I85PREP
⌘ K
RETA CARO study materials
RETA CARO study resources

RETA CARO practice questions

One question at a time. Build your RETA CARO understanding.

First 50 of 200 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 1Industrial Refrigeration I

In a basic vapor-compression refrigeration cycle, which component raises the pressure of the refrigerant from evaporating pressure to condensing pressure?

  1. The compressor Correct answer.
  2. The evaporator
  3. The expansion valve
  4. The receiver

Explanation

The compressor is the only component that adds work to the refrigerant vapor and lifts it from the low-side evaporating pressure to the high-side condensing pressure. The other components either absorb or reject heat or throttle flow.

Question 2Industrial Refrigeration I

Which refrigerant state exists at the outlet of a properly operating evaporator?

  1. Saturated liquid
  2. Subcooled liquid
  3. Two-phase mixture
  4. Superheated vapor Correct answer.

Explanation

A properly fed evaporator completely boils the refrigerant and adds a small amount of superheat so no liquid droplets reach the compressor. Subcooled liquid and two-phase mixture describe other points in the cycle.

Question 3Industrial Refrigeration I

What is the primary purpose of the condenser in an industrial refrigeration system?

  1. To separate oil from the discharge gas
  2. To remove moisture from the refrigerant
  3. To meter refrigerant into the evaporator
  4. To reject heat from the refrigerant to the ambient medium Correct answer.

Explanation

The condenser transfers heat from the hot high-pressure discharge gas to a cooling medium such as air or water, condensing the refrigerant to liquid. Moisture removal and oil separation are handled by other devices.

Question 4Industrial Refrigeration I

In a direct-expansion (DX) evaporator, refrigerant is fed by which device?

  1. A hand expansion valve only
  2. A thermostatic expansion valve Correct answer.
  3. A liquid pump
  4. A surge drum

Explanation

A DX evaporator uses a thermostatic expansion valve to meter refrigerant and maintain superheat at the coil outlet. Pumped and flooded systems use different feed arrangements.

Question 5Industrial Refrigeration I

What does the term 'superheat' describe in refrigeration?

  1. The temperature difference across the condenser
  2. The temperature of refrigerant above its saturation temperature at a given pressure Correct answer.
  3. The pressure drop across the expansion valve
  4. The amount of liquid refrigerant in the receiver

Explanation

Superheat is the number of degrees a vapor is above its saturation temperature at the existing pressure. It is used to verify proper expansion valve operation and compressor protection.

Question 6Industrial Refrigeration I

Which of the following is a common industrial refrigerant that is a natural substance with zero ozone depletion potential?

  1. R-134a
  2. Ammonia (R-717) Correct answer.
  3. R-410A
  4. R-22

Explanation

Ammonia (R-717) is a natural refrigerant with an ozone depletion potential of zero and is widely used in industrial refrigeration. The other listed refrigerants are synthetic halocarbons.

Question 7Industrial Refrigeration I

What is the function of the oil separator in an industrial refrigeration system?

  1. To cool the compressor discharge gas
  2. To regulate refrigerant flow to the evaporator
  3. To remove oil entrained in the discharge gas and return it to the compressor Correct answer.
  4. To filter moisture from the liquid line

Explanation

Oil separator removes oil carried with the hot discharge gas so it does not accumulate in the evaporator or condenser, and returns it to the compressor crankcase. It does not cool gas or filter refrigerant.

Question 8Industrial Refrigeration I

A pressure-enthalpy diagram shows the refrigeration effect of a cycle as which quantity?

  1. The enthalpy difference across the condenser
  2. The enthalpy at the expansion valve inlet
  3. The enthalpy difference across the evaporator Correct answer.
  4. The enthalpy rise across the compressor

Explanation

Refrigeration effect is the enthalpy gain of the refrigerant as it passes through the evaporator, equal to the enthalpy at the evaporator outlet minus the enthalpy at the expansion valve outlet. Compressor work is the enthalpy rise across the compressor.

Question 9Industrial Refrigeration I

An evaporator operates at a saturation temperature of -20°F. The refrigerant leaving the coil is at -14°F. What is the superheat?

  1. 20°F
  2. 14°F
  3. 6°F Correct answer.
  4. 34°F

Explanation

Superheat equals the actual vapor temperature minus the saturation temperature at the same pressure: -14°F minus -20°F equals 6°F. The other values come from adding or using the wrong reference.

Question 10Industrial Refrigeration I

A condenser receives discharge gas and discharges liquid at a condensing temperature of 95°F. The liquid line temperature measured at the condenser outlet is 85°F. What is the subcooling?

  1. 180°F
  2. 85°F
  3. 95°F
  4. 10°F Correct answer.

Explanation

Subcooling is the saturation condensing temperature minus the actual liquid temperature: 95°F minus 85°F equals 10°F. Subcooling confirms the condenser is fully condensing the refrigerant.

Question 11Industrial Refrigeration I

In a flooded evaporator system, what maintains the liquid refrigerant level in the evaporator or surge drum?

  1. A liquid level control such as a float or electronic level sensor Correct answer.
  2. A thermostatic expansion valve responding to superheat
  3. A hand expansion valve set once at commissioning
  4. The compressor suction valve

Explanation

Flooded systems keep the evaporator and surge drum partially filled with liquid, and a level control device modulates refrigerant feed to hold that level. Superheat-based expansion valves are used in DX systems instead.

Question 12Industrial Refrigeration I

What is the effect of a fouled condenser on system performance?

  1. Refrigerant charge decreases automatically
  2. Evaporating temperature falls and superheat decreases
  3. Suction pressure rises and capacity increases
  4. Discharge pressure rises and compressor power increases Correct answer.

Explanation

Fouling reduces heat transfer, so the condenser cannot reject heat as effectively and discharge pressure climbs. Higher discharge pressure raises compression ratio and compressor power while reducing capacity.

Question 13Industrial Refrigeration I

Which statement correctly describes the difference between a reciprocating and a screw compressor in industrial refrigeration?

  1. Reciprocating compressors have no suction or discharge valves
  2. Reciprocating compressors are positive displacement with pistons, while screw compressors use intermeshing rotors Correct answer.
  3. Screw compressors rely on centrifugal force to raise pressure
  4. Reciprocating compressors are centrifugal, while screw compressors are positive displacement

Explanation

Reciprocating compressors are positive-displacement machines using pistons and valves, while screw compressors are also positive displacement but use intermeshing rotors to trap and compress gas. Neither type is centrifugal.

Question 14Industrial Refrigeration I

Why is liquid slugging dangerous to a reciprocating compressor?

  1. It can cause hydraulic damage to valves and connecting rods because liquid is incompressible Correct answer.
  2. It increases oil viscosity in the crankcase
  3. It improves volumetric efficiency
  4. It reduces discharge pressure below suction pressure

Explanation

Liquid refrigerant entering the compressor cannot be compressed and can bend valves, break connecting rods, or damage the crankshaft. Superheat at the compressor suction is maintained to prevent this condition.

Question 15Industrial Refrigeration I

In a pumped liquid recirculation system, what does the term 'recirculation ratio' describe?

  1. The ratio of condenser water flow to refrigerant flow
  2. The ratio of suction pressure to discharge pressure
  3. The mass of liquid refrigerant pumped per mass of refrigerant evaporated Correct answer.
  4. The fraction of compressor capacity used for subcooling

Explanation

Recirculation ratio is the mass of liquid fed to the evaporator divided by the mass actually vaporized. Higher ratios improve wetting and heat transfer in flooded coils.

Question 16Industrial Refrigeration I

A refrigeration system has a suction pressure of 20 psig (saturation -10°F) and a discharge pressure of 150 psig (saturation 95°F). What is the compression ratio (absolute pressures)?

  1. About 2.5
  2. About 1.3
  3. About 4.6 Correct answer.
  4. About 7.5

Explanation

Compression ratio is absolute discharge pressure divided by absolute suction pressure: (150+14.7)/(20+14.7) = 164.7/34.7 ≈ 4.6. Using gauge pressures without adding atmospheric pressure is a common error.

Question 17Industrial Refrigeration I

What is the purpose of a liquid receiver in a refrigeration system?

  1. To store liquid refrigerant and accommodate charge variations Correct answer.
  2. To superheat the suction gas
  3. To separate oil from the discharge gas
  4. To increase evaporator pressure

Explanation

The receiver holds liquid refrigerant leaving the condenser and provides storage as the system charge and load vary. It does not superheat gas, separate oil, or raise evaporator pressure.

Question 18Industrial Refrigeration I

Which condition indicates that an expansion valve is overfeeding an evaporator?

  1. High subcooling at the condenser
  2. High superheat and starved coil
  3. Low superheat and possible liquid floodback Correct answer.
  4. Low discharge pressure

Explanation

An overfeeding valve admits too much refrigerant, so the coil floods and superheat drops, risking liquid floodback to the compressor. High superheat indicates underfeeding instead.

Question 19Industrial Refrigeration I

What is the primary hazard associated with ammonia refrigerant in industrial systems?

  1. It is heavier than air and collects in low areas
  2. It depletes the ozone layer rapidly
  3. It is toxic and irritating to eyes and respiratory tract at low concentrations Correct answer.
  4. It is highly flammable at room temperature

Explanation

Ammonia is toxic and irritating even at low concentrations, so systems require detection, ventilation, and personal protective equipment. It is not flammable at normal conditions, has zero ODP, and is lighter than air.

Question 20Industrial Refrigeration I

A technician measures an evaporator approach of 12°F when the design approach is 6°F. What is the most likely cause?

  1. A closed liquid line solenoid valve
  2. Reduced heat transfer from fouling or poor airflow Correct answer.
  3. Excess refrigerant charge in the receiver
  4. Too much compressor oil in the crankcase

Explanation

A larger-than-design approach means the evaporator is not transferring heat efficiently, often due to fouled surfaces or reduced airflow. Charge and oil level do not directly set approach.

Question 21Industrial Refrigeration I

Why is a purge unit used on a low-pressure ammonia system?

  1. To remove noncondensable gases that raise condensing pressure Correct answer.
  2. To add refrigerant charge to the receiver
  3. To remove oil from the evaporator
  4. To increase suction superheat

Explanation

Air and other noncondensables accumulate in the condenser and raise head pressure, so a purge unit removes them. Purge units do not add charge, remove oil, or adjust superheat.

Question 22Industrial Refrigeration I

In a two-stage compression system with a flash intercooler, what is the main benefit?

  1. It raises the evaporating temperature above the load temperature
  2. It reduces the compression ratio per stage and improves efficiency Correct answer.
  3. It removes the need for an expansion valve
  4. It eliminates the need for a condenser

Explanation

Splitting compression into two stages reduces the ratio each stage must handle and a flash intercooler cools gas between stages, improving efficiency and discharge temperature. The condenser and expansion valves are still required.

Question 23Industrial Refrigeration I

A system with R-717 operates with an evaporating temperature of -30°F and a condensing temperature of 90°F. Why might a single-stage compressor be a poor choice compared with two-stage?

  1. The evaporator would freeze
  2. Single-stage compressors cannot use ammonia
  3. The expansion valve cannot handle the pressure differential
  4. The high compression ratio causes excessive discharge temperature and low volumetric efficiency Correct answer.

Explanation

A large ratio between -30°F and 90°F conditions produces high discharge temperatures and reduced volumetric efficiency, so two-stage compression is preferred. Ammonia works in single-stage systems, and expansion valves handle large differentials.

Question 24Industrial Refrigeration I

What happens to compressor capacity and power as the condensing pressure rises while the evaporating pressure stays constant?

  1. Capacity decreases and power increases Correct answer.
  2. Both capacity and power increase
  3. Both capacity and power decrease
  4. Capacity increases and power decreases

Explanation

A higher condensing pressure increases the compression ratio, so the compressor moves less mass per stroke and requires more work per unit mass, reducing capacity while raising power. The other combinations contradict this relationship.

Question 25Industrial Refrigeration I

A receiver is sized for an industrial plant. Which factor most directly determines the required receiver volume?

  1. The condenser water flow rate
  2. The total system refrigerant charge and the ability to pump down Correct answer.
  3. The number of evaporator fans
  4. The compressor oil charge

Explanation

Receiver volume must hold the system charge, including the liquid that can be pumped down from evaporators and lines during service. Oil charge, water flow, and fan count do not determine receiver volume.

Question 26Industrial Refrigeration I

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

  1. To raise refrigerant vapor from a lower pressure to a higher pressure so heat can be rejected Correct answer.
  2. To meter refrigerant flow into the evaporator
  3. To store liquid refrigerant until it is needed
  4. To remove heat from the refrigerated space directly

Explanation

The compressor is a vapor pump; it raises the pressure and temperature of the vapor so the condenser can reject heat to a warmer medium. Heat removal from the space occurs in the evaporator, not the compressor.

Question 27Industrial Refrigeration I

Which component in a vapor-compression system is responsible for rejecting heat from the refrigerant to the ambient air or water?

  1. Expansion valve
  2. Evaporator
  3. Condenser Correct answer.
  4. Suction accumulator

Explanation

The condenser removes the heat of compression and latent heat from the hot discharge gas, condensing it to liquid. The evaporator absorbs heat, and the expansion valve and accumulator serve other functions.

Question 28Industrial Refrigeration I

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

  1. The temperature of the refrigerant above its saturation temperature at that pressure Correct answer.
  2. The difference between condensing and evaporating temperature
  3. The amount of liquid refrigerant leaving the coil
  4. The pressure drop across the evaporator coil

Explanation

Superheat is the number of degrees a vapor is above its saturation temperature at the measured pressure. It confirms that all liquid has boiled off before the vapor reaches the compressor.

Question 29Industrial Refrigeration I

Why is a thermostatic expansion valve equipped with an external equalizer line on a large evaporator?

  1. To keep the valve body warm enough to prevent frosting
  2. To compensate for the pressure drop through the evaporator when setting superheat Correct answer.
  3. To provide a bypass path for hot gas during defrost
  4. To vent refrigerant to the atmosphere during overpressure

Explanation

An external equalizer applies the actual evaporator outlet pressure to the underside of the diaphragm, so the coil pressure drop does not falsely affect superheat control. Internally equalized valves work only where the drop is small.

Question 30Industrial Refrigeration I

Which of the following best describes a 'direct expansion' (DX) evaporator?

  1. The coil is submerged in a tank of secondary coolant
  2. Refrigerant is fed by an expansion valve and boils off as it travels through the coil Correct answer.
  3. The evaporator operates only with flooded ammonia
  4. Liquid refrigerant is pumped over the coil from a surge drum

Explanation

In a DX coil the expansion valve meters just enough liquid so it evaporates as it moves through the circuit, leaving superheated vapor at the outlet. Flooded and pumped systems use a different liquid-feed arrangement.

Question 31Industrial Refrigeration I

What is the function of the king valve on a liquid receiver?

  1. It acts as a safety relief device
  2. It regulates the condensing pressure automatically
  3. It meters liquid into the evaporator
  4. It isolates the receiver from the rest of the system for service Correct answer.

Explanation

The king valve is the main receiver outlet valve that can be front-seated to isolate the receiver from the system. This allows pump-down or service work on the receiver.

Question 32Industrial Refrigeration I

What is the purpose of a suction-line accumulator in a refrigeration system?

  1. To cool the discharge gas before the condenser
  2. To store high-pressure liquid for the evaporator
  3. To prevent liquid refrigerant from reaching the compressor Correct answer.
  4. To boost suction pressure before the compressor

Explanation

An accumulator traps any liquid carryover and allows it to boil off before vapor continues to the compressor. This protects the compressor from slugging.

Question 33Industrial Refrigeration I

Which safety device protects an industrial refrigeration compressor from dangerously high discharge pressure?

  1. High-pressure cutout Correct answer.
  2. Oil level switch
  3. Low-pressure cutout
  4. Suction filter drier

Explanation

A high-pressure cutout stops the compressor when discharge pressure exceeds a set limit, preventing relief valve discharge or equipment damage. Low-pressure cutouts protect against low suction, not high discharge.

Question 34Industrial Refrigeration I

A technician reads a suction pressure corresponding to 5°F saturation and a suction line temperature of 15°F. What is the superheat?

  1. 5°F
  2. 10°F Correct answer.
  3. 15°F
  4. 20°F

Explanation

Superheat equals the measured suction temperature minus the saturation temperature at the same pressure. Here 15°F − 5°F = 10°F.

Question 35Industrial Refrigeration I

An ammonia system has an evaporating temperature of −20°F and a condensing temperature of 100°F. What is the temperature lift?

  1. 100°F
  2. 20°F
  3. 120°F Correct answer.
  4. 80°F

Explanation

Temperature lift is the difference between condensing and evaporating temperatures: 100°F − (−20°F) = 120°F. Lift drives the compression ratio and power required.

Question 36Industrial Refrigeration I

What is the main reason a centrifugal (rotary) liquid pump is used in a recirculated liquid overfeed system?

  1. To raise the refrigerant from evaporating pressure to condensing pressure
  2. To transfer liquid from the high-pressure receiver to the condenser
  3. To compress vapor before it enters the high-stage compressor
  4. To circulate liquid refrigerant from the low-pressure receiver through the evaporators Correct answer.

Explanation

A refrigerant pump moves liquid from the low-pressure receiver to the evaporators, supplying more liquid than boils off. The excess returns to the receiver, improving coil wetting and heat transfer.

Question 37Industrial Refrigeration I

A condenser is operating with a condensing temperature of 105°F while the design value is 95°F. Which condition most likely explains this?

  1. The evaporator is starved of refrigerant
  2. The condenser has excessive air or noncondensable gas in it Correct answer.
  3. The expansion valve is set with too much superheat
  4. The compressor is short-cycling on the low-pressure control

Explanation

Noncondensable gases such as air collect in the condenser and raise the effective condensing pressure and temperature for a given heat load. Purging restores normal performance.

Question 38Industrial Refrigeration I

In a liquid overfeed system, what does a recirculation ratio of 3:1 mean?

  1. The condenser rejects three times the evaporator load
  2. Three evaporators share one expansion valve
  3. The compressor runs three times per hour
  4. Three pounds of liquid are supplied for each pound vaporized in the coil Correct answer.

Explanation

The recirculation ratio compares the mass of liquid fed to the evaporator with the mass that actually evaporates. A 3:1 ratio means three parts are pumped for each part boiled off.

Question 39Industrial Refrigeration I

Why is a liquid-to-suction heat exchanger sometimes installed between the liquid line and suction line?

  1. To remove moisture from the refrigerant
  2. To reduce the compressor discharge temperature
  3. To increase the evaporating pressure
  4. To subcool the liquid and superheat the suction vapor Correct answer.

Explanation

The heat exchanger transfers heat from the warm liquid to the colder suction vapor, subcooling the liquid and superheating the vapor. This can improve evaporator performance but raises discharge temperature.

Question 40Industrial Refrigeration I

Which statement best explains why a screw compressor often uses an oil injection system?

  1. Oil seals the rotor clearances and absorbs heat of compression Correct answer.
  2. Oil replaces the need for a condenser
  3. Oil is the primary refrigerant in the system
  4. Oil increases the compression ratio

Explanation

Injected oil seals the gaps between rotors and casing, lubricates bearings, and removes heat of compression. This allows higher single-stage pressure ratios and quieter operation.

Question 41Industrial Refrigeration I

What is the purpose of a discharge oil separator in an ammonia plant?

  1. To remove noncondensable gases from the system
  2. To cool the discharge gas before it reaches the condenser
  3. To separate liquid ammonia from vapor after the condenser
  4. To remove oil from the hot discharge gas so it does not accumulate in the evaporator Correct answer.

Explanation

The oil separator captures oil entrained in the discharge gas and returns it to the compressor crankcase. Oil in the evaporator reduces heat transfer and can cause foaming.

Question 42Industrial Refrigeration I

A system uses a thermosyphon oil cooler. What does this device rely on to cool the compressor oil?

  1. Refrigerant liquid that evaporates while cooling the oil Correct answer.
  2. Chilled water circulated through the oil cooler
  3. A fan blowing air across the oil cooler
  4. A separate mechanical refrigeration unit

Explanation

A thermosyphon cooler uses refrigerant liquid from the high side that evaporates as it absorbs heat from the oil. The vapor returns to the condenser or receiver, and the cycle repeats without a pump.

Question 43Industrial Refrigeration I

A plant uses a two-stage system with an intercooler. What is the main purpose of the intercooler?

  1. To increase the temperature of the vapor before the high stage
  2. To store liquid refrigerant for the evaporator
  3. To remove oil from the suction line
  4. To cool the vapor between compression stages and reduce the high-stage discharge temperature Correct answer.

Explanation

Intercooling removes heat from the vapor between stages, which lowers high-stage discharge temperature and improves efficiency. It also reduces the work the high stage must do.

Question 44Industrial Refrigeration I

A compressor has a displacement of 250 cfm and a volumetric efficiency of 80%. What is the actual capacity in cfm?

  1. 200 cfm Correct answer.
  2. 250 cfm
  3. 312.5 cfm
  4. 50 cfm

Explanation

Actual capacity equals displacement times volumetric efficiency: 250 × 0.80 = 200 cfm. Volumetric efficiency accounts for re-expansion, leakage, and heating losses.

Question 45Industrial Refrigeration I

Why is a hot gas defrost used in some industrial evaporators?

  1. To add moisture to the coil surface
  2. To melt frost from the coil using compressed discharge vapor Correct answer.
  3. To reduce the suction pressure during defrost
  4. To lower the coil temperature below freezing

Explanation

Hot gas defrost routes warm discharge vapor through the coil to melt frost. This restores heat transfer and airflow without relying on electric heaters.

Question 46Industrial Refrigeration I

A technician finds the evaporator is starved of liquid, with high superheat and low suction pressure. Which component is the most likely cause?

  1. The condenser is fouled
  2. The receiver is overfilled
  3. The expansion valve is underfeeding Correct answer.
  4. The compressor is oversized

Explanation

High superheat with low suction pressure indicates the expansion valve is not supplying enough liquid to fill the coil. Checking the valve, its screen, and the liquid supply is the next step.

Question 47Industrial Refrigeration I

In a cascade refrigeration system, what separates the two refrigerant circuits?

  1. A cascade condenser that acts as the evaporator for the high stage Correct answer.
  2. A common compressor
  3. A single expansion valve shared by both circuits
  4. One receiver serving both circuits

Explanation

The cascade condenser transfers heat from the low-stage discharge to the high-stage evaporating refrigerant. The two circuits have separate compressors, valves, and refrigerant charges.

Question 48Industrial Refrigeration I

A plant's evaporators are frosting heavily on the coil and airflow is reduced. Which condition best explains the reduced system capacity?

  1. Frost increases the recirculation ratio
  2. Frost insulates the coil, lowering heat transfer and raising the effective approach Correct answer.
  3. Frost lowers the condensing pressure
  4. Frost improves coil heat transfer by increasing surface area

Explanation

A frost layer acts as insulation between the air and the coil, reducing heat transfer and airflow. Capacity falls and the coil-to-air approach increases until defrost restores performance.

Question 49Industrial Refrigeration I

Why does an industrial refrigeration system use a low-pressure receiver with a liquid level control in a pumped system?

  1. To store high-pressure liquid for the condenser
  2. To separate vapor from liquid and maintain a liquid seal for the pump Correct answer.
  3. To remove oil from the suction line
  4. To regulate the compressor discharge pressure

Explanation

The low-pressure receiver separates returned liquid and vapor and holds a liquid level that keeps the refrigerant pump from cavitating. Level control maintains that seal under varying loads.

Question 50Industrial Refrigeration I

A compressor shows a rising discharge temperature and a falling oil pressure while running. Which combination of causes is most consistent with these readings?

  1. A defrost cycle in progress on one evaporator
  2. A low evaporator load with a clean condenser
  3. An overcharged receiver and a closed king valve
  4. Oil pump wear reducing lubrication and a high compression ratio Correct answer.

Explanation

Falling oil pressure suggests the oil pump or its clearances are worn, reducing lubrication and heat removal. A high compression ratio raises discharge temperature, and together these indicate the compressor needs service.