I85PREP
⌘ K
DE HVAC study materials
DE HVAC study resources

DE HVAC practice questions

One question at a time. Build your DE HVAC understanding.

First 50 of 190 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Delaware HVACR authority, scope and examination preparation

Which Delaware state agency regulates HVAC contractor licensing?

  1. Delaware Department of Labor
  2. Delaware Division of Professional Regulation (DPR) Correct answer.
  3. Delaware Department of Safety
  4. Delaware Building Commission

Explanation

The Delaware Division of Professional Regulation (DPR), under the Board of Plumbing, Heating, Ventilation, Air Conditioning and Refrigeration Examiners, oversees all HVACR licensing in Delaware. The DPR administers exams, processes applications, and enforces regulations.

Question 2Delaware HVACR authority, scope and examination preparation

Under Delaware Title 24, which board oversees HVACR examiners?

  1. Board of Electrical Examiners
  2. Board of Plumbing, Heating, Ventilation, Air Conditioning and Refrigeration Examiners Correct answer.
  3. Board of General Contractors
  4. Board of Professional Engineers

Explanation

Delaware Title 24 establishes the Board of Plumbing, Heating, Ventilation, Air Conditioning and Refrigeration Examiners to regulate HVACR professionals. The Board sets exam standards, approves continuing education, and enforces licensing regulations under the Division of Professional Regulation.

Question 3Delaware HVACR authority, scope and examination preparation

What is the proper procedure when a customer requests work outside the contractor's license scope?

  1. Perform the work anyway
  2. Decline the work and recommend a properly licensed professional for that specific trade Correct answer.
  3. Charge extra for the risk
  4. Have an unlicensed helper do it

Explanation

When work falls outside the HVAC contractor's license scope (such as major electrical or plumbing work), the contractor should decline that portion and recommend a properly licensed professional. Performing work outside the license scope violates Delaware law and creates significant liability and safety risks.

Question 4Air conditioning, airflow and accountable installation evidence

What is the purpose of an air-side economizer in a commercial HVAC system in Delaware?

  1. To increase cooling capacity beyond the equipment rating
  2. To use outdoor air for free cooling when outdoor conditions are favorable, reducing compressor runtime Correct answer.
  3. To heat outdoor air in winter
  4. To reduce indoor air quality

Explanation

An air-side economizer can use suitable outdoor air to meet part of the cooling demand when actual temperature, moisture and air-quality conditions permit. Controls and relevant freeze or humidity protections matter. Outdoor air is not always useful cooling, and energy savings are not guaranteed under every condition.

Question 5Air conditioning, airflow and accountable installation evidence

What is the purpose of an energy recovery ventilator (ERV) versus a heat recovery ventilator (HRV)?

  1. They are the same device
  2. An ERV transfers both heat and moisture between air streams, while an HRV transfers only heat Correct answer.
  3. An HRV is more efficient than an ERV
  4. An ERV is only for commercial use

Explanation

An Energy Recovery Ventilator (ERV) transfers both sensible heat and moisture (latent energy) between the exhaust and supply air streams. A Heat Recovery Ventilator (HRV) transfers only sensible heat. ERVs are preferred in humid climates to help control indoor humidity, while HRVs are better in very cold, dry climates.

Question 6Air conditioning, airflow and accountable installation evidence

What is the building envelope and why is it important for HVAC design in Delaware?

  1. The mailing address of the building
  2. The physical barrier between the conditioned interior and unconditioned exterior that determines heating and cooling loads Correct answer.
  3. The architectural design style
  4. The building's fire escape plan

Explanation

The building envelope includes all components separating the conditioned interior from the unconditioned exterior: walls, roof, foundation, windows, doors, and air sealing. In Delaware's climate (hot summers, cold winters), the envelope's insulation levels, window performance, and air tightness directly determine heating and cooling load requirements.

Question 7Air conditioning, airflow and accountable installation evidence

What duct material is commonly used for residential flexible ductwork in Delaware?

  1. Galvanized steel only
  2. Insulated flexible duct with an inner core, fiberglass insulation, and vapor barrier jacket Correct answer.
  3. PVC pipe
  4. Concrete duct

Explanation

Insulated flexible ductwork consisting of a wire-supported inner core, fiberglass insulation (typically R-6 to R-8), and an outer vapor barrier jacket is commonly used for residential branch runs in Delaware. Flex duct must be properly supported, stretched taut, and installed per manufacturer instructions to minimize airflow restriction.

Question 8Air conditioning, airflow and accountable installation evidence

What is the purpose of a condensate neutralizer on a high-efficiency furnace?

  1. To increase furnace efficiency
  2. To raise the pH of acidic condensate before it enters the drain system to protect pipes Correct answer.
  3. To condense more moisture from flue gases
  4. To neutralize odors from the furnace

Explanation

A condensate neutralizer raises the pH of the acidic condensate (typically pH 3-4) produced by high-efficiency condensing furnaces before it enters the drain system. The neutralizer contains limestone or other alkaline media that dissolves slowly to raise the pH, protecting drain pipes from corrosion. Some Delaware jurisdictions require neutralizers.

Question 9Air conditioning, airflow and accountable installation evidence

What is the recommended method for sizing supply air registers in a residential system?

  1. Use the largest register that fits the opening
  2. Size based on the required CFM for each room and the desired throw distance per Manual T Correct answer.
  3. All rooms get the same size register
  4. Use the smallest register available

Explanation

Supply air registers should be sized based on ACCA Manual T guidelines, considering the required CFM for each room (from the load calculation), desired throw distance to cover the room, acceptable noise level (NC rating), and face velocity. Proper register selection ensures even air distribution and occupant comfort.

Question 10Air conditioning, airflow and accountable installation evidence

What is the correct method for testing a gas furnace heat exchanger for cracks?

  1. Visual inspection only is sufficient
  2. Combination of visual inspection, combustion analysis, and specialized testing (camera inspection, tracer gas, or flame disturbance test) Correct answer.
  3. Listen for unusual sounds
  4. Measure the thermostat temperature

Explanation

A comprehensive heat exchanger inspection includes visual examination for cracks or corrosion, combustion analysis (checking for elevated CO levels), and specialized testing methods such as camera inspection, tracer gas testing, or flame disturbance observation. A cracked heat exchanger can allow carbon monoxide to enter the air stream.

Question 11Air conditioning, airflow and accountable installation evidence

What is the purpose of a blower door test in relation to HVAC system design?

  1. To test the blower motor
  2. To measure the air leakage rate of the building envelope, which affects heating and cooling loads Correct answer.
  3. To test ductwork for leaks
  4. To measure indoor air quality

Explanation

A blower door test measures the air leakage rate of the building envelope by depressurizing or pressurizing the building and measuring the airflow required to maintain a standard pressure difference (typically 50 Pascals). This information is used in Manual J load calculations to determine infiltration loads and assess the building's overall air tightness.

Question 12Air conditioning, airflow and accountable installation evidence

What is the proper method for calculating the total BTU load for equipment selection?

  1. Use the square footage method only
  2. Add the sensible and latent cooling loads from the Manual J calculation, then select equipment per Manual S Correct answer.
  3. Use online calculators without site-specific data
  4. Match the neighbor's system size

Explanation

The intended equipment-selection process uses the actual sensible and latent load and suitable performance data at the relevant conditions. Named design methods do not make floor area or nominal capacity a complete selection. Actual airflow, moisture performance, controls and project requirements still need coordination.

Question 13Air conditioning, airflow and accountable installation evidence

What is the standard approach to sizing a whole-house dehumidifier for a Delaware home?

  1. Install the smallest unit available
  2. Size based on the home's latent load, square footage, number of occupants, and moisture sources Correct answer.
  3. One size fits all homes
  4. Only needed in bathrooms

Explanation

Whole-house dehumidifier sizing considers the home's latent load from the Manual J calculation, total conditioned square footage, number of occupants, moisture sources (cooking, bathing, basement moisture), and the target relative humidity. Delaware's humid summers may require supplemental dehumidification beyond what the AC system provides.

Question 14Air conditioning, airflow and accountable installation evidence

What is the purpose of a commissioning report for a new HVAC system?

  1. To advertise the contractor's services
  2. To document all startup procedures, test results, and performance verification that the system meets design specifications Correct answer.
  3. To submit the final invoice
  4. To register the warranty

Explanation

A commissioning report documents all startup procedures, measurement results (airflows, temperatures, pressures, electrical readings), safety control verification, and overall system performance compared to design specifications. This report serves as a baseline reference for future maintenance and troubleshooting.

Question 15Air conditioning, airflow and accountable installation evidence

What is the primary advantage of a mini-split (ductless) system for Delaware homeowners?

  1. They are always cheaper than ducted systems
  2. Zone-by-zone temperature control without ductwork, ideal for room additions, older homes, and supplemental heating/cooling Correct answer.
  3. They do not require any outdoor equipment
  4. They only work in summer

Explanation

Mini-split (ductless) systems provide zone-by-zone temperature control without the need for ductwork. They are ideal for Delaware homes where adding ductwork is impractical (room additions, older homes, finished basements) and for supplemental heating/cooling in specific areas. Modern mini-splits also provide efficient heating in cold weather.

Question 16Air conditioning, airflow and accountable installation evidence

What is the importance of proper line set sizing in a split-system installation?

  1. Line set size does not affect performance
  2. Incorrect line set sizing causes reduced capacity, oil return problems, and potential compressor damage Correct answer.
  3. Larger lines always improve performance
  4. Any copper tubing will work

Explanation

Proper refrigerant line set sizing is critical for system performance. Undersized suction lines cause excessive pressure drop, reducing capacity and increasing compressor work. Oversized suction lines can impede oil return to the compressor. The liquid line must maintain adequate subcooling. Always follow manufacturer specifications for line sizes.

Question 17Air conditioning, airflow and accountable installation evidence

What is the proper installation method for a condensate pump on an HVAC system?

  1. Any pump will work in any location
  2. Install at or below the evaporator drain pan, verify pump capacity exceeds condensate production, and route discharge to an approved location Correct answer.
  3. Install above the unit for gravity flow
  4. No pump is ever needed

Explanation

A condensate pump should be installed at or below the level of the evaporator drain pan. The pump must have sufficient capacity to handle the maximum condensate flow rate and lift height. The discharge should be routed to an approved location (drain, exterior). A safety overflow switch should be included to shut down the system if the pump fails.

Question 18Operating controls, interlocks, instrumentation, and electrical basics

What is the function of a flame rollout switch on a gas furnace?

  1. To regulate flame height
  2. To shut down the furnace if flames extend outside the combustion chamber, indicating a dangerous condition Correct answer.
  3. To ignite the pilot light
  4. To control the blower motor speed

Explanation

A flame rollout switch is a safety device located near the burner compartment opening. If flames roll out of the combustion chamber (due to a cracked heat exchanger, blocked flue, or inadequate combustion air), the switch opens and shuts down the furnace to prevent fire and carbon monoxide hazards.

Question 19Operating controls, interlocks, instrumentation, and electrical basics

What is the typical defrost cycle method used in modern heat pump systems?

  1. Manual defrost by the homeowner
  2. Demand defrost using temperature and/or time-based sensors to initiate and terminate defrost Correct answer.
  3. Continuous defrost during winter
  4. No defrost is needed in Delaware's climate

Explanation

Modern heat pumps use demand defrost systems that monitor outdoor coil conditions using temperature and/or pressure sensors. Defrost is initiated only when frost accumulation is detected and terminated when the coil is clear. This is more efficient than older time-initiated defrost methods and is important in Delaware's winter climate.

Question 20Operating controls, interlocks, instrumentation, and electrical basics

What is the function of a high-pressure cutout switch on an air conditioning compressor?

  1. To increase refrigerant pressure
  2. To shut down the compressor if discharge pressure exceeds safe operating limits, preventing equipment damage Correct answer.
  3. To control the condenser fan
  4. To monitor refrigerant level

Explanation

A high-pressure cutout switch monitors the compressor discharge (high-side) pressure. If pressure exceeds the safe operating limit (typically 400-600 PSIG depending on refrigerant), the switch opens and shuts down the compressor to prevent damage. Common causes of high pressure include dirty condenser coils, non-condensable gases, or condenser fan failure.

Question 21Operating controls, interlocks, instrumentation, and electrical basics

What is the purpose of balancing dampers in a residential duct system?

  1. To make the system louder
  2. To adjust airflow to individual rooms or zones for even temperature distribution Correct answer.
  3. To block all airflow
  4. To increase system static pressure

Explanation

Balancing dampers are installed in branch ducts to adjust airflow delivery to individual rooms or zones. By partially opening or closing these dampers during system commissioning, the contractor can balance airflow to match each room's heating and cooling load, ensuring even temperature distribution throughout the home.

Question 22Operating controls, interlocks, instrumentation, and electrical basics

What is the function of a low-ambient control on an outdoor condensing unit?

  1. To reduce indoor temperature
  2. To maintain adequate head pressure during cold weather by cycling the condenser fan or using a damper Correct answer.
  3. To speed up the compressor
  4. To increase refrigerant charge

Explanation

A low-ambient control maintains adequate condenser (head) pressure during cold outdoor conditions by cycling the condenser fan on and off or modulating a damper. Without this control, low outdoor temperatures would cause excessively low head pressure, resulting in insufficient refrigerant flow through the metering device and poor system performance.

Question 23Operating controls, interlocks, instrumentation, and electrical basics

What is the function of a solenoid valve in a refrigeration system?

  1. To compress refrigerant
  2. To electrically open or close to control refrigerant flow in response to a control signal Correct answer.
  3. To measure refrigerant pressure
  4. To filter refrigerant

Explanation

A solenoid valve is an electrically operated valve that opens or closes to control refrigerant flow in response to a signal from the control system. Common applications include pump-down solenoid valves (which close on thermostat satisfaction to pump refrigerant into the condenser) and hot gas bypass valves.

Question 24Operating controls, interlocks, instrumentation, and electrical basics

What is a zoning damper motor and how does it work in a residential HVAC system?

  1. It powers the outdoor fan
  2. It opens and closes duct dampers based on thermostat calls from individual zones to control airflow distribution Correct answer.
  3. It controls the compressor speed
  4. It regulates gas flow to the burner

Explanation

A zoning damper motor opens and closes motorized dampers in the ductwork based on temperature calls from zone thermostats. When a zone thermostat calls for heating or cooling, the corresponding damper opens to allow conditioned air into that zone while dampers for satisfied zones may close. A bypass damper or equipment modulation prevents static pressure issues.

Question 25Operating controls, interlocks, instrumentation, and electrical basics

What is the function of a crank case pressure regulator (CPR) on a commercial compressor?

  1. To increase crankcase pressure
  2. To limit suction pressure during startup to prevent motor overload from excessive low-side pressure after a defrost or pulldown Correct answer.
  3. To regulate oil pressure
  4. To control head pressure

Explanation

A crankcase pressure regulator (CPR) limits suction pressure at the compressor inlet during startup, defrost recovery, or initial pulldown. After a defrost cycle, evaporator pressure can be very high. Without a CPR, this high pressure would cause excessive motor amperage, potentially tripping overloads or damaging the compressor motor.

Question 26Refrigerant properties, performance trends, and accountable operation

What is the purpose of a filter drier in a refrigerant system?

  1. To filter the air entering the system
  2. To remove moisture, acids, and particulate contaminants from the refrigerant to protect system components Correct answer.
  3. To dry the outdoor coil
  4. To regulate refrigerant temperature

Explanation

The specified filter-drier can remove relevant moisture and contaminants within its rated material compatibility and finite capacity. It does not repair every contamination source or prove all acid and particles are absent. Correct selection, system condition and actual service instructions remain relevant.

Question 27Refrigerant properties, performance trends, and accountable operation

What is the function of a sight glass in a refrigerant system?

  1. To view the compressor oil level
  2. To observe the liquid refrigerant condition and detect bubbles indicating low charge or flash gas Correct answer.
  3. To view the evaporator coil
  4. To monitor airflow

Explanation

A suitable sight glass permits relevant observation of the local refrigerant condition. Bubbles can result from local flashing or other conditions and are not a unique charge measurement. Compare the actual pressure, temperature, subcooling, load and system instructions before diagnosing or altering the inventory.

Question 28Refrigerant properties, performance trends, and accountable operation

What is the purpose of a pressure-temperature (P-T) chart in HVAC service?

  1. To set thermostat temperatures
  2. To determine the saturation temperature of a refrigerant at a given pressure for diagnostic purposes Correct answer.
  3. To calculate electricity costs
  4. To size ductwork

Explanation

A pressure-temperature (P-T) chart shows the relationship between refrigerant pressure and its saturation (boiling/condensing) temperature. Technicians use P-T charts to determine superheat and subcooling by comparing actual temperatures to the saturation temperature at measured pressures. This is essential for diagnosing system performance.

Question 29Compressor types, lubrication, capacity, and fault reasoning

What is the purpose of a two-stage compressor in a residential heat pump?

  1. It uses two different refrigerants
  2. It operates at high capacity for peak loads and low capacity for mild conditions, improving comfort and efficiency Correct answer.
  3. It has two separate cooling circuits
  4. It automatically switches between heating and cooling

Explanation

A two-stage compressor operates at high capacity when full heating or cooling is needed and at low capacity during mild conditions. This provides better comfort (less temperature swing), improved efficiency (longer run times at lower capacity), better humidity control, and quieter operation compared to single-stage compressors.

Question 30Compressor types, lubrication, capacity, and fault reasoning

What is the importance of proper electrical phasing on three-phase HVAC equipment?

  1. Phasing doesn't matter on three-phase systems
  2. Incorrect phasing causes motors to run backwards, potentially damaging compressors and other equipment Correct answer.
  3. Three-phase equipment has no moving parts
  4. Phasing is only important for lighting

Explanation

Phase sequence can affect the rotation of relevant three-phase motors and equipment. Check actual manufacturer requirements, protections and the competent commissioning process rather than assume every device behaves identically or interchange conductors as an informal test. A correct rotation observation is not complete electrical or equipment acceptance.

Question 31Air conditioning, airflow and accountable installation evidence

What is the purpose of a change order in an HVAC construction project?

  1. To change the project manager
  2. To formally document and agree upon modifications to the original contract scope, price, or timeline Correct answer.
  3. To order new equipment
  4. To change the building inspector

Explanation

A change order is a formal document that modifies the original HVAC contract when changes to the scope of work, price, or project timeline occur. Both the contractor and customer must review and sign the change order. Proper change order documentation prevents disputes and ensures all parties agree to modifications.

Question 32Air conditioning, airflow and accountable installation evidence

What should a Delaware HVAC contractor include in their written estimate?

  1. Only the total price
  2. Detailed scope of work, equipment specifications, labor costs, permit fees, warranty terms, timeline, and payment schedule Correct answer.
  3. Only the equipment brand
  4. A verbal estimate is sufficient

Explanation

A comprehensive written estimate should include the complete scope of work, specific equipment make/model/efficiency, labor costs, material costs, permit fees, warranty terms, project timeline, payment schedule, and any exclusions. This protects both the contractor and customer and prevents disputes about what was included.

Question 33Air conditioning, airflow and accountable installation evidence

What is the proper method for handling customer callbacks on HVAC installations?

  1. Ignore callbacks to save money
  2. Respond promptly, diagnose the issue, perform warranty work as applicable, and document the service for quality improvement Correct answer.
  3. Charge full price for all callbacks
  4. Refer the customer to the manufacturer

Explanation

Professional callback handling includes responding promptly, thoroughly diagnosing the issue, performing warranty repairs at no charge when applicable, documenting the callback for quality improvement tracking, and ensuring customer satisfaction. Callbacks are an opportunity to build trust and identify areas for installation process improvement.

Question 34Air conditioning, airflow and accountable installation evidence

What is the recommended practice for documenting HVAC system modifications or upgrades?

  1. No documentation is needed
  2. Record all changes in writing including equipment specs, as-built drawings updates, and updated maintenance requirements Correct answer.
  3. Verbal communication is sufficient
  4. Only note the date of the work

Explanation

All HVAC system modifications or upgrades should be documented in writing, including updated equipment specifications, as-built drawing revisions, changes to control sequences, updated maintenance requirements, and any code compliance impacts. This documentation is essential for future service, warranty claims, and building records.

Question 35Air conditioning, airflow and accountable installation evidence

What is the primary technical reason for using a reamer on copper tubing after cutting it with a wheel cutter?

  1. To reduce the outside diameter of the tube to fit into smaller fittings
  2. To remove the internal burr created by the cutter to prevent restricted refrigerant flow and turbulence Correct answer.
  3. To polish the outer surface of the copper to ensure a shiny brazing joint
  4. To increase the thickness of the copper wall at the joint location

Explanation

Cutting copper tubing with a wheel cutter creates an internal ridge or burr that reduces the pipe's internal cross-sectional area. Reaming removes this burr, restoring full flow area and preventing refrigerant turbulence, pressure drops, or damage to compressor valves from dislodged metal shavings.

Question 36Refrigerant hazards, emergency response, and regulatory boundaries

If a coworker is experiencing an electric shock in the refrigeration workshop, what is the very first action you should take?

  1. Grab their arm and pull them away from the electrical source
  2. Throw water on the coworker to extinguish any electrical sparks
  3. Immediately switch off or isolate the main power source Correct answer.
  4. Administer cardiopulmonary resuscitation (CPR) immediately before isolating power

Explanation

The first and most critical action is to safely switch off or isolate the main electrical power source to break the current path. Attempting to pull the victim away while they are still in contact with the live source will result in the rescuer also receiving the electric shock. Only after the current is safely disconnected should you assess the victim and administer first aid or CPR.

Question 37Refrigerant hazards, emergency response, and regulatory boundaries

For a specified compatible system and approved competent procedure, which listed pair of methods can help locate a refrigerant leak without using a flame?

  1. Holding a lit match or candle flame near the joint to see if the flame changes color
  2. Applying an approved soap bubble solution or using an electronic leak detector Correct answer.
  3. Submerging the entire joint in a bucket of gasoline to observe chemical reactions
  4. Listening closely by ear for a whistling sound while the system is turned off

Explanation

Using an approved soap bubble solution (which forms bubbles at the leak site) or an electronic leak detector (which senses halogen gases) are the safest and most effective methods to locate leaks. Holding an open flame near joints is extremely dangerous due to the risk of igniting oil or flammable refrigerants, and it can release highly toxic phosgene gas if halocarbon gases are burned.

Question 38Refrigerant hazards, emergency response, and regulatory boundaries

Why is it strictly prohibited to use compressed oxygen or ordinary air to pressurize a refrigeration system for leak testing?

  1. Oxygen is too expensive to use for routine shop leak testing
  2. Oxygen and oil under pressure can cause a violent explosion or fire Correct answer.
  3. Air and oxygen molecules are too large to escape through small leaks
  4. Oxygen will turn the copper piping into brittle brass alloy

Explanation

Pressurizing a refrigeration system with oxygen or compressed air is extremely dangerous because oxygen reacts chemically with the hydrocarbons in refrigeration compressor oil under pressure, creating an explosive mixture that can ignite violently. Dry nitrogen is an inert gas that does not react with oil or support combustion, making it the industry standard for safe pressure testing.

Question 39Refrigerant properties, performance trends, and accountable operation

On a standard HVAC/R service manifold gauge set, what is the function of the blue hose?

  1. Connecting to the high-pressure discharge side of the system
  2. Connecting to the low-pressure suction side of the system Correct answer.
  3. Connecting to the vacuum pump or refrigerant recovery cylinder
  4. Connecting to the high-pressure liquid refrigerant supply tank

Explanation

The blue hose of a standard manifold gauge set connects to the low-pressure (suction) side of the refrigeration system, matching the color-coded blue low-pressure compound gauge. The red hose connects to the high-pressure side, and the center yellow hose is reserved for utility connections like vacuum pumps, recovery units, or refrigerant cylinders.

Question 40Refrigerant properties, performance trends, and accountable operation

On a standard HVAC/R service manifold gauge set, what does the red hose connect to?

  1. The suction service valve or low-pressure port
  2. The discharge service valve or high-pressure port Correct answer.
  3. The vacuum pump inlet connection
  4. The center purging valve

Explanation

The red hose on a manifold gauge set is designated for the high-pressure side of the system, connecting to the discharge service valve, liquid line access fitting, or high-pressure ports. This corresponds to the red high-pressure gauge on the manifold.

Question 41Refrigeration cycle, property references, and energy calculations

What is the term for the heat energy absorbed or released when a substance changes its physical state without changing its temperature?

  1. Sensible heat
  2. Superheat
  3. Latent heat Correct answer.
  4. Subcooled heat

Explanation

Latent heat is the heat energy required to change the state of a substance (e.g., from liquid to gas or solid to liquid) at a constant temperature. During this phase change, the energy is used to break or form molecular bonds rather than increase kinetic energy (temperature). Sensible heat, on the other hand, causes a direct change in temperature.

Question 42Refrigeration cycle, property references, and energy calculations

Which of the following describes 'sensible heat'?

  1. Heat that causes a substance to change from a liquid to a vapor at constant temperature
  2. Heat that causes a change in temperature of a substance that can be measured by a thermometer Correct answer.
  3. The heat required to melt ice into water at 0°C
  4. Heat that changes the chemical composition of a refrigerant gas

Explanation

Sensible heat is the heat energy added to or removed from a substance that results in a measurable change in temperature, without any change in state. This temperature change can be directly read using a thermometer. Latent heat changes the state of the substance without changing its temperature.

Question 43Refrigeration cycle, property references, and energy calculations

In which component of the standard vapor compression cycle does the refrigerant undergo a drop in pressure, causing a portion of it to flash into vapor?

  1. The compressor
  2. The condenser
  3. The expansion device Correct answer.
  4. The evaporator

Explanation

The expansion device (metering device) reduces the pressure of the high-pressure liquid refrigerant coming from the condenser. This sudden pressure drop causes a portion of the liquid to immediately flash into vapor (known as flash gas), which cools the remaining liquid refrigerant to the evaporator temperature.

Question 44Refrigeration cycle, property references, and energy calculations

According to the Second Law of Thermodynamics, how does heat naturally flow between objects?

  1. From a body of lower temperature to a body of higher temperature
  2. From a body of higher temperature to a body of lower temperature Correct answer.
  3. Only through vacuum spaces without any physical contact
  4. Equally in both directions regardless of temperature differences

Explanation

The Second Law of Thermodynamics dictates that heat naturally flows from a region of higher temperature to a region of lower temperature. To reverse this flow (e.g., in a refrigerator where heat is moved from a cold space to a warm room), external mechanical work must be supplied by the compressor.

Question 45Refrigeration cycle, property references, and energy calculations

What is 'subcooling' in a refrigeration system?

  1. The cooling of liquid refrigerant below its saturation condensing temperature at a given pressure Correct answer.
  2. The boiling of liquid refrigerant inside the compressor crankcase
  3. The cooling of vapor refrigerant inside the evaporator coil below its freezing point
  4. The difference between the outdoor air temperature and the indoor air temperature

Explanation

Subcooling is the difference between the saturation temperature of a refrigerant (its condensing point at a given pressure) and the actual temperature of the liquid refrigerant leaving the condenser. Subcooling ensures that the refrigerant entering the expansion valve is 100% liquid, which is necessary for proper valve operation and system efficiency.

Question 46Refrigeration cycle, property references, and energy calculations

What is 'superheat' in a refrigeration system?

  1. The temperature of liquid refrigerant as it leaves the condenser
  2. The temperature of vapor refrigerant above its saturation boiling point at a given pressure Correct answer.
  3. The excess heat generated by a compressor motor during an electrical overload
  4. The heat required to raise water to its boiling point at atmospheric pressure

Explanation

Superheat is the sensible heat added to a refrigerant vapor after it has completely evaporated (turned to gas). It is calculated as the difference between the actual temperature of the vapor leaving the evaporator and the saturation temperature (boiling point) of the refrigerant at that suction pressure. Superheat ensures no liquid refrigerant reaches the compressor.

Question 47Refrigeration cycle, property references, and energy calculations

What happens to the boiling point (saturation temperature) of a refrigerant when its pressure is increased?

  1. The boiling point decreases
  2. The boiling point increases Correct answer.
  3. The boiling point remains exactly the same
  4. The boiling point drops to absolute zero

Explanation

The boiling point of any liquid, including refrigerants, is directly proportional to the pressure exerted upon it. When the pressure increases, the molecules are held closer together, requiring more heat energy (a higher temperature) to break the bonds and boil the liquid into a vapor. This pressure-temperature (P-T) relationship is fundamental to the refrigeration cycle.

Question 48Refrigeration cycle, property references, and energy calculations

What are the three physical modes of heat transfer?

  1. Evaporation, condensation, and expansion
  2. Conduction, convection, and radiation Correct answer.
  3. Compression, subcooling, and superheating
  4. Friction, induction, and combustion

Explanation

Heat is transferred between objects via three modes: conduction (direct molecular contact through solids), convection (movement of fluids or gases), and radiation (electromagnetic waves that transfer heat through space without a medium). These mechanisms are exploited in condensers, evaporators, and system insulation.

Question 49Refrigeration cycle, property references, and energy calculations

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

  1. To absorb heat from the indoor air to boil liquid refrigerant
  2. To reject heat from the high-pressure refrigerant vapor, changing it into a liquid Correct answer.
  3. To pump refrigerant liquid directly to the compressor inlet
  4. To drop the pressure of the refrigerant before it enters the evaporator

Explanation

The condenser is the high-pressure heat exchanger that rejects heat absorbed from the evaporator and the compressor work to the surrounding cooling medium (air or water). As the high-pressure, superheated refrigerant vapor loses heat, it condenses into a high-pressure liquid state.

Question 50Refrigeration cycle, property references, and energy calculations

In a vapor compression refrigeration cycle, what is the primary function of the evaporator?

  1. To reject heat from the system to the outdoor air
  2. To absorb heat from the space being cooled, causing the low-pressure liquid refrigerant to boil into vapor Correct answer.
  3. To compress low-pressure vapor into a high-pressure liquid
  4. To filter oil and moisture out of the refrigerant before the expansion valve

Explanation

The evaporator is the low-pressure heat exchanger where heat from the refrigerated space or air is transferred to the cold, low-pressure liquid refrigerant. This heat absorption causes the refrigerant to boil at a constant low saturation temperature, changing state into a vapor and cooling the space.