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Red Seal Refrigeration & AC Mechanic study materials
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Red Seal Refrigeration & AC Mechanic practice questions

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Question 1Occupational health and safety, and environmental protection

Under WHMIS 2018, which document must accompany a hazardous refrigerant cylinder shipped into a Canadian workplace, and what information does it convey?

  1. A transport log recording the cylinder's pressure during delivery
  2. A Safety Data Sheet providing hazard classification, handling, and first-aid information Correct answer.
  3. A purchase invoice confirming the cylinder was bought from an approved supplier
  4. A calibration certificate proving the refrigerant meets purity standards

Explanation

WHMIS 2018 requires suppliers to provide a Safety Data Sheet (SDS) with each hazardous product, including refrigerants. The SDS communicates hazard classification, safe handling, PPE, first aid, and emergency measures so workers can protect themselves.

Question 2Occupational health and safety, and environmental protection

A technician must recover refrigerant from a small residential split system before opening the circuit. Which practice best reflects the environmental and safety requirements of the task?

  1. Discharge the refrigerant into a bucket of water to dissolve it before disposal
  2. Release the charge while the system runs so the compressor pumps it out faster
  3. Vent the charge slowly to atmosphere to avoid overpressurizing the recovery cylinder
  4. Use certified recovery equipment and store the recovered refrigerant in a properly labeled cylinder Correct answer.

Explanation

Refrigerant must be recovered with certified equipment and held in a DOT/TC-approved, properly labeled cylinder for recycling, reclamation, or destruction. Deliberate venting is prohibited because refrigerants deplete ozone or contribute to global warming and can displace oxygen in confined spaces.

Question 3Occupational health and safety, and environmental protection

Which personal protective equipment is most important when there is a risk of liquid refrigerant contacting the skin or eyes during a service procedure?

  1. A respirator with organic vapor cartridges and nitrile exam gloves
  2. Insulated work gloves and a dust mask
  3. A face shield over safety glasses and cotton work gloves
  4. Chemical splash goggles and insulated, refrigerant-resistant gloves Correct answer.

Explanation

Liquid refrigerant can cause frostbite and severe eye damage, so the primary protection is splash-rated eye protection plus gloves that resist the refrigerant and insulate against cold. Standard cotton or exam gloves do not protect against rapid evaporative freezing.

Question 4Occupational health and safety, and environmental protection

A recovery cylinder is filled with recovered R-410A. Which combination of markings and precautions is required before the cylinder is stored or transported?

  1. Marked as empty and stored upright in a warm area
  2. Labeled with the refrigerant type and 'recovered refrigerant,' never overfilled, and kept below its pressure rating Correct answer.
  3. Painted gray to match the system and stored horizontally to save space
  4. Labeled only with the date of recovery and the technician's initials

Explanation

Recovery cylinders must be identified by refrigerant type and clearly marked as containing recovered refrigerant. They must never be overfilled, because liquid expansion with temperature rise can exceed the cylinder's pressure rating and rupture it.

Question 5Occupational health and safety, and environmental protection

Which statement correctly describes the hazard posed by a refrigerant leak in a small, poorly ventilated mechanical room?

  1. Refrigerant leaks will always be detected by smell before the concentration becomes dangerous
  2. Refrigerants can displace oxygen and cause asphyxiation, so the space must be ventilated before entry Correct answer.
  3. Refrigerant vapors are heavier than air and will always exit through the ceiling
  4. Refrigerants are harmless at low concentration and require no entry precautions

Explanation

Many refrigerants are denser than air and can accumulate in low areas, displacing oxygen and creating an asphyxiation risk. Ventilating the space and using gas detection before entry protects the technician from entering an oxygen-deficient atmosphere.

Question 6Occupational health and safety, and environmental protection

A technician is brazing copper lines near a wall covered with combustible insulation. Which control best prevents ignition of the surrounding material?

  1. Open a window to dilute combustion gases in the room
  2. Turn off the vacuum pump before lighting the torch
  3. Wear leather gloves and a welding helmet during the brazing
  4. Wet down the area, use a heat shield or fire blanket, and keep a fire extinguisher within reach Correct answer.

Explanation

Hot-work controls focus on preventing ignition of combustibles: remove or shield combustible material, wet down the area, and have firefighting equipment immediately available. Ventilation and PPE reduce exposure but do not prevent ignition of nearby materials.

Question 7Occupational health and safety, and environmental protection

Which of the following best describes the required response when a refrigerant monitor alarms in a machinery room containing a large ammonia system?

  1. Open the nearest valve to relieve pressure and dilute the leak
  2. Ignore the alarm until a second sensor confirms the reading
  3. Continue work and reset the alarm if the reading is below the upper explosive limit
  4. Evacuate the space, ventilate, and investigate only with appropriate respiratory protection Correct answer.

Explanation

Ammonia is toxic and flammable, so an alarm requires evacuation, ventilation, and investigation by personnel wearing the appropriate respiratory protection. Never reset or override an alarm without identifying and correcting the source.

Question 8Occupational health and safety, and environmental protection

When handling a refrigerant cylinder in cold weather, a technician notices frost on the valve and the cylinder feels unusually cold. What is the safest course of action?

  1. Warm the cylinder gradually in a controlled manner and never exceed the cylinder's rated pressure Correct answer.
  2. Submerge the cylinder in hot water to speed vaporization
  3. Roll the cylinder to agitate the liquid and increase pressure
  4. Heat the cylinder with an open flame torch to raise pressure quickly

Explanation

Cylinders must never be heated with an open flame or by immersion in hot water, since rapid pressure rise can rupture them. Gradual, controlled warming that stays within the cylinder's rated pressure is the safe approach.

Question 9Occupational health and safety, and environmental protection

A technician is preparing to open a refrigerant circuit that has been confirmed empty. Which additional step protects against residual pressure and moisture ingress?

  1. Flush the lines with water and dry them with a heat gun
  2. Pull and hold a vacuum to confirm no residual pressure or leaks, then break the vacuum with dry nitrogen Correct answer.
  3. Purge the lines with compressed shop air before brazing
  4. Loosen the flare nut slowly to vent any remaining gas to the room

Explanation

After recovery, pulling a vacuum confirms the circuit is empty and leak-free, and breaking the vacuum with dry nitrogen prevents moisture and air from entering. Compressed shop air and water introduce contaminants that damage the system.

Question 10Occupational health and safety, and environmental protection

Which regulation primarily governs the safe transportation of a filled refrigerant cylinder by road in Canada?

  1. The National Building Code of Canada
  2. The Canada Labour Code, Part II only
  3. The Transportation of Dangerous Goods Act and Regulations Correct answer.
  4. The Canadian Electrical Code

Explanation

The Transportation of Dangerous Goods Act and Regulations set requirements for classification, packaging, marking, labeling, and documentation of dangerous goods in transport, including pressurized refrigerant cylinders. Workplace safety legislation covers the workplace but not the transport requirements.

Question 11Occupational health and safety, and environmental protection

A technician finds a small leak in a system containing an ozone-depleting refrigerant. Which action best complies with environmental regulations?

  1. Replace the refrigerant with a different type without recovering the original charge
  2. Seal the leak with tape and recharge the system
  3. Repair the leak, recover the refrigerant, and document the recovery before recharging Correct answer.
  4. Top up the charge and schedule the repair for the next service visit

Explanation

Regulations require leaks in ozone-depleting systems to be repaired and refrigerant to be recovered rather than released. Documentation of recovery supports compliance and traceability of the refrigerant.

Question 12Occupational health and safety, and environmental protection

Which practice is required when using nitrogen to pressure-test a refrigeration system?

  1. Use a regulator and relief valve, and never exceed the test pressure rating of the lowest-rated component Correct answer.
  2. Connect the nitrogen cylinder directly to the system without a regulator
  3. Leave the system pressurized overnight without marking or barricading the area
  4. Pressurize the system with oxygen to speed the test

Explanation

A pressure regulator and relief valve protect the system and personnel by limiting test pressure to the rating of the weakest component. Nitrogen is the correct inert test gas; oxygen is never used because it supports combustion and contaminates the system.

Question 13Occupational health and safety, and environmental protection

A technician is working alone in a remote plant room when a large refrigerant release occurs. Which combination of controls best reflects an acceptable lone-worker procedure?

  1. Rely on a personal cell phone with no check-in schedule
  2. Use a check-in system with a designated contact and carry a gas monitor and escape respirator Correct answer.
  3. Lock the door so no one can interrupt the work
  4. Postpone all communication until the task is finished

Explanation

Lone-worker procedures require a check-in system with a designated contact plus equipment appropriate to the hazard, such as a gas monitor and escape respiratory protection. A cell phone alone without a check-in schedule does not provide reliable monitoring.

Question 14Occupational health and safety, and environmental protection

In a system using a flammable refrigerant classified A3, which precaution is most critical during service?

  1. Charge the system in a closed room to prevent refrigerant from escaping
  2. Use standard recovery equipment without checking its compatibility with flammable refrigerants
  3. Eliminate ignition sources, ventilate the area, and use leak detection rated for flammable refrigerants Correct answer.
  4. Use an open-flame leak detector to locate the leak quickly

Explanation

A3 refrigerants are flammable, so service requires eliminating ignition sources, ventilating the space, and using detection and recovery equipment rated for flammable refrigerants. Open flames and enclosed charging areas create an unacceptable fire or explosion risk.

Question 15Occupational health and safety, and environmental protection

A technician must dispose of a recovered refrigerant that is contaminated with moisture and acid. Which option best meets environmental and legal obligations?

  1. Blend it with virgin refrigerant and return it to the customer's system
  2. Vent it slowly outdoors over several hours
  3. Send it to a certified reclamation facility or approved destruction service and retain the documentation Correct answer.
  4. Store it indefinitely in an unlabeled cylinder in the shop yard

Explanation

Contaminated refrigerant must be sent to a certified reclamation facility or an approved destruction service, with documentation retained to demonstrate compliance. Blending, venting, or unlabeled storage violates environmental requirements and creates hazards.

Question 16Occupational health and safety, and environmental protection

A technician is assessing the risk of retrofitting an existing R-22 system to a newer refrigerant blend. Which factor most directly affects the safety of the retrofit?

  1. The compatibility of the new blend with existing elastomers, lubricants, and system pressure ratings Correct answer.
  2. The age of the customer's thermostat
  3. The brand of the manifold gauge set used during charging
  4. The color of the existing suction line insulation

Explanation

A retrofit changes the operating pressure, lubricant compatibility, and material compatibility of the system, so these factors determine whether components and seals can safely handle the new blend. Cosmetic or tool-brand factors do not affect system safety.

Question 17Tools, equipment, and shop practices

When leak-testing a refrigeration system with dry nitrogen, which regulator setup is required on the nitrogen cylinder?

  1. A nitrogen regulator designed for the cylinder pressure, with a relief valve set to protect the system Correct answer.
  2. An oxygen regulator fitted with a flowmeter and check valve
  3. A nitrogen regulator with a relief valve and rated working pressure below the low-side design pressure
  4. A direct cylinder-to-manifold connection with a ball valve and pressure gauge

Explanation

Nitrogen cylinders deliver very high pressure, so a dedicated nitrogen regulator is required to reduce it to a safe test pressure. The regulator must have a relief valve so that overpressure cannot damage the system being tested. Oxygen regulators and direct connections are unsafe because they cannot reliably limit pressure.

Question 18Tools, equipment, and shop practices

A technician must cut and re-flare a 3/8 in. copper line on a split system. Which tool combination produces the correct 45-degree flare for a SAE flare nut?

  1. A hacksaw, deburring tool, and a swaging punch set
  2. A tubing cutter and a 37-degree flaring tool
  3. A tubing cutter, reamer, and a flaring block with the correct-size yoke Correct answer.
  4. A pipe cutter and a compression fitting wrench

Explanation

SAE flare joints on refrigeration copper require a square cut, a reamed and deburred end, and a 45-degree flare formed in a flaring block of the correct size. A tubing cutter and reamer give a clean, round end so the flare seats without cracks. The flaring yoke must match the tube diameter to produce the correct flare diameter.

Question 19Tools, equipment, and shop practices

Which instrument is the correct choice for measuring the superheat at the evaporator outlet of an operating system?

  1. An infrared thermometer aimed at the suction line
  2. A clamp-on thermocouple or contact thermometer on the suction line plus a calibrated low-side gauge Correct answer.
  3. A hygrometer placed at the return grille
  4. A digital multimeter with a temperature probe in the airstream

Explanation

Superheat is the difference between the actual suction line temperature and the saturated suction temperature at the same pressure. That requires an accurate line temperature reading at the evaporator outlet and a calibrated low-side pressure reading. The two values are then converted to superheat using a pressure-temperature chart.

Question 20Tools, equipment, and shop practices

What is the primary purpose of a vacuum pump with a gas ballast feature during evacuation of a refrigeration system?

  1. To purge non-condensables from the discharge line automatically
  2. To allow the pump to reach a deeper ultimate vacuum than a two-stage pump
  3. To increase the pumping speed for large-diameter lines
  4. To prevent moisture vapor from condensing in the pump oil during the initial pull-down Correct answer.

Explanation

During the early stages of evacuation, water vapor can condense in the pump oil and degrade the vacuum. The gas ballast admits a small amount of air to keep the vapor from condensing in the compression stroke. This protects the oil and helps the pump remove moisture-laden vapor more effectively.

Question 21Tools, equipment, and shop practices

Which personal protective equipment is essential when using a caustic-based coil cleaner on an evaporator coil?

  1. Hearing protection and a face shield only
  2. A dust mask and cotton gloves
  3. Safety glasses only, because the cleaner is diluted
  4. Chemical splash goggles, acid-resistant gloves, and an apron or long sleeves Correct answer.

Explanation

Caustic coil cleaners can cause severe chemical burns and eye damage, so splash goggles, chemical-resistant gloves, and body protection are required. Manufacturer safety data sheets specify the exact PPE for each product. Dilution does not remove the hazard.

Question 22Tools, equipment, and shop practices

A technician is brazing a suction line and notices the joint is not drawing filler into the cup. Which practice most likely explains the failure?

  1. The joint was heated until the base metal reached brazing temperature before filler was applied
  2. The filler was applied while the joint was still below the flow temperature of the alloy Correct answer.
  3. The nitrogen purge was started before the torch was lit
  4. The tubing was cleaned and fluxed before heating

Explanation

Brazing filler flows by capillary action only when the base metal reaches the alloy's working temperature. Applying filler to a cold joint causes it to ball up and sit on the surface instead of drawing into the cup. The correct technique is to heat the joint evenly and touch the filler to the joint, letting the base metal melt it.

Question 23Tools, equipment, and shop practices

A manifold gauge set reads 0 psig on both the high and low sides with the system running and the compressor energized. Which diagnostic step is most appropriate?

  1. Check for a completely closed service valve or a restriction between the gauge port and the system Correct answer.
  2. Add refrigerant immediately to bring the low side up
  3. Increase the condenser airflow to lower the head pressure
  4. Replace the compressor because it has failed internally

Explanation

Equal zero readings on both gauges usually mean the gauges are isolated from the system, such as by closed service valves or a blocked port. The technician should verify that the manifold hoses and valves are actually open to the system before diagnosing the refrigeration circuit. Adding refrigerant or replacing parts based on an invalid reading risks damage and misdiagnosis.

Question 24Tools, equipment, and shop practices

When using a recovery machine to transfer refrigerant from a system into a recovery cylinder, which practice is required?

  1. Fill the recovery cylinder to no more than 80 percent of its capacity by weight Correct answer.
  2. Fill the cylinder until the pressure equalizes with the system
  3. Use a cylinder marked for refrigerant service regardless of its test date
  4. Recover the refrigerant as a liquid only, never as a vapor

Explanation

Recovery cylinders must never be filled beyond about 80 percent of their water capacity to leave room for liquid expansion. Overfilling can lead to hydrostatic pressure buildup and cylinder rupture. Filling is controlled by weight using a scale, not by pressure equalization.

Question 25Tools, equipment, and shop practices

A technician is selecting a vacuum gauge for system evacuation. Which instrument provides the most accurate indication of deep vacuum?

  1. A compound gauge on the manifold set
  2. A digital micron gauge connected directly to the system Correct answer.
  3. A pressure transducer on the high side
  4. A thermocouple vacuum gauge installed on the pump inlet

Explanation

A digital micron gauge connected directly to the system, with a short large-diameter hose and no manifold in the path, gives the most accurate deep-vacuum reading. Manifold compound gauges cannot resolve micron-level pressures. Direct connection avoids the pressure drop and contamination that skew readings.

Question 26Tools, equipment, and shop practices

Which procedure correctly leak-tests a brazed joint on a newly installed line set before evacuation?

  1. Pressurize with compressed shop air and listen for hissing
  2. Pressurize with refrigerant and check with a halide torch
  3. Pressurize with dry nitrogen to the manufacturer's test pressure, then check joints with an electronic leak detector or soap bubbles Correct answer.
  4. Pull a vacuum and watch the micron gauge for a rise

Explanation

Dry nitrogen is the preferred test gas because it is dry, inert, and leaves no residue in the system. The system is pressurized to the manufacturer's specified test pressure and joints are checked with an electronic detector or soap solution. Refrigerant should not be used solely as a test gas because of environmental and cost concerns.

Question 27Tools, equipment, and shop practices

A technician is measuring superheat on a TXV system and reads a suction pressure of 68 psig (R-410A, saturation about 40°F) and a suction line temperature of 52°F. What is the superheat?

  1. 12°F Correct answer.
  2. 40°F
  3. 92°F
  4. 52°F

Explanation

Superheat equals the suction line temperature minus the saturated suction temperature at the measured pressure. Using the values given, 52°F minus 40°F equals 12°F. This falls within a typical target range for many TXV systems, though the manufacturer's charging chart should always be consulted.

Question 28Tools, equipment, and shop practices

A technician needs to measure the operating current of a hermetic compressor to compare against the nameplate RLA. Which meter setup is correct?

  1. An ohmmeter connected across the run capacitor
  2. A voltmeter connected across the compressor terminals
  3. A wattmeter connected in parallel with the contactor coil
  4. A clamp-on ammeter placed around one of the compressor supply conductors Correct answer.

Explanation

A clamp-on ammeter placed around a single supply conductor measures the current drawn by the compressor without breaking the circuit. The reading is compared with the nameplate rated load amps to assess loading. Voltmeters and ohmmeters measure different quantities and cannot indicate running current.

Question 29Tools, equipment, and shop practices

A technician is preparing to braze a joint on a system that contains refrigerant. Which practice best protects the system and the technician?

  1. Brazing directly on the pressurized line to save time
  2. Purging with refrigerant vapor during brazing to prevent oxidation
  3. Opening the line and brazing while the compressor continues to run
  4. Recovering the refrigerant, breaking the vacuum with dry nitrogen, and brazing with a nitrogen purge Correct answer.

Explanation

Brazing a pressurized or refrigerant-containing line can cause a pressure rise, decomposition of refrigerant into toxic compounds, and a fire hazard. The refrigerant must be recovered, and the line should be purged with dry nitrogen during brazing to prevent internal oxidation. This protects both the system and the technician.

Question 30Tools, equipment, and shop practices

A technician is setting up a system for evacuation and wants to minimize the time to reach 500 microns. Which combination of practices is most effective?

  1. Use a single small hose connected to the high side only
  2. Use a manifold with the valves cracked open and a micron gauge on the pump inlet
  3. Use the largest-diameter, shortest hoses possible, remove Schrader cores, and connect the micron gauge directly to the system Correct answer.
  4. Use standard charging hoses through the manifold and rely on the compound gauge

Explanation

Evacuation speed is limited by the conductance of the path between the system and the pump. Large-diameter, short hoses with the Schrader cores removed minimize restriction, and a micron gauge connected directly to the system measures the actual system vacuum. Together these practices reduce evacuation time and improve accuracy.

Question 31Tools, equipment, and shop practices

A technician observes that a digital manifold reads a suction pressure that differs from a separate calibrated gauge by 8 psig. What is the most appropriate action before charging the system?

  1. Add refrigerant until the two gauges agree
  2. Replace the system's suction service valve
  3. Recalibrate or verify the digital manifold against a known reference and use the verified instrument Correct answer.
  4. Average the two readings and proceed

Explanation

Charging decisions depend on accurate pressure readings, so a discrepancy must be resolved before proceeding. The digital manifold should be checked against a known reference or recalibrated according to the manufacturer's procedure. Only a verified instrument should be used to determine superheat or subcooling.

Question 32Tools, equipment, and shop practices

Which practice is correct when storing and handling recovery cylinders in the shop?

  1. Store upright, secured, away from heat, and with valves closed and caps installed Correct answer.
  2. Store near the brazing station for convenience
  3. Store horizontally to save floor space
  4. Store with valves open to relieve pressure buildup

Explanation

Recovery cylinders should be stored upright and secured to prevent tipping, away from heat sources, with valves closed and protective caps installed. These practices prevent damage to the valve and uncontrolled release. Cylinders should also be within their hydrostatic test date.

Question 33Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

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

  1. It absorbs heat from the refrigerated space to boil the refrigerant
  2. It meters refrigerant flow into the evaporator to maintain superheat
  3. It rejects latent and sensible heat from the high-pressure refrigerant to the ambient medium Correct answer.
  4. It raises the refrigerant pressure from evaporator pressure to discharge pressure

Explanation

The condenser is the heat-rejection component: desuperheated vapour is first cooled, then condensed at essentially constant pressure, and finally subcooled before it leaves. The heat removed equals the sum of the heat absorbed in the evaporator plus the work of compression, which is why condenser load always exceeds evaporator load.

Question 34Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

A technician measures 12 °C superheat at the evaporator outlet. Which statement best describes the condition of the refrigerant at that point?

  1. It is superheated vapour at the compressor discharge pressure
  2. It is subcooled liquid 12 K below its saturation temperature
  3. It is a saturated liquid-vapour mixture at evaporator pressure
  4. It is vapour at a temperature 12 K above its saturation temperature for that pressure Correct answer.

Explanation

Superheat is the difference between the actual vapour temperature and the saturation temperature corresponding to the same pressure. A reading of 12 K confirms that all liquid has boiled off and the vapour has gained a further 12 K of sensible heat beyond saturation.

Question 35Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

Which of the following correctly states the second law of thermodynamics as it applies to a refrigeration machine?

  1. The total energy of an isolated system always decreases during a cycle
  2. The entropy of a system always increases during an isentropic compression
  3. Heat flows spontaneously from a colder body to a hotter body without work input
  4. Heat cannot be transferred from a lower-temperature region to a higher-temperature region without work input Correct answer.

Explanation

The second law establishes the direction of spontaneous heat flow and requires external work to move heat against a temperature gradient. That requirement is the entire reason a compressor is needed in a refrigeration cycle.

Question 36Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

In a direct-expansion coil operating normally, the refrigerant leaving the evaporator should be:

  1. Slightly superheated vapour Correct answer.
  2. Subcooled liquid
  3. A saturated liquid-vapour mixture at roughly 50 percent quality
  4. Two-phase mixture with a small amount of liquid carryover

Explanation

The expansion valve is set so that complete evaporation occurs before the coil outlet, leaving a small margin of superheat. This protects the compressor from liquid slugging while still using most of the coil surface for latent heat transfer.

Question 37Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

What does a coefficient of performance (COP) of 3.5 for a refrigeration system mean?

  1. The system removes 3.5 kJ of heat per kilogram of refrigerant circulated
  2. The system rejects 3.5 times more heat at the condenser than it absorbs at the evaporator
  3. The system removes 3.5 kW of heat for every kilowatt of compressor power Correct answer.
  4. The system achieves 3.5 percent of the theoretical Carnot efficiency

Explanation

COP is a dimensionless ratio of useful cooling effect to net work input, so a value of 3.5 means 3.5 units of heat are removed per unit of compressor energy. It is not a mass-specific quantity nor a percentage of Carnot efficiency.

Question 38Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

Which pressure-enthalpy diagram feature represents the work of compression per unit mass?

  1. The horizontal distance between evaporator and condenser pressures
  2. The vertical distance between the saturated vapour line and the critical point
  3. The enthalpy difference between saturated liquid and saturated vapour at the evaporator
  4. The enthalpy difference between compressor suction and discharge Correct answer.

Explanation

On a P-h diagram, work input appears as the increase in enthalpy across the compressor at constant entropy for an ideal machine. That horizontal enthalpy difference, multiplied by mass flow, gives total compressor power.

Question 39Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

Which statement about sensible heat is correct?

  1. It equals the latent heat of vaporisation for the substance
  2. It is absorbed or released with a change of state at constant temperature
  3. It is absorbed or released with a change in temperature but no change of state Correct answer.
  4. It can only be transferred by radiation

Explanation

Sensible heat changes the temperature of a substance without altering its phase, as when air is warmed across a heating coil. Latent heat, by contrast, is associated with phase change at constant temperature.

Question 40Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

Air at 24 °C dry-bulb and 50 percent relative humidity is cooled sensibly to 18 °C. What happens to its relative humidity?

  1. It stays the same because no moisture was added or removed
  2. It decreases because the dry-bulb temperature falls
  3. It increases because the saturation vapour pressure at the lower temperature is smaller Correct answer.
  4. It cannot be determined without knowing the barometric pressure

Explanation

Sensible cooling at constant moisture content lowers the dry-bulb temperature, which reduces the saturation vapour pressure. Since the actual vapour pressure is unchanged, the ratio of actual to saturation pressure, and therefore relative humidity, rises.

Question 41Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

A system using R-410A has a suction pressure corresponding to a saturation temperature of 5 °C and a measured suction line temperature of 11 °C. What is the superheat?

  1. 11 K
  2. 6 K Correct answer.
  3. 5 K
  4. 16 K

Explanation

Superheat is measured line temperature minus the saturation temperature for the same pressure: 11 °C minus 5 °C equals 6 K. The pressure must be converted to its saturation temperature before subtracting, not used directly.

Question 42Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

Why does flash gas forming in the liquid line before the evaporator reduce system capacity?

  1. It increases the latent heat of vaporisation of the refrigerant
  2. It occupies expansion-valve and coil volume that would otherwise carry liquid, lowering the useful refrigerating effect Correct answer.
  3. It raises the evaporator saturation pressure and therefore the coil temperature
  4. It increases the mass of liquid available for boiling in the coil

Explanation

Flash gas is vapour produced by pressure drop or heat gain before the metering device. Vapour contributes almost no cooling in the evaporator, so the effective refrigerating effect per kilogram circulated drops and capacity falls.

Question 43Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

Two identical rooms lose the same heat. Room A is maintained at 20 °C and Room B at 26 °C, with the same outdoor temperature. Which room requires more refrigeration capacity?

  1. Both rooms require the same capacity because the heat loss is stated as equal
  2. Room B, because warmer air holds more moisture
  3. Room A, because the larger temperature difference drives a higher heat gain Correct answer.
  4. Room B, because the evaporator must run at a higher saturation temperature

Explanation

Heat transfer through the envelope is proportional to the temperature difference across it. Holding a space colder increases that difference, so the transmission load and the required capacity are greater even though the spaces are otherwise identical.

Question 44Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

In a psychrometric chart, what does the wet-bulb temperature line approximate?

  1. The line of constant relative humidity
  2. The line of constant specific volume
  3. The line of constant dew point
  4. The line of constant enthalpy and constant moisture content during adiabatic saturation Correct answer.

Explanation

The thermodynamic wet-bulb line closely follows constant enthalpy and constant moisture content for air undergoing adiabatic saturation. That is why wet-bulb and enthalpy scales are often read along the same diagonal direction on the chart.

Question 45Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

A refrigerant enters the compressor as saturated vapour at -10 °C and leaves at 70 °C. Which statement about the compression process is most accurate?

  1. The process is isothermal because the refrigerant changes phase
  2. The process is isobaric and the discharge remains saturated vapour
  3. The process is isenthalpic and the discharge is a liquid-vapour mixture
  4. The process is isentropic and the discharge is superheated vapour Correct answer.

Explanation

Ideal compression is modelled as isentropic, and compressing saturated vapour necessarily produces superheated vapour at the higher discharge pressure. The temperature rise from -10 °C to 70 °C is consistent with that superheat.

Question 46Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

What is the effect of subcooling the liquid leaving the condenser while all other conditions remain the same?

  1. It increases the refrigerating effect per kilogram and improves capacity Correct answer.
  2. It raises the compressor discharge temperature without changing capacity
  3. It increases the mass flow required for a given load
  4. It reduces the refrigerating effect per kilogram and lowers capacity

Explanation

Subcooling lowers the enthalpy of the liquid entering the expansion device, so more heat can be absorbed per kilogram in the evaporator. With the same compressor work, both refrigerating effect and COP improve.

Question 47Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

Which condition causes a thermostatic expansion valve to open wider?

  1. Decreased superheat at the evaporator outlet
  2. Increased superheat at the evaporator outlet Correct answer.
  3. Increased subcooling at the condenser outlet
  4. Increased condenser pressure with constant evaporator load

Explanation

The valve balances bulb pressure against evaporator pressure plus spring force. Rising superheat warms the bulb, raising its pressure and opening the valve to admit more refrigerant until superheat returns to the set point.

Question 48Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

A technician finds frost forming only at the inlet of an evaporator while the rest of the coil is warm. Which diagnosis is most consistent?

  1. The compressor is oversized for the coil
  2. The expansion valve is feeding too little refrigerant, causing starvation Correct answer.
  3. The condenser fan is not running
  4. The system is overcharged with refrigerant

Explanation

A starved coil boils off refrigerant very early, so the inlet section runs cold enough to frost while downstream passes stay warm. The pattern of frost confined to the distributor and first passes is the classic signature of underfeeding.

Question 49Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

Which statement correctly describes the relationship between absolute and gauge pressure in a refrigeration system?

  1. Absolute pressure equals gauge pressure plus atmospheric pressure Correct answer.
  2. Absolute pressure and gauge pressure are numerically identical at sea level
  3. Gauge pressure is measured relative to a perfect vacuum
  4. Gauge pressure equals absolute pressure plus atmospheric pressure

Explanation

Gauge pressure uses atmospheric pressure as its zero reference, so absolute pressure is obtained by adding atmospheric pressure to the gauge reading. This conversion matters whenever a saturation table, which is tabulated in absolute pressure, is used.

Question 50Refrigeration and air conditioning fundamentals (thermodynamics, heat transfer, psychrometrics, system cycles)

Why is a lower condensing temperature desirable in a refrigeration cycle, all else being equal?

  1. It raises the evaporator saturation temperature
  2. It eliminates the need for a metering device
  3. It increases the pressure ratio and improves capacity
  4. It reduces the pressure ratio and compressor work per kilogram Correct answer.

Explanation

A lower condensing pressure reduces the compression ratio, which lowers discharge temperature and specific work. The result is improved COP and reduced compressor power for the same cooling load.