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HVAC Excellence Refrigeration study materials
HVAC Excellence Refrigeration study resources

HVAC Excellence Refrigeration practice questions

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Question 1Refrigeration Fundamentals

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

  1. Remove moisture and non-condensables from the refrigerant charge
  2. Absorb heat from the conditioned space to boil the refrigerant
  3. Reject heat from the high-pressure refrigerant vapor so it condenses to liquid Correct answer.
  4. Reduce refrigerant pressure between the receiver and the evaporator

Explanation

The condenser is the heat-rejection coil: desuperheated vapor gives up sensible heat, then latent heat, until it becomes a saturated or subcooled liquid at condensing pressure. Heat removed from the space in the evaporator plus compressor work is discharged here. Pressure reduction is the metering device's job, not the condenser's.

Question 2Refrigeration Fundamentals

Which component creates the pressure difference that drives refrigerant flow around a vapor-compression circuit?

  1. The liquid line filter-drier
  2. The evaporator fan
  3. The accumulator
  4. The compressor Correct answer.

Explanation

The compressor raises refrigerant vapor from evaporating pressure to condensing pressure, and that pressure difference moves refrigerant through the metering device and the rest of the circuit. Without the compressor the system would equalize and no sustained refrigeration would occur. The other listed parts have no pumping function.

Question 3Refrigeration Fundamentals

What is the state of the refrigerant as it leaves the evaporator of a properly charged direct-expansion system?

  1. A two-phase liquid-vapor mixture at high pressure
  2. Subcooled high-pressure liquid
  3. Saturated high-pressure vapor
  4. Superheated low-pressure vapor Correct answer.

Explanation

Refrigerant boils in the evaporator and is fully vaporized before the outlet, with a few degrees of superheat added to protect the compressor from liquid slugging. The refrigerant is at low (evaporating) pressure, not high pressure. Subcooled liquid is found at the condenser outlet.

Question 4Refrigeration Fundamentals

What does the saturated suction temperature (SST) on a low-temperature refrigeration system represent?

  1. The ambient temperature surrounding the condenser
  2. The boiling temperature of the refrigerant at suction pressure Correct answer.
  3. The temperature of the air leaving the evaporator coil
  4. The temperature of the refrigerant at the compressor discharge

Explanation

Saturated suction temperature is the saturation (boiling) temperature corresponding to the measured suction pressure. It is a pressure-derived value, not a measured pipe temperature. Comparing it with actual suction line temperature gives superheat.

Question 5Refrigeration Fundamentals

A technician measures a suction line temperature of 45°F and a suction pressure corresponding to 30°F saturation. What is the superheat?

  1. 45°F
  2. 15°F Correct answer.
  3. 75°F
  4. 30°F

Explanation

Superheat is the difference between the actual suction line temperature and the saturated suction temperature at the same pressure. Here 45°F minus 30°F equals 15°F. Superheat is always a temperature difference, never a sum of the two readings.

Question 6Refrigeration Fundamentals

Which pressure-enthalpy diagram segment represents the heat absorbed by the evaporator?

  1. The short vertical drop through the metering device
  2. The horizontal line from compressor discharge to the condenser outlet
  3. The horizontal line from the expansion device outlet to the evaporator outlet Correct answer.
  4. The near-vertical line rising from the suction to the discharge pressure

Explanation

On a pressure-enthalpy diagram, the evaporator is drawn as a horizontal segment at evaporating pressure from the metering-device outlet to the evaporator outlet, and its length equals the refrigerating effect in Btu per pound. Compression is the near-vertical line rising to discharge pressure. Condensing is the horizontal segment at high pressure.

Question 7Refrigeration Fundamentals

What is the effect of raising the condensing pressure while suction pressure stays the same?

  1. The refrigerating effect per pound increases significantly
  2. The compression ratio increases and compressor power rises Correct answer.
  3. The evaporator superheat automatically decreases
  4. The compression ratio decreases and power consumption falls

Explanation

Compression ratio is discharge absolute pressure divided by suction absolute pressure, so a higher condensing pressure raises the ratio. Higher ratio means more work per pound of refrigerant and higher discharge temperatures. Refrigerating effect per pound is set mainly by the evaporator and changes little.

Question 8Refrigeration Fundamentals

A refrigerant cylinder is at 70°F and its pressure gauge reads the saturation pressure for 70°F. What does this indicate about the cylinder contents?

  1. The cylinder holds saturated liquid and vapor in equilibrium Correct answer.
  2. The cylinder contains only non-condensable gas
  3. The cylinder is overfilled with liquid
  4. The cylinder is empty and the gauge is faulty

Explanation

In a closed cylinder containing both liquid and vapor, the pressure equals the saturation pressure at the cylinder temperature. At 70°F the gauge should read the table value for 70°F. Pressure above that value suggests non-condensables or an overfill, while pressure far below suggests an empty or nearly empty cylinder.

Question 9Refrigeration Fundamentals

Which statement correctly describes the difference between a zeotropic blend and an azeotropic refrigerant?

  1. An azeotrope has a large temperature glide, while a zeotrope behaves as a single-component fluid
  2. Zeotropic blends cannot be used in direct-expansion evaporators
  3. Azeotropic refrigerants must always be charged as liquid only
  4. A zeotropic blend has a measurable temperature glide during phase change, while an azeotrope boils at essentially one temperature Correct answer.

Explanation

Zeotropic blends change composition between liquid and vapor phases, so they boil and condense over a temperature range called glide. Azeotropes behave like a single substance and change phase at essentially constant temperature. Glide affects evaporator design, charging method, and superheat interpretation.

Question 10Refrigeration Fundamentals

Why is a small amount of superheat required at the evaporator outlet of a direct-expansion system?

  1. To allow the condenser to subcool more effectively
  2. To ensure no liquid droplets reach the compressor Correct answer.
  3. To raise the evaporating pressure above the condensing pressure
  4. To increase the temperature glide of the refrigerant

Explanation

Superheat provides a safety margin that confirms all liquid has boiled off before the refrigerant returns to the compressor. Liquid entering a reciprocating compressor can wash away lubricant and cause mechanical damage. Superheat has no effect on establishing the pressure difference.

Question 11Refrigeration Fundamentals

A system has a suction pressure of 20 psig and a discharge pressure of 180 psig. Using atmospheric pressure of 15 psi, what is the approximate compression ratio?

  1. 11.6
  2. 9.0
  3. 4.3
  4. 5.3 Correct answer.

Explanation

Convert to absolute pressures: suction 20 plus 15 equals 35 psia, discharge 180 plus 15 equals 195 psia. Divide 195 by 35 to get about 5.6, closest to 5.3 among the choices when rounded from the stated values. Compression ratio must always use absolute pressure, never gauge pressure.

Question 12Refrigeration Fundamentals

What happens to the boiling point of a refrigerant as the evaporating pressure is lowered?

  1. The boiling temperature stays the same
  2. The boiling temperature increases
  3. The boiling temperature becomes independent of pressure
  4. The boiling temperature decreases Correct answer.

Explanation

Saturation temperature follows saturation pressure: lower pressure means a lower boiling temperature for the same refrigerant. That is why lowering suction pressure produces a colder evaporator and greater temperature difference with the load. Pressure and saturation temperature always move together.

Question 13Refrigeration Fundamentals

Which condition indicates that a refrigeration system is undercharged with refrigerant?

  1. High superheat and low subcooling Correct answer.
  2. Normal superheat with elevated suction pressure
  3. High subcooling and high discharge pressure
  4. Low superheat and a flooded evaporator

Explanation

A shortage of refrigerant starves the evaporator, producing high superheat, and leaves little liquid in the condenser, producing low subcooling. Suction and discharge pressures also tend to run low. High subcooling with high head pressure points instead to overcharge or non-condensables.

Question 14Refrigeration Fundamentals

What is the purpose of subcooling the liquid refrigerant leaving the condenser?

  1. To raise the compression ratio
  2. To increase the temperature glide of the blend
  3. To ensure the liquid line contains only liquid refrigerant with no flash gas Correct answer.
  4. To increase the superheat at the evaporator outlet

Explanation

Subcooling removes additional sensible heat so the liquid entering the metering device is below saturation temperature. This margin prevents flash gas in the liquid line and increases the refrigerating effect per pound. It does not directly control evaporator superheat or compression ratio.

Question 15Refrigeration Fundamentals

Which of the following best describes the function of the metering device in a refrigeration circuit?

  1. It regulates refrigerant flow and reduces pressure from the liquid line to the evaporator Correct answer.
  2. It rejects heat from the refrigerant to the outdoor air
  3. It separates oil from the discharge gas
  4. It compresses vapor from evaporating to condensing pressure

Explanation

The metering device throttles high-pressure liquid to the lower evaporating pressure and controls the flow rate to match load. The pressure drop causes part of the liquid to flash, cooling the remaining liquid to the evaporating temperature. Compression and heat rejection occur elsewhere.

Question 16Refrigeration Fundamentals

A technician reads a liquid line temperature of 95°F and a liquid pressure corresponding to 110°F saturation. What is the subcooling?

  1. 95°F
  2. 15°F Correct answer.
  3. 110°F
  4. 205°F

Explanation

Subcooling is the saturated condensing temperature minus the actual liquid line temperature. Here 110°F minus 95°F equals 15°F. The liquid line should be cooler than the saturation temperature when subcooling is present.

Question 17Refrigeration Fundamentals

Which of these is a non-condensable gas that commonly contaminates a refrigeration system and raises head pressure?

  1. Refrigerant vapor
  2. Air Correct answer.
  3. Carbon dioxide
  4. Nitrogen

Explanation

Air that enters during service raises discharge pressure and subcooling because it cannot condense at normal condensing temperatures and occupies condenser volume. The result is high head pressure with bubbly or reduced liquid. Nitrogen is normally used deliberately for pressure testing and must be removed before charging.

Question 18Refrigeration Fundamentals

What does a lower-than-normal suction pressure with normal superheat most likely suggest?

  1. A condenser fan failure
  2. An overcharged system
  3. A restricted or underfed evaporator, such as a clogged screen or low load Correct answer.
  4. Excessive subcooling in the liquid line

Explanation

Low suction pressure with normal superheat suggests the evaporator is receiving too little refrigerant or too little heat load, as with a restriction, a dirty screen, or low airflow. An overcharge or condenser problem would raise head pressure and typically alter subcooling. Isolating whether superheat is high or normal narrows the cause.

Question 19Refrigeration Fundamentals

Which refrigerant safety classification indicates the lowest flammability and lowest toxicity under ASHRAE 34?

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

Explanation

ASHRAE 34 uses a letter for toxicity (A lower, B higher) and a number for flammability (1 lowest through 3 highest). A1 therefore denotes the lowest toxicity and lowest flammability. B classifications indicate higher toxicity regardless of the flammability number.

Question 20Refrigeration Fundamentals

Why must refrigerant be recovered rather than vented when servicing a system?

  1. Venting lowers the saturation temperature of the remaining charge
  2. Venting reduces system efficiency on the next startup
  3. Refrigerant harms the ozone layer or contributes to global warming, and venting is regulated Correct answer.
  4. Venting causes oil to remain in the compressor

Explanation

Refrigerants are regulated because CFCs and HCFCs deplete stratospheric ozone and most refrigerants are potent greenhouse gases. Recovery, recycling, and reclamation keep them out of the atmosphere. Venting is prohibited by environmental regulations for these reasons.

Question 21Refrigeration Fundamentals

A reciprocating compressor has a measured compression ratio well above the manufacturer's recommended limit. What is the most likely consequence if it continues to operate?

  1. Reduced volumetric efficiency and high discharge temperatures that can degrade oil and valves Correct answer.
  2. Increased evaporator superheat with no effect on the compressor
  3. Automatic increase in condenser subcooling
  4. Lower discharge temperatures and longer compressor life

Explanation

Excessive compression ratio increases re-expansion losses in the clearance volume, lowering volumetric efficiency, and raises discharge temperature. Sustained high discharge temperatures can carbonize oil, damage valves, and shorten compressor life. Correcting high head pressure or low suction pressure restores the ratio.

Question 22Refrigeration Fundamentals

What is the primary reason a liquid-line filter-drier is installed in a refrigeration system?

  1. To increase the pressure of the liquid before the metering device
  2. To remove moisture and particulate contaminants that could form acids or block the metering device Correct answer.
  3. To add superheat to the suction line
  4. To store excess refrigerant during low-load operation

Explanation

The filter-drier traps solid particles and absorbs moisture that could combine with refrigerant to form acids or freeze at the metering device. Keeping the circuit clean protects the compressor and prevents restrictions. It does not pump, heat, or store refrigerant.

Question 23Refrigeration Fundamentals

In a capillary-tube system, what primarily determines the amount of refrigerant flow to the evaporator?

  1. A solenoid valve cycling with the thermostat
  2. The fixed restriction of the tube and the pressure difference across it Correct answer.
  3. The compressor unloading mechanism
  4. A sensing bulb modulating a needle valve

Explanation

A capillary tube is a fixed restriction, so flow depends on the pressure difference between the condenser and evaporator and on the tube's bore and length. There is no modulating element. Charge amount is therefore critical, since the system relies on the tube and charge to balance.

Question 24Refrigeration Fundamentals

What is the effect of a restricted suction line on system operation?

  1. Lower suction pressure at the compressor with higher superheat Correct answer.
  2. Higher suction pressure at the compressor with lower superheat
  3. Higher discharge pressure with increased subcooling
  4. No measurable change in operating pressures

Explanation

A restriction between the evaporator and compressor causes a pressure drop, so the compressor sees lower suction pressure. The reduced refrigerant mass flow starves the evaporator and raises superheat. The restriction also lowers capacity and may cause the compressor to overheat.

Question 25Refrigeration Fundamentals

Which of the following best explains why an accumulator is used on some low-temperature systems?

  1. It prevents liquid refrigerant from reaching the compressor during off-cycle migration or flooding Correct answer.
  2. It replaces the metering device during low-load conditions
  3. It removes non-condensable gases from the condenser
  4. It raises the evaporating pressure to improve capacity

Explanation

An accumulator is installed in the suction line to trap liquid refrigerant and allow it to boil off before returning to the compressor. This protects against slugging during off-cycle migration or sudden load changes. It does not change evaporating pressure or replace the metering device.

Question 26Refrigeration Fundamentals

In a refrigeration system operating on the vapor-compression cycle, which component rejects heat from the refrigerant to the surrounding air or water?

  1. The metering device
  2. The condenser Correct answer.
  3. The accumulator
  4. The evaporator

Explanation

The condenser is the heat-rejection coil in the vapor-compression cycle; desuperheating, condensation, and subcooling all occur there as the refrigerant gives up heat to the ambient air or water. The evaporator absorbs heat instead, and the metering device and accumulator do not perform heat rejection.

Question 27Refrigeration Fundamentals

Which refrigerant state exists in the suction line of a properly operating direct-expansion refrigeration system?

  1. Low-pressure saturated liquid
  2. High-pressure saturated vapor
  3. Low-pressure superheated vapor Correct answer.
  4. High-pressure subcooled liquid

Explanation

The suction line carries refrigerant from the evaporator outlet back to the compressor, so it must be low-pressure vapor with a few degrees of superheat to protect the compressor from liquid slugging. Liquid refrigerant in the suction line would indicate flooding or an overcharge.

Question 28Refrigeration Fundamentals

A technician measures a compressor suction pressure of 40 psig and a discharge pressure of 200 psig. Using an atmospheric pressure of 15 psi, what is the compression ratio?

  1. 5.4 to 1
  2. 5.0 to 1
  3. 3.9 to 1 Correct answer.
  4. 4.6 to 1

Explanation

Compression ratio is absolute discharge pressure divided by absolute suction pressure. Adding 15 psi to each gauge reading gives 215 psia and 55 psia, and 215 divided by 55 equals approximately 3.9 to 1.

Question 29Refrigeration Fundamentals

A refrigerant blend has a temperature glide of 8°F. What does this glide value indicate about the blend?

  1. It cannot be used in a direct-expansion evaporator
  2. It has a saturation pressure equal to zero at room temperature
  3. It boils and condenses over a range of temperatures at a given pressure Correct answer.
  4. It changes from liquid to vapor at a single fixed temperature

Explanation

Temperature glide is the difference between the bubble point and dew point of a zeotropic blend at a given pressure, so the refrigerant changes phase over a temperature range rather than at one fixed temperature. This affects charging method and evaporator design but does not prevent the blend from being used.

Question 30Refrigeration Fundamentals

A technician observes frost forming on the suction line right at the outlet of the evaporator while the space temperature is well above setpoint. Which condition most likely explains this?

  1. The thermostat is set too low for the ambient conditions
  2. The condenser fan is cycling too frequently
  3. The evaporator is starved of refrigerant because of an undercharge Correct answer.
  4. The system is overcharged and liquid is backing up into the suction line

Explanation

Frost at the evaporator outlet with a warm box points to low refrigerant flow, so the small amount of refrigerant present boils off early and the remaining coil surface and suction line drop below freezing. An undercharge starves the coil and produces this pattern.

Question 31Refrigeration Fundamentals

What is the purpose of the oil separator installed on the discharge line of some refrigeration compressors?

  1. To remove entrained oil from the hot gas and return it to the crankcase Correct answer.
  2. To filter acid and particulate matter from the refrigerant
  3. To remove moisture from the refrigerant before it reaches the condenser
  4. To reduce the discharge pressure before the gas enters the condenser

Explanation

An oil separator is placed in the discharge line to knock out oil carried with the hot gas and route it back to the compressor crankcase, which keeps oil from accumulating in the evaporator and reducing heat transfer. Moisture and acid removal are the job of filter-driers, not separators.

Question 32Refrigeration Fundamentals

Which statement correctly describes the role of the compressor in the vapor-compression cycle?

  1. It controls the flow of liquid refrigerant into the evaporator
  2. It removes heat from the refrigerant as it passes through the coil
  3. It raises the refrigerant pressure so the gas can be condensed at ambient temperature Correct answer.
  4. It lowers the refrigerant pressure so the liquid can boil in the evaporator

Explanation

The compressor takes low-pressure vapor from the evaporator and compresses it to a higher pressure whose saturation temperature is above the ambient, allowing the condenser to reject heat. Lowering pressure for evaporation is the metering device's job.

Question 33Refrigeration Fundamentals

A technician finds that the evaporator is freezing solid while the suction pressure is lower than normal and the superheat is high. Which component is the most likely cause?

  1. A thermostat set to a colder-than-normal setpoint
  2. A condenser fan motor running at full speed
  3. A restricted or clogged liquid-line filter-drier Correct answer.
  4. An oversized evaporator coil

Explanation

A restricted filter-drier reduces liquid flow to the metering device, which starves the evaporator and produces low suction pressure with high superheat and eventual coil icing. Normal condenser airflow and setpoint changes would not create this combination of readings.

Question 34Refrigeration Fundamentals

What is the effect on a refrigeration system when the evaporator airflow is reduced while the compressor continues to run?

  1. Discharge pressure falls and the superheat decreases
  2. The refrigerant charge decreases because less heat is absorbed
  3. Suction pressure drops and the coil temperature falls, promoting frost formation Correct answer.
  4. Suction pressure rises and the coil temperature rises

Explanation

Reduced airflow means less heat is transferred to the refrigerant, so the refrigerant boils less and suction pressure falls while the coil gets colder, which promotes frost. The charge does not change; only the heat load and resulting pressures and temperatures change.

Question 35Refrigeration Fundamentals

Which of these best explains why a thermostatic expansion valve is equipped with an external equalizer line?

  1. To compensate for the pressure drop across the evaporator when the valve is used on a distributor-fed coil Correct answer.
  2. To bypass the valve during defrost
  3. To allow the valve to open fully during the off cycle
  4. To sense the temperature of the liquid line leaving the condenser

Explanation

The external equalizer applies the actual evaporator outlet pressure to the underside of the diaphragm so the valve responds to superheat at the coil outlet rather than at the valve inlet. This matters when a distributor or long evaporator creates a significant pressure drop.

Question 36Refrigeration Fundamentals

Which factor most directly determines the saturation temperature of refrigerant inside the evaporator?

  1. The size of the compressor crankcase
  2. The length of the liquid line
  3. The temperature of the air leaving the condenser
  4. The pressure maintained in the evaporator Correct answer.

Explanation

For a given refrigerant, saturation temperature is fixed by saturation pressure, so the evaporator pressure set by the metering device and compressor determines the boiling temperature. Other system components influence that pressure indirectly but do not determine saturation temperature directly.

Question 37Refrigeration Fundamentals

A system using R-404A shows a suction pressure corresponding to 10°F saturation and an evaporator outlet temperature of 22°F. What is the superheat?

  1. 12°F Correct answer.
  2. 22°F
  3. 10°F
  4. 32°F

Explanation

Superheat is the difference between the actual vapor temperature and the saturation temperature at the same pressure. Subtracting 10°F from 22°F gives 12°F of superheat.

Question 38Refrigeration Fundamentals

A technician is evacuating a system and observes that the vacuum holds steady when the pump is isolated. What does this result indicate?

  1. The system still contains a significant amount of moisture
  2. The system is free of leaks and moisture has been removed to an acceptable level Correct answer.
  3. The system has a leak that is admitting air
  4. The vacuum pump is undersized for the system volume

Explanation

A standing vacuum that does not rise after the pump is valved off indicates that no air or moisture is entering and that the system is tight. A rising vacuum would suggest a leak or continued outgassing from moisture.

Question 39Refrigeration Fundamentals

Which statement best describes the relationship between the boiling point of a refrigerant and the pressure acting on it?

  1. Increasing the pressure raises the boiling point of the refrigerant Correct answer.
  2. Changing the pressure has no effect on the boiling point
  3. Increasing the pressure lowers the boiling point of the refrigerant
  4. The boiling point depends only on the refrigerant volume

Explanation

Saturation temperature rises with saturation pressure for every refrigerant, which is why the compressor must raise pressure before the condenser can reject heat. Lowering pressure has the opposite effect and is what allows the evaporator to boil refrigerant at a low temperature.

Question 40Refrigeration Fundamentals

A technician is diagnosing a system that cools poorly, with high suction pressure, low superheat, and a sweating suction line at the compressor. Which condition best fits these readings?

  1. The system is low on refrigerant charge
  2. The evaporator fan is running faster than design
  3. The expansion valve is overfeeding refrigerant to the evaporator Correct answer.
  4. The condenser is rejecting too much heat

Explanation

High suction pressure with low superheat and a sweating suction line indicates that excess liquid refrigerant is reaching the compressor, which is characteristic of an overfeeding expansion valve. An undercharge would show low suction pressure and high superheat instead.

Question 41Refrigerants and Lubricants

Which refrigerant is classified as an A1 refrigerant under ASHRAE Standard 34?

  1. R-410A Correct answer.
  2. R-290 (propane)
  3. R-717 (ammonia)
  4. R-1234yf

Explanation

ASHRAE 34 classifies R-410A as A1, meaning low toxicity and no flame propagation at standard test conditions. A1 is the safest classification combination used in the standard.

Question 42Refrigerants and Lubricants

A refrigerant cylinder is stamped with a DOT 4BA specification. What does this indicate?

  1. It is a refillable cylinder rated for a specific service pressure Correct answer.
  2. It is a cylinder used solely for nitrogen pressurization
  3. It is approved only for recovery of CFCs
  4. It is a disposable one-way cylinder

Explanation

DOT 4BA cylinders are refillable and rated for the marked service pressure, and they must be requalified periodically. Disposable cylinders carry different DOT markings and may not be refilled.

Question 43Refrigerants and Lubricants

Which lubricant is most commonly charged with HFC refrigerants such as R-134a in automotive and commercial systems?

  1. Mineral oil
  2. Polyolester (POE) Correct answer.
  3. Naphthenic mineral oil
  4. Alkylbenzene

Explanation

HFC refrigerants are not miscible with mineral oil, so polyolester lubricants are used because they carry oil through the system with the refrigerant. POE is hygroscopic and must be kept sealed.

Question 44Refrigerants and Lubricants

What color is the recovery cylinder required to be for refrigerant recovery per common industry practice?

  1. Gray with a yellow top
  2. Green with a yellow band
  3. Yellow with a gray body Correct answer.
  4. Red with a white stripe

Explanation

Recovery cylinders are commonly yellow with a gray body, a convention used to distinguish them from virgin refrigerant cylinders. Always verify the cylinder label rather than relying on color alone.

Question 45Refrigerants and Lubricants

A technician is recovering refrigerant from a system and the recovery cylinder becomes full. What is the correct action?

  1. Vent the remaining refrigerant to atmosphere
  2. Transfer the refrigerant into a disposable cylinder
  3. Stop recovery and switch to an empty recovery cylinder Correct answer.
  4. Continue recovery until the system is empty

Explanation

Recovery cylinders must never be filled beyond the marked capacity, typically 80 percent by weight, so the correct action is to switch to an empty cylinder. Venting refrigerant is prohibited, and disposable cylinders may not be refilled.

Question 46Refrigerants and Lubricants

Which statement correctly describes the difference between a refrigerant's boiling point and its dew point in a zeotropic blend?

  1. The boiling point is always higher than the dew point
  2. The dew point is the temperature at which the blend begins to condense Correct answer.
  3. The dew point applies only to azeotropes
  4. They are identical for all blends

Explanation

In a zeotropic blend, the components condense and evaporate over a temperature range, so the dew point marks the start of condensation and the bubble point marks the end. The difference between them is the temperature glide.

Question 47Refrigerants and Lubricants

What is the primary reason HFC refrigerants are being phased down under the AIM Act?

  1. They have high global warming potential Correct answer.
  2. They are toxic to humans
  3. They are flammable at room temperature
  4. They deplete stratospheric ozone

Explanation

HFCs do not contain chlorine and have negligible ozone depletion potential, but they are potent greenhouse gases with high GWP values. The AIM Act targets their production and consumption to reduce climate impact.

Question 48Refrigerants and Lubricants

Which refrigerant is classified as a natural refrigerant and has a GWP of approximately 1?

  1. R-744 (carbon dioxide) Correct answer.
  2. R-404A
  3. R-134a
  4. R-22

Explanation

R-744 is carbon dioxide, a naturally occurring refrigerant with a GWP reference value of 1. It is increasingly used in transcritical commercial refrigeration systems.

Question 49Refrigerants and Lubricants

A technician must add POE oil to an R-410A system. Why should the oil container be kept sealed except when pouring?

  1. POE loses its lubricity when exposed to light
  2. POE becomes flammable when exposed to air
  3. POE evaporates rapidly at room temperature
  4. POE absorbs moisture readily from the air Correct answer.

Explanation

POE is hygroscopic and absorbs moisture from ambient air, which can lead to acid formation and system contamination. Containers should be sealed immediately after use and oil should not be left open.

Question 50Refrigerants and Lubricants

Which oil type is most appropriate for a system using R-22 with a mineral oil charge?

  1. Polyalkylene glycol
  2. Polyolester
  3. Mineral oil Correct answer.
  4. Polyvinyl ether

Explanation

R-22 is an HCFC and is miscible with mineral oil, which is the traditional lubricant for these systems. HFCs require synthetic lubricants such as POE or PVE.