the key concerns, not cooling capacity or pressure control.

Question 42Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

A refrigerant cylinder is stored in a hot workshop. What risk does this present?

  1. The pressure inside the cylinder rises, increasing the risk of rupture Correct answer.
  2. The refrigerant changes into a solid and blocks the valve
  3. The refrigerant becomes non-flammable and safe to vent
  4. The cylinder pressure falls and the refrigerant cannot be used

Explanation

Refrigerant cylinders contain liquid under pressure, and heating raises that pressure according to the saturation relationship. Excessive pressure can rupture the cylinder, so cylinders should be stored cool and upright. Never heat a cylinder with an open flame or store it in direct sun.

Question 43Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

Which of the following is an example of sensible heat transfer?

  1. Melting ice at 0 degrees Celsius
  2. Condensing refrigerant vapour in a condenser
  3. Boiling refrigerant in an evaporator
  4. Cooling a room's air from 25 degrees Celsius to 20 degrees Celsius Correct answer.

Explanation

Sensible heat transfer changes the temperature of a substance without a change of state. Cooling air from 25 to 20 degrees Celsius is purely a temperature change. Melting, boiling and condensing all involve latent heat at constant temperature.

Question 44Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

What does a zero reading on a gauge manifold's low-side gauge, with the system running, most likely indicate?

  1. The system has lost its refrigerant charge or the valve is not connected Correct answer.
  2. The system is operating at peak efficiency
  3. The condenser is oversized for the load
  4. The refrigerant is fully subcooled

Explanation

A running system should show a positive suction pressure corresponding to the evaporating temperature. A zero reading suggests no refrigerant is present or the gauge is not properly connected to the service port. The technician should check the connection and look for leaks before adding refrigerant.

Question 45Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

Why is R410A classified as a zeotropic blend requiring liquid charging?

  1. Its components have different boiling points, so vapour charging would change the mixture Correct answer.
  2. It is an azeotrope that behaves exactly like a pure fluid
  3. It is a single pure compound with a fixed boiling point
  4. It contains only one refrigerant and no lubricant

Explanation

R410A is a near-azeotropic blend of R32 and R125 with slightly different boiling points, so its composition can shift if vapour is drawn from a cylinder. Charging as liquid from the cylinder maintains the intended blend ratio. This temperature glide is small but significant enough to require careful charging practice.

Question 46Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

A system shows high superheat at the evaporator outlet and low suction pressure. Which fault is most consistent with these readings?

  1. An overcharge of refrigerant
  2. A condenser fan failure
  3. Excessive subcooling at the liquid line
  4. An undercharge of refrigerant or a restricted expansion device Correct answer.

Explanation

High superheat with low suction pressure indicates the evaporator is starved of refrigerant, often because of undercharging or a restriction at the expansion device. The reduced mass flow boils off early and the vapour becomes excessively superheated. Overcharging and condenser faults typically produce high head pressure rather than these symptoms.

Question 47Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

In a system using a thermostatic expansion valve, what happens if the sensing bulb loses its charge?

  1. The valve opens fully and floods the evaporator
  2. The valve reverses refrigerant flow through the circuit
  3. The valve maintains its last set position indefinitely
  4. The valve tends to remain closed, starving the evaporator Correct answer.

Explanation

The bulb charge exerts opening force on the valve diaphragm, balanced against evaporator pressure and spring force. If the bulb loses charge, the opening force disappears and the spring closes the valve, starving the evaporator. Symptoms include low suction pressure and high superheat.

Question 48Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

Why does a higher condensing temperature reduce the efficiency of a vapour compression cycle?

  1. The evaporator absorbs more heat at higher condensing temperature
  2. The compressor must work against a greater pressure difference, increasing energy input per unit of cooling Correct answer.
  3. The refrigerant latent heat increases sharply at higher condensing temperature
  4. The expansion device bypasses more refrigerant at higher condensing temperature

Explanation

Raising the condensing temperature raises the discharge pressure, so the compressor must compress across a larger pressure difference. This increases the work input for each kilogram of refrigerant circulated and lowers the coefficient of performance. Keeping condensers clean and well ventilated minimises this penalty.

Question 49Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

A technician finds frost forming only at the inlet of the evaporator while the rest of the coil is warm, with low suction pressure. What is the most likely cause?

  1. A failed condenser fan motor
  2. Too much superheat at the compressor
  3. A restriction in the expansion device or distributor Correct answer.
  4. An overcharge of refrigerant

Explanation

A restriction limits refrigerant flow so that only the first part of the coil gets cold enough to frost, while the remainder starves and stays warm. Low suction pressure and high superheat accompany this pattern. An overcharge or condenser fault would instead raise head pressure.

Question 50Refrigeration and Air Conditioning Fundamentals (Thermodynamics, Pressure-Temperature, Refrigerants)

In a vapour compression refrigeration cycle, which component is responsible for raising the pressure and temperature of the refrigerant vapour?

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

Explanation

The compressor is the heart of the cycle; it draws low-pressure vapour from the evaporator and compresses it to a higher pressure, which also raises its temperature. This high-pressure, high-temperature vapour then flows to the condenser where it rejects heat. The other components handle heat transfer or expansion, not compression.