I85PREP
⌘ K
NATE CR Service study materials
NATE CR Service study resources

NATE CR Service practice questions

One question at a time. Build your NATE CR Service 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 1Commercial Refrigeration

A walk-in cooler holds product at 35°F with a 10°F evaporator TD. A technician measures a 20°F TD after a compressor replacement. What is the most likely immediate effect on the space?

  1. Space temperature rises and compressor run time increases Correct answer.
  2. Space temperature falls and the compressor cycles more often
  3. Evaporator superheat drops to zero and the TXV hunts
  4. Condensing pressure falls and the head pressure control opens

Explanation

A larger evaporator-to-space temperature difference means the coil is running colder relative to the box, which happens when suction pressure is too low or the coil is starved. Capacity at the desired box temperature drops, so the compressor runs longer and the space warms. Superheat and head pressure are separate control loops and are not the direct consequence described.

Question 2Commercial Refrigeration

Which refrigerant is classified A1 by ASHRAE Standard 34?

  1. R-404A Correct answer.
  2. R-290 (propane)
  3. R-1234yf
  4. R-717 (ammonia)

Explanation

ASHRAE 34 assigns a letter for toxicity (A = lower toxicity, B = higher) and a number for flammability (1 = no flame propagation, 2L/2/3 = increasingly flammable). R-404A is a nonflammable, lower-toxicity HFC blend and is rated A1. Ammonia is B2L, R-1234yf is A2L, and propane is A3.

Question 3Commercial Refrigeration

A commercial reach-in freezer uses an off-cycle defrost and the coil ices heavily between cycles. Which condition best explains this?

  1. Defrost termination sensor is open
  2. Evaporator fan motors are drawing high current
  3. Door gaskets are leaking humid air into the cabinet Correct answer.
  4. Suction line accumulator is flooded

Explanation

Off-cycle defrost relies on the coil warming above freezing while the compressor is off. A continuous infiltration of moist room air through failed gaskets adds latent load that freezes faster than the off time can melt it. Defrost termination, fan current, and accumulator flooding affect other symptoms.

Question 4Commercial Refrigeration

What is the primary purpose of a liquid line filter-drier in a commercial refrigeration system?

  1. Store excess refrigerant charge during pump-down
  2. Remove moisture and particulate contamination from the refrigerant Correct answer.
  3. Maintain constant head pressure during low ambient
  4. Reduce suction superheat at the evaporator outlet

Explanation

The filter-drier combines a desiccant to adsorb moisture with a screen or bonded core to trap debris, protecting the TXV and compressor from acid and solids. It does not control superheat, head pressure, or charge storage.

Question 5Commercial Refrigeration

A technician reads 12°F superheat at the evaporator outlet of a medium-temperature display case with a TXV. The design superheat is 8°F. Which adjustment is appropriate?

  1. Turn the TXV adjusting stem counterclockwise to reduce superheat
  2. Add refrigerant until superheat drops
  3. Replace the TXV power head
  4. Turn the TXV adjusting stem clockwise to reduce superheat Correct answer.

Explanation

On most TXV designs, turning the adjusting stem clockwise increases spring force, which closes the valve slightly and lowers superheat. Counterclockwise raises superheat. Charge level and power head replacement are not indicated by a modest 4°F deviation.

Question 6Commercial Refrigeration

Which statement best describes the function of a crankcase pressure regulator on a commercial refrigeration system?

  1. It maintains a minimum condensing pressure in cold weather
  2. It regulates liquid subcooling at the receiver outlet
  3. It bypasses hot gas to the evaporator during defrost
  4. It limits suction pressure at the compressor during startup and pull-down Correct answer.

Explanation

A crankcase pressure regulator is set to limit the suction pressure the compressor sees, protecting the motor from overload during high-load pull-down or after defrost. Head pressure control, hot gas defrost, and subcooling are separate functions.

Question 7Commercial Refrigeration

A parallel rack system serving a supermarket has one compressor with a failed unloader. Which symptom is most likely?

  1. Condensing pressure rises above the fan cycling set point
  2. The liquid line sight glass shows bubbles
  3. The rack cannot unload capacity and suction pressure drops below set point during low load Correct answer.
  4. The defrost timer advances too quickly

Explanation

Unloaders reduce compressor capacity by holding suction valves open, allowing the rack to match low load without cycling off. A failed unloader keeps full capacity engaged, so suction pressure falls below the control band during light load. The other symptoms belong to condenser, charge, or timer faults.

Question 8Commercial Refrigeration

What is the correct leak detection method for a system containing R-717 (ammonia)?

  1. Electronic refrigerant detector rated for ammonia or sulfur stick Correct answer.
  2. Halide torch
  3. Soap bubbles only
  4. Ultraviolet dye with black light

Explanation

Ammonia is toxic and mildly flammable, so an electronic detector rated for ammonia or the traditional sulfur stick (which forms a white smoke) is appropriate. A halide torch is for halogenated refrigerants and would produce dangerous fumes with ammonia, and dyes are not used in ammonia systems.

Question 9Commercial Refrigeration

A walk-in freezer has a subcooler and the liquid line sight glass shows continuous bubbles at the TXV inlet. Subcooling measured at the condenser outlet is 12°F. What is the most likely cause?

  1. Failed evaporator fan motor
  2. Restriction in the suction line
  3. Undercharge of refrigerant
  4. Flash gas from excessive pressure drop in the liquid line Correct answer.

Explanation

Adequate subcooling at the condenser outlet rules out a simple undercharge. Bubbles at the TXV inlet with good subcooling point to pressure drop along the liquid line (long run, undersized line, or a restricted filter-drier) causing the liquid to flash before the valve. Suction line restriction and fan failure do not create liquid line bubbles.

Question 10Commercial Refrigeration

Which component prevents liquid refrigerant from returning to the compressor during low-load operation in a commercial system?

  1. Evaporator pressure regulator
  2. Liquid line solenoid
  3. Head pressure control valve
  4. Suction line accumulator Correct answer.

Explanation

The suction line accumulator traps liquid slugs and allows them to boil off before vapor reaches the compressor. A liquid line solenoid controls flow to the evaporator, a head pressure valve controls condensing pressure, and an EPR controls evaporator pressure.

Question 11Commercial Refrigeration

A medium-temperature walk-in has a suction pressure that is 10 psig below design and normal superheat. What is the most likely cause?

  1. A dirty condenser
  2. A misadjusted TXV with low superheat
  3. A failed evaporator fan motor Correct answer.
  4. A restricted liquid line filter-drier

Explanation

A failed evaporator fan reduces airflow and heat load on the coil, which can lower suction pressure. A normally regulating TXV can maintain normal superheat as the load falls, making fan failure the best listed diagnosis. A liquid-line restriction severe enough to starve the evaporator generally raises superheat.

Question 12Commercial Refrigeration

What is the purpose of a liquid line solenoid valve in a pump-down cycle?

  1. It stops liquid flow to the evaporator so the compressor can pump the low side down Correct answer.
  2. It bypasses hot gas during defrost
  3. It modulates liquid flow to maintain superheat
  4. It maintains minimum condensing pressure

Explanation

During pump-down the liquid line solenoid closes, stopping refrigerant feed, and the compressor runs until the low-side pressure switch trips. This prevents liquid migration to the compressor during off cycles. Superheat modulation is the TXV's job, and hot gas and head pressure control are separate circuits.

Question 13Commercial Refrigeration

A technician is brazing a new liquid line into a system containing R-448A. Which practice is required?

  1. Purge with oxygen to prevent oxidation
  2. Braise without purging to save time
  3. Flow dry nitrogen through the line while brazing Correct answer.
  4. Use only lead-tin solder

Explanation

Dry nitrogen purge displaces oxygen inside the tubing, preventing formation of copper oxide scale that can migrate and plug the filter-drier or TXV. Oxygen purge creates a fire hazard, no purge leaves scale, and lead-tin solder is not used for refrigeration-grade joints.

Question 14Commercial Refrigeration

A commercial ice machine produces cloudy, soft cubes and the harvest cycle is slow. Which condition is most likely?

  1. Low water level or restricted water inlet Correct answer.
  2. Excess refrigerant charge
  3. Failed bin thermostat
  4. High ambient temperature at the condenser

Explanation

Cloudy, soft ice and slow harvest indicate insufficient water flow through the evaporator, often from a restricted inlet screen or low water level. Charge, ambient, and bin thermostat faults produce different symptoms such as long freeze cycles or premature shutoff.

Question 15Commercial Refrigeration

Which refrigerant has the lowest GWP among the following commonly used in commercial refrigeration?

  1. R-507A
  2. R-744 (CO2) Correct answer.
  3. R-448A
  4. R-404A

Explanation

R-744 (carbon dioxide) has a GWP of 1 by definition. R-404A and R-507A are high-GWP HFC blends, and R-448A is a lower-GWP blend but still far above CO2. This is why CO2 is favored in cascade and transcritical systems.

Question 16Commercial Refrigeration

A technician is troubleshooting a system with a suction-line filter and finds a 15 psi pressure drop across it. What does this indicate?

  1. The filter is restricted and should be replaced Correct answer.
  2. The filter is clean and operating normally
  3. The TXV is stuck open
  4. The system is overcharged

Explanation

Suction line filters should show minimal pressure drop, typically a few psi at most. A 15 psi drop indicates a plugged element that restricts flow and reduces capacity, so replacement is required. Overcharge and a stuck TXV would not produce pressure drop across the suction filter.

Question 17Commercial Refrigeration

What is the function of an evaporator pressure regulator (EPR) in a supermarket rack system?

  1. It limits compressor suction pressure on startup
  2. It controls liquid subcooling
  3. It maintains a minimum evaporator pressure to keep product from freezing Correct answer.
  4. It maintains a minimum condensing pressure

Explanation

An EPR holds the evaporator at a set pressure corresponding to a safe coil temperature, protecting medium-temperature product from freezing when rack suction is pulled low by other loads. Crankcase regulators limit compressor suction, and head pressure and subcooling are separate controls.

Question 18Commercial Refrigeration

A technician is evacuating a refrigeration system and the micron gauge stalls at 1,500 microns and rises slowly when the pump is isolated. What does this indicate?

  1. The vacuum pump is oversized
  2. The micron gauge is reading in inches of mercury
  3. The system is fully dehydrated
  4. Moisture or a leak causing outgassing in the system Correct answer.

Explanation

A slow rise after isolation indicates either a leak admitting air or moisture continuing to vaporize under vacuum. A properly dehydrated, leak-free system holds below 500 microns. Pump sizing and gauge units do not explain the rise.

Question 19Commercial Refrigeration

Which safety hazard is unique to a transcritical CO2 refrigeration system compared with an HFC system?

  1. Very high operating pressures requiring rated components and relief devices Correct answer.
  2. Toxicity requiring supplied-air respirators
  3. Flammability of the refrigerant
  4. Ozone depletion potential

Explanation

Transcritical CO2 operates at pressures well above 1,000 psig on the high side, so components, tubing, and relief devices must be rated for those pressures. CO2 is nonflammable, has low toxicity, and has zero ODP, so the other options do not apply.

Question 20Commercial Refrigeration

A reach-in refrigerator has a thermostatic expansion valve and the evaporator is frosting unevenly, with frost only on the first passes. What is the most likely cause?

  1. The evaporator fan is running too fast
  2. The TXV is starved due to a restriction or low charge Correct answer.
  3. The defrost timer is set too long
  4. The condenser is oversized

Explanation

Frost forming only on the inlet passes indicates that liquid refrigerant is boiling off early, leaving later circuits starved. This is typical of a restricted TXV, a plugged inlet screen, or low charge. Fan speed, oversized condenser, and long defrost do not produce this pattern.

Question 21Commercial Refrigeration

What is the primary reason for using a receiver in a commercial refrigeration system?

  1. To reduce compressor discharge temperature
  2. To remove moisture from the refrigerant
  3. To control evaporator superheat
  4. To store liquid refrigerant and accommodate varying load and charge conditions Correct answer.

Explanation

The receiver provides a reservoir of liquid so the TXV always has a solid liquid column and the system can tolerate changes in charge distribution as loads vary. Moisture removal is the filter-drier's job, superheat is the TXV's, and discharge temperature is managed by other means.

Question 22Commercial Refrigeration

A technician measures 0°F superheat at the evaporator outlet of a walk-in cooler and frost on the suction line back to the compressor. What is the most likely cause?

  1. Condenser fan is failed
  2. TXV is stuck closed
  3. System is undercharged
  4. TXV is stuck open or oversized Correct answer.

Explanation

Zero superheat with frost on the suction line means liquid refrigerant is reaching the compressor, indicating the TXV is flooding the coil, either stuck open or oversized. A stuck-closed valve or undercharge would produce high superheat, and a failed condenser fan raises head pressure.

Question 23Commercial Refrigeration

Which practice is required when recovering refrigerant from a commercial system under EPA Section 608 rules for appliances containing 5 or more pounds of refrigerant?

  1. Recover only the liquid portion and vent the vapor
  2. Release refrigerant if the system is being scrapped
  3. Use certified recovery equipment and evacuate to the required vacuum level Correct answer.
  4. Vent the refrigerant to atmosphere if it is a blend

Explanation

Section 608 requires certified technicians using certified recovery equipment to evacuate appliances to specified vacuum levels before opening the system or disposing of it. Venting refrigerant, whether liquid or vapor, is prohibited for these appliances.

Question 24Commercial Refrigeration

A commercial freezer with an air-cooled condenser shows high head pressure, high subcooling, and normal suction pressure. Which cause is most likely?

  1. Noncondensable gas in the system Correct answer.
  2. Failed evaporator fan
  3. TXV stuck open
  4. Low refrigerant charge

Explanation

Noncondensable gas such as air accumulates in the condenser, raising head pressure and subcooling while leaving suction largely unaffected. Low charge lowers subcooling, a failed evaporator fan raises superheat, and a stuck-open TXV raises suction pressure.

Question 25Commercial Refrigeration

What is the correct procedure for checking the charge in a system with a receiver and sight glass?

  1. Weigh in charge only after the compressor trips
  2. Check superheat at the compressor inlet
  3. Clear the sight glass and verify subcooling at the condenser outlet Correct answer.
  4. Add refrigerant until suction pressure reaches design

Explanation

With a receiver, the sight glass should be clear of bubbles at stable conditions, and subcooling at the condenser outlet confirms a solid liquid seal. Suction pressure alone is not a charge indicator, and superheat at the compressor inlet is not used for charging.

Question 26Commercial Refrigeration

A commercial walk-in cooler uses a thermostatic expansion valve. Which condition at the evaporator outlet indicates the valve is feeding correctly?

  1. Superheat within the manufacturer's specified range at the sensing bulb location Correct answer.
  2. Zero superheat with frost forming on the suction line
  3. Subcooling measured at the evaporator outlet
  4. Suction pressure equal to the head pressure

Explanation

The TXV modulates refrigerant flow to maintain a small, controlled superheat at the evaporator outlet, typically 6 to 10°F for a medium-temperature cooler. Measuring superheat at the bulb location confirms the valve is neither starving nor flooding the coil.

Question 27Commercial Refrigeration

A technician is preparing to braze a new copper line into an operating R-404A system. Which precaution protects the system interior?

  1. Wet the fittings with refrigerant oil before heating
  2. Cap both ends of the tubing before applying heat
  3. Increase acetylene pressure to shorten heat time
  4. Purge dry nitrogen through the tubing while brazing Correct answer.

Explanation

A slow nitrogen purge displaces oxygen inside the tubing so copper oxide scale does not form during brazing. Scale that flakes off later can clog the TXV screen, filter drier, and compressor.

Question 28Commercial Refrigeration

A reach-in freezer with a forced-air evaporator has heavy frost only on the lower third of the coil. What is the most probable cause?

  1. The distributor nozzle is oversized for the circuit Correct answer.
  2. The coil has a partial oil-logging condition
  3. The defrost termination sensor is failing
  4. The evaporator fan motor is running backward

Explanation

An oversized distributor nozzle sends excess refrigerant to the coil circuits, so the lower passes flood and frost heavily while upper circuits starve. The uneven pattern points to refrigerant distribution rather than defrost control.

Question 29Commercial Refrigeration

A supermarket rack uses an EPR on a medium-temperature circuit. What happens if the EPR is set too high relative to design?

  1. The compressor cycles on the low-pressure control more often
  2. The case evaporator runs warmer and product temperature rises Correct answer.
  3. The liquid line solenoid fails to open
  4. The condenser subcooling increases sharply

Explanation

The EPR holds a minimum evaporating pressure to keep the coil above freezing. Setting it too high raises the evaporating temperature, reducing the temperature difference between refrigerant and air, so the case cannot pull down to design.

Question 30Commercial Refrigeration

A technician finds a 20 psi pressure drop across a suction-line filter shell on a running rack. What is the correct interpretation?

  1. The TXV is stuck wide open
  2. The system is overcharged with refrigerant
  3. The filter element is restricted and should be replaced Correct answer.
  4. The filter is operating normally and needs no action

Explanation

A suction filter is normally near zero pressure drop when clean; a 20 psi drop indicates a plugged element that is starving the compressor and reducing capacity. The element should be replaced and the cause of debris investigated.

Question 31Commercial Refrigeration

A pump-down cycle on a walk-in freezer does not fully pump out before the compressor stops. Which component is the most likely cause?

  1. The condenser fan cycling control is misadjusted
  2. The liquid line solenoid is leaking through when de-energized Correct answer.
  3. The evaporator fan delay is set too short
  4. The defrost timer is set too long

Explanation

Pump-down relies on the liquid line solenoid closing tightly so the compressor can evacuate the low side. A solenoid that leaks by allows refrigerant to keep feeding the evaporator, so the low-pressure control never reaches its setpoint.

Question 32Commercial Refrigeration

A technician measures 8°F subcooling at the condenser outlet of an R-134a medium-temperature system. What does this value primarily indicate?

  1. The amount of vapor superheated above evaporating temperature
  2. The compressor's volumetric efficiency
  3. The amount of liquid refrigerant cooled below condensing temperature Correct answer.
  4. The pressure drop across the evaporator coil

Explanation

Subcooling is the difference between the condensing temperature (from the high-side gauge) and the liquid line temperature. It confirms that liquid has been cooled below saturation, which correlates with proper charge and condenser performance.

Question 33Commercial Refrigeration

A commercial ice machine's harvest cycle is slow and cubes are cloudy and soft. Which condition should be checked first?

  1. Excess refrigerant charge in the receiver
  2. Insufficient water flow or scale buildup on the evaporator Correct answer.
  3. A miswired bin thermostat
  4. A failed condenser fan motor

Explanation

Cloudy, soft cubes and slow harvest indicate the water side is not delivering enough mineral-free water or the evaporator plate is scaled. Poor water flow or scale insulates the plate, slowing ice formation and release.

Question 34Commercial Refrigeration

A technician must leak-check a system containing R-744 (CO2) in the subcritical portion of a booster system. Which method is appropriate?

  1. Open flame halide torch at each joint
  2. Litmus paper at the condenser inlet
  3. Sulfur candle at the compressor suction
  4. Electronic leak detector rated for CO2 with pressure held and soap bubbles at joints Correct answer.

Explanation

CO2 leaks are best found with an electronic detector rated for the refrigerant and confirmed with soap bubbles at suspected joints. CO2 is heavier than air and can accumulate in low areas, so ventilation is also required.

Question 35Commercial Refrigeration

A commercial freezer condenser has high head pressure, high subcooling, and normal suction pressure. Which condition best fits these readings?

  1. A refrigerant undercharge
  2. A failed evaporator fan motor
  3. Non-condensable gas or a restricted condenser airflow Correct answer.
  4. A stuck-open TXV

Explanation

High head pressure with high subcooling points to reduced condenser heat rejection, such as dirty coils, restricted airflow, or non-condensable gas. Normal suction pressure confirms the problem is on the high side.

Question 36Commercial Refrigeration

A technician recovers refrigerant from a commercial refrigeration appliance under EPA Section 608. Which requirement applies to the recovery equipment?

  1. It must be certified for the refrigerant type and achieve the required evacuation level Correct answer.
  2. It only needs certification for R-22 systems
  3. It must be vented to the outdoors during recovery
  4. It may be shared between refrigerant types without any change

Explanation

Section 608 requires certified recovery equipment matched to the refrigerant and capable of reaching the mandated vacuum level for the appliance type. Mixing refrigerants in the same recovery cylinder or equipment is prohibited.

Question 37Commercial Refrigeration

A technician needs to verify the charge in a system with a receiver and a sight glass. Which method is most reliable?

  1. Measuring suction superheat only
  2. Checking subcooling at the condenser outlet along with a clear sight glass under stable load Correct answer.
  3. Reading the low-side gauge only
  4. Watching for bubbles in the sight glass only

Explanation

A sight glass can show bubbles from flash gas caused by a restriction or low subcooling, not just undercharge. Measuring subcooling under stable conditions and confirming a clear glass gives a reliable charge indication.

Question 38Commercial Refrigeration

A parallel rack has one compressor with a failed unloader. Which symptom is most likely during part-load operation?

  1. The compressor runs continuously at full capacity without cycling
  2. The compressor cannot reduce capacity, so suction pressure drops and the compressor short-cycles Correct answer.
  3. The condenser subcooling drops to zero
  4. The liquid line solenoid stays closed

Explanation

An unloader allows a compressor to run at reduced capacity at part load. If it fails, the compressor stays at full capacity, pulling suction pressure below setpoint and causing short cycling or oil-pressure issues.

Question 39Commercial Refrigeration

A technician is selecting a refrigerant for a new medium-temperature commercial system and wants the lowest GWP among common HFC/HFO options. Which choice best fits?

  1. R-22
  2. R-448A Correct answer.
  3. R-507A
  4. R-404A

Explanation

R-448A is an HFO/HFC blend with a GWP roughly in the 1,300s, well below R-404A and R-507A, and far below R-22's ozone-depleting HCFC status. It is a common lower-GWP retrofit for medium-temperature racks.

Question 40Commercial Refrigeration

A technician is brazing a joint on a system containing R-448A and has already recovered the charge. What additional step is required before applying heat?

  1. Pressurize the line with compressed air
  2. Pull a deep vacuum before heating the joint
  3. Break the vacuum with dry nitrogen and flow nitrogen during brazing Correct answer.
  4. Fill the line with refrigerant vapor before heating

Explanation

After recovery, the system should be purged with dry nitrogen to displace air and prevent copper oxide scale during brazing. Flowing nitrogen during the braze is the standard practice for any refrigerant system.

Question 41Commercial Refrigeration

A technician finds a suction-line filter with a 15 psi pressure drop on a commercial system. What does this indicate?

  1. The system is low on charge
  2. The filter is bypassing refrigerant normally
  3. The compressor valves are leaking
  4. The filter is restricted and should be replaced Correct answer.

Explanation

A suction filter should show very little pressure drop when clean. A 15 psi drop means the element is clogged, restricting flow to the compressor and reducing capacity while raising superheat.

Question 42Commercial Refrigeration

A technician is evacuating a system and the micron gauge stalls at 1,500 microns and rises slowly after the pump is isolated. What does this indicate?

  1. The micron gauge is reading in the wrong units
  2. Moisture or a leak is present and the system needs further attention Correct answer.
  3. The vacuum pump is oversized for the system
  4. The system is fully evacuated and ready to charge

Explanation

A vacuum that stalls and then rises when isolated indicates either a leak admitting air or moisture boiling off and raising pressure. The system should be leak-checked or a triple evacuation performed before charging.

Question 43Commercial Refrigeration

Which safety hazard is specific to a transcritical CO2 booster system compared with an HFC system?

  1. High pressures above the critical point requiring rated components and pressure relief Correct answer.
  2. Ozone depletion from refrigerant leakage
  3. Flammability of the refrigerant at room temperature
  4. Formation of hydrofluoric acid on contact with moisture

Explanation

Transcritical CO2 operates above the critical pressure, so high-side pressures can exceed 1,000 psig. Components, relief devices, and piping must be rated for these pressures, which is not a concern with HFC systems.

Question 44Commercial Refrigeration

A technician measures 0°F superheat at the evaporator outlet and finds frost on the suction line back to the compressor. What is the best corrective action?

  1. Adjust or replace the TXV to restore proper superheat Correct answer.
  2. Increase the condenser fan speed
  3. Add refrigerant to raise suction pressure
  4. Reduce the defrost frequency

Explanation

Zero superheat with frost on the suction line indicates the TXV is flooding the evaporator and liquid is reaching the compressor. The valve should be adjusted or replaced to restore the specified superheat and protect the compressor.

Question 45Commercial Refrigeration

What is the primary function of a receiver in a commercial refrigeration system?

  1. To store liquid refrigerant and accommodate variations in charge and load Correct answer.
  2. To regulate evaporator pressure
  3. To separate oil from the discharge gas
  4. To remove moisture from the refrigerant

Explanation

The receiver stores liquid refrigerant so the system can supply the TXV under varying load and condenser conditions. It also provides a reservoir for pump-down and charge adjustments.

Question 46Commercial Refrigeration

A medium-temperature walk-in has suction pressure 10 psig below design with normal superheat. What is the most likely cause?

  1. A failed condenser fan
  2. A stuck-open TXV
  3. A restricted liquid line or partially closed valve Correct answer.
  4. An overcharged system

Explanation

Low suction pressure with normal superheat suggests the evaporator is starved of refrigerant, often from a liquid line restriction or a partially closed valve. The TXV is still controlling superheat but has insufficient liquid to feed the coil.

Question 47Commercial Refrigeration

A technician is checking a system with a liquid line sight glass and sees continuous bubbles at the TXV inlet while subcooling is normal. What is the most likely cause?

  1. An overcharge of refrigerant
  2. A restriction or pressure drop causing flash gas in the liquid line Correct answer.
  3. A failed compressor
  4. A stuck-closed liquid line solenoid

Explanation

If subcooling is normal but bubbles appear at the TXV, the liquid is flashing due to a pressure drop in the line, such as a restricted filter drier or undersized line. The charge is not the issue.

Question 48Commercial Refrigeration

A technician is servicing a system with R-717 (ammonia). Which personal protective equipment is essential?

  1. Full-face respirator with ammonia cartridges and chemical-resistant gloves Correct answer.
  2. Sunglasses and cotton gloves
  3. Dust mask and leather gloves
  4. Ear plugs and steel-toe boots only

Explanation

Ammonia is toxic and corrosive to eyes and skin, so a full-face respirator with the correct cartridges and chemical-resistant gloves are required. Eye protection and ventilation are also critical in machinery rooms.

Question 49Commercial Refrigeration

A commercial freezer with an air-cooled condenser shows high head pressure and normal subcooling. Which condition best explains this?

  1. A failed evaporator fan
  2. High ambient temperature or dirty condenser coil reducing heat rejection Correct answer.
  3. A refrigerant undercharge
  4. A restricted liquid line

Explanation

High head pressure with normal subcooling points to reduced condenser heat rejection, such as high ambient or a dirty coil. The condenser cannot reject heat efficiently, so head pressure rises while subcooling remains near normal.

Question 50Commercial Refrigeration

A technician is preparing a pump-down cycle on a walk-in cooler. What is the purpose of the liquid line solenoid valve in this cycle?

  1. To stop refrigerant flow to the evaporator so the compressor can evacuate the low side Correct answer.
  2. To control condenser fan cycling
  3. To bypass the filter drier during pump-down
  4. To regulate evaporator pressure during operation

Explanation

In a pump-down cycle, the liquid line solenoid closes when the thermostat is satisfied, stopping flow to the evaporator. The compressor then runs until the low-pressure control trips, evacuating the low side to prevent liquid migration.