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Refrigeration System Troubleshooting, Exams of Refrigeration and Air Conditioning

University College of London (UCL)Refrigeration and Air Conditioning

Various aspects of refrigeration system troubleshooting, including evaporator superheat, expansion devices, evaporator operation, defrost cycles, pressure controls, and compressor oil management. It provides detailed explanations and solutions to common issues that can arise in commercial and industrial refrigeration systems. The information presented can be useful for hvac/r technicians, students, and anyone interested in understanding the principles and troubleshooting techniques for refrigeration systems. A wide range of topics, from identifying the causes of evaporator freeze-ups to understanding the role of oil separators and compression ratios. By studying this document, readers can gain a comprehensive understanding of the key components and their interactions within a refrigeration system, enabling them to effectively diagnose and resolve various system malfunctions.

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2023/2024

Available from 09/27/2024

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ESCO Light Commercial Refrigeration EXAM
with Verified Solutions 2024-2025 Latest
Approved.
1. In a dry type (direct expansion) evaporator, liquid refrigerant must boil
away as close to the end of the coil as possible in order to:
A. Operate at high-efficiency
B. Ensure that Frost is not accumulate
C. Sub cool the compressor
D. Ensure proper oil return - Solution A. Operate at high-efficiency
2. The difference between the temperature of the refrigerant boiling in the
evaporator and the temperature at the evaporator outlet is known as
A. Evaporator superheat
B. Latent heat
C. Evaporator sub-cooling
D. Sublimation - Solution A. Evaporator superheat
3. An expansion device that is stuck open will cause
A. Low suction pressure
B. A starved evaporator
C. Excessive superheat
D. A flooded evaporator - Solution D. A flooded evaporator
4. When measuring evaporator superheat on a commercial system that has
a long suction line, the pressure reading should be taken at the
A. Compressor inlet
B. Evaporator outlet
C. Condenser outlet
D. Receiver Inlet - Solution A. Compressor inlet
5. Superheat measurements are best taken
A. During a hot pulldown
B. At 8°F two 12°F
C. During defrost
D. With the system operating at design conditions - Solution D. With the
system operating at design conditions
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Download Refrigeration System Troubleshooting and more Exams Refrigeration and Air Conditioning in PDF only on Docsity!

ESCO Light Commercial Refrigeration EXAM

with Verified Solutions 2024-2025 Latest

Approved.

  1. In a dry type (direct expansion) evaporator, liquid refrigerant must boil away as close to the end of the coil as possible in order to: A. Operate at high-efficiency B. Ensure that Frost is not accumulate C. Sub cool the compressor D. Ensure proper oil return - Solution A. Operate at high-efficiency
  2. The difference between the temperature of the refrigerant boiling in the evaporator and the temperature at the evaporator outlet is known as A. Evaporator superheat B. Latent heat C. Evaporator sub-cooling D. Sublimation - Solution A. Evaporator superheat
  3. An expansion device that is stuck open will cause A. Low suction pressure B. A starved evaporator C. Excessive superheat D. A flooded evaporator - Solution D. A flooded evaporator
  4. When measuring evaporator superheat on a commercial system that has a long suction line, the pressure reading should be taken at the A. Compressor inlet B. Evaporator outlet C. Condenser outlet D. Receiver Inlet - Solution A. Compressor inlet
  5. Superheat measurements are best taken A. During a hot pulldown B. At 8°F two 12°F C. During defrost D. With the system operating at design conditions - Solution D. With the system operating at design conditions
  1. A technician is checking the superheat on a multi circuit evaporator and finds one of the circuits has a superheat that is higher than the others. This could be caused by A. A dirty coil B. A refrigerant overcharge C. Uneven air distribution D. A blocked distributor - Solution D. A blocked distributor
  2. A TXV with an external equalizer is used on A. Evaporators with a high pressure drop B. Evaporators with a low pressure drop C. High temperature application is only D. All evaporators - Solution A. Evaporators with a high pressure drop
  3. Dry type evaporators operate most efficiently with the superheat setting of approximately A. 8°F to 12°F B. 13°F to 19°F C. 20°F to 30°F D. 31°F to 40°F - Solution A. 8°F to 12°F
  4. An evaporator used to chill liquids is operating within normal superheat setting. But the system is not cooling the product properly. Which of the following is most likely the cause? A. Overcharge of refrigerant B. Undercharge of refrigerant C. The circulator D. The TXV - Solution A. Overcharge of refrigerant
  5. What time interval is required between each superheat adjustment? A. Not less than one hour B. About 10 to 15 minutes C. At least a half hour D. No time delay - Solution B. About 10 to 15 minutes
  6. A low temperature evaporator used for cooling space or product refrigeration A. Is the same as one used for medium or high temperatures B. Must have fins space closer together
  1. Workable head pressure during periods of low ambient temperature can be achieved by using A. An economizer B. Evaporator dampers C. Evaporator flooding D. Fan cycle control - Solution D. Fan cycle control
  2. Cooling towers that pass air over water to remove system heat are limited in capacity by A. Outside air wet bulb temperature B. Outside air dry bulb temperature C. Inside air wet bulb temperature D. Inside air dry bulb temperature - Solution A. Outside air wet bulb temperature
  3. Parallel compressors often referred to as a rack system may use A. A common suction, but not a common discharge header B. A common discharge header, but not a comment section header C. Both comment section header and common discharge header D. A common accumulator, but never a common receiver - Solution A. A common suction, but not a common discharge header
  4. The major difference between a cooling tower and an evaporative condenser is A. Location based on prevailing winds in the angle of the sun B. The only real difference is design and operating controls of the water flow C. The refrigerant is cool directly in a cooling tower D. The refrigerant is indirectly cooled in the cooling tower - Solution D. The refrigerant is indirectly cooled in the cooling tower
  5. Multiple compressors provide A. Positive oil return B. Lower humidity and high humidity locales. C. Capacity control D. Zone control - Solution C. Capacity control
  6. A dirty evaporator and subsequent low evaporator pressures will cause A. High compression ratios B. Low compression ratios

C. High head pressure D. High suction pressure - Solution B. Low compression ratios

  1. The thermostatic expansion valve (TEV) maintains a constant _______ in the evaporator. A. Temperature B. Pressure C. Liquid level D. Superheat - Solution D. Superheat
  2. What type of ice is made with the commercial icemaker that uses a gear motor and auger? A. Crescent cube ice B. Shaved ice C. Cell type of ice D. Block ice - Solution B. Shaved ice
  3. Some capillary tube systems take advantage of heat exchange by soldering the capillary tube to the suction line. In order to obtain the correct superheat reading, it must be taken A. After the capillary tube suction line heat exchanger B. Before the capillary tube suction line heat exchanger C. Before the suction line enters the compressor D. On the capillary tube as it enters the evaporator - Solution A. After the capillary tube suction line heat exchanger
  4. A ______ is usually required for ultra-low temperature applications. A. Cooler B. Comfort cooling system C. Freezer D. Cascade system - Solution D. Cascade system
  5. A hot gas defrost cycle can be initiated by a A. Timer B. Defrost thermostat C. Pressure control D. Control thermostat - Solution A. Timer
  6. When the defrost cycle is terminated, the evaporator fans will A. Immediately come on

C. Limits the pressure in setpoint of a thermostatic expansion valve (TXV). D. Is used with the capillary tube system to prevent high suction pressure - Solution B. Limits pressure setpoint in the evaporator

  1. The "low ambient control" is used to control A. Suction pressure B. Head pressure C. Evaporator fans D. Compressor - Solution B. Head pressure
  2. The crankcase heater is used to prevent A. Refrigerant migration to the compressor crankcase during the off cycle B. High compressor superheat under low ambient conditions C. Prevent liquid flood back to the compressor D. Refrigerant migration to the compressor crankcase - Solution A. Refrigerant migration to the compressor crankcase during the off cycle
  3. The type of compressor that allows access to the internal components is the A. Hermetic B. Scroll C. Semi hermetic D. Rotary - Solution C. Semi hermetic
  4. Low ambient temperatures seriously affect A. Water cooled units B. Air cooled units C. Compressors D. Dairy coolers - Solution A. Water cooled units
  5. Water cooling towers require a periodic blow down to control A. Rainwater B. PH level above 20 C. Water overflow D. Scaling - Solution D. Scaling
  6. High temperature refrigeration applications normally provide box temperatures of A. 47°F to 60°F B. 28°F to 40°F

C. 60°F to 75°F D. 30°F to 45°F - Solution A. 47°F to 60°F

  1. Medium temperature refrigeration applications will normally provide box temperatures of A. 20°F to 40°F B. 25°F to 42°F C. 28°F to 40°F D. 30°F to 42°F - Solution D. 30°F to 42°F
  2. Low temperature refrigeration applications, other than ice makers, will normally provide box temperatures of A. 0°F to 32°F B. 0°F to -20°F C. -10°F to 32°F D. -40°F to 0°F - Solution A. 0°F to 32°F
  3. What is the purpose of an oil separator? A. To capture oil and prevent it from traveling throughout the system B. To clean the oil and separate the refrigerant from it C. To filter all of the oil leaving the evaporator D. To prevent evaporator freeze up - Solution A. To capture oil and prevent it from traveling throughout the system
  4. Blended refrigerants should be charged into a running system A. As a vapor into the high side B. As a liquid through a throttling valve into the low side C. As a liquid through a throttling valve into the high side D. As a vapor into the low side - Solution B. As a liquid through a throttling valve into the low side
  5. A refrigeration system that uses the evaporator of the first stage to exchange heat with the condenser of the second stage refrigeration system is called a A. Piggyback system B. Cascade system C. Twin system D. Parallel system - Solution B. Cascade system
  6. To achieve peak efficiency and performance in a capillary tube system,
  1. When the compressor service valve is back seated, which port is closed? A. Outlet port B. Inlet port C. Service port D. Pilot port - Solution C. Service port
  2. When work on a refrigerator is complete, the compressor service valves should be in what position? A. Back seated B. Front seated C. Cracked D. Midpoint - Solution A. Back seated
  3. What type of oil is used with HFC refrigerant? A. Alkyl-benzene B. Mineral C. Flax seed D. Polyol Esther - Solution A. Alkyl-benzene
  4. On an expansion valve refrigeration system, a low pressure control can indirectly be used for A. Overcharge protection B. High side cut out C. Control refrigerant flow rate D. Controlling box temperature - Solution D. Controlling box temperature
  5. What valve is used to connect multiple evaporators of different temperatures to a single compressor? A. Crank case pressure regulator (CPR) B. Evaporator pressure regulator (EPR) C. Oil pressure regulator D. Head pressure regulator - Solution B. Evaporator pressure regulator (EPR)
  6. What valve is used to prevent evaporator pressure from falling below a set limit? A. Crank case pressure regulator (CPR) B. Evaporator pressure regulator (EPR) C. Oil pressure regulator

D. Head pressure regulator - Solution B. Evaporator pressure regulator (EPR)

  1. What valve is used to control excessive pressure entering the compressor during a hot pull down? A. Head pressure regulator B. Evaporator pressure regulator (EPR) C. Crank case pressure regulator (CPR) D. Oil pressure regulator - Solution C. Crank case pressure regulator (CPR)
  2. The oil return orifice inside a suction line accumulator is designed to A. Return oil only during the off cycle back to the compressor B. Maintain the same pressure in the evaporator to the inlet of the compressor C. Meter liquid refrigerant and oil at acceptable rate D. Equalize discharge and suction pressures during off cycle - Solution C. Meter liquid refrigerant and oil at acceptable rate
  3. Why do suction line filter dryer's have two service ports? A. To help remove acid trapped in the dryer B. To enable checking pressure drop across the dryer C. One port is used for charging with liquid, the other is used for charging with vapor D. One port is used for adding oil, the other poor is used for adding vapor to the system - Solution B. To enable checking pressure drop across the dryer
  4. A thermostatic expansion valve (TXV) that creates an unstable suction pressure is said to be A. Flashing B. Modulating C. Hunting D. Fractionating - Solution C. Hunting
  5. Head pressure control valves permit hot gas to travel directly to the A. Condenser B. Evaporator C. Liquid receiver D. TXV - Solution B. Evaporator
  1. Capacity control of a large compressor can be performed with A. Solenoid valve B. Hand valves C. Unloaders D. Dampers - Solution C. Unloaders
  2. Vibration eliminator's should be installed _______ to the compressor crankshaft centerline. A. Perpendicular B. Parallel C. Vertical D. At a 90° angle - Solution A. Perpendicular
  3. What pH level is considered neutral and desired for ice machine or cooling tower applications? A. 5 B. 7 C. 9 D. 10 - Solution B. 7
  4. On a rack of multiple compressors, each compressor is controlled by A. Suction pressure transducer B. Thermostat C. Interstage pressure D. CPR valve - Solution D. CPR valve
  5. Which refrigerant line is most sensitive to improper sizing? A. Liquid line B. Suction line C. Discharge line D. Condensate line - Solution A. Liquid line
  6. What is the most likely cause of the following symptoms? The compressor shuts off on the oil pressure switch. The oil sightglass is one half full. Suction pressure is 3 psig (R-502). A. Defective oil pump B. Insufficient oil C. Defective oil pressure switch D. Suction pressure too low - Solution D. Suction pressure too low
  1. A Michigan service man is called a to a supermarket on a cold winter day because all the frozen food is melting. A low temperature rack of five compressors control the frozen food and ice cream units. Power supply is okay, but all compressors are off. All five low pressure controls are open. The liquid receiver shows full. The hot gas discharge line is cold because the condenser is on the roof. What is the likely cause of the trouble? A. A faulty liquid line service valve B. Faulty condenser ambient controls C. Defective pump down solenoid D. A plugged filter dryer - Solution B. Faulty condenser ambient controls
  2. A string of five frozen food cases are operated by one compressor. All five cases are iced up. What is the likely problem? A. Low refrigerant charge B. Defective thermostat C. Plugged condensate drain D. Defective defrost timer - Solution A. Low refrigerant charge
  3. At what evaporative temperature does an icemaker begin to make ice? A. 32°F B. 0°C C. 0°F D. 20°F - Solution C. 0°F
  4. What device is used to check for parallel misalignment of a motor coupling? A. Dial indicator B. Alignment-Techno meter C. Level and precision ruler D. Caliper and parallel level - Solution A. Dial indicator
  5. Defrosting a low temperature evaporated can be accomplished by A. Stopping the evaporator fan motor B. Reversing the compressor rotation C. Using electric heaters D. Installing a modulating valve - Solution C. Using electric heaters
  6. A system that uses an automatic expansion valve (AEV) is not cooling enough and running continuously. The gauges reveal low head pressure, but the suction pressure is acceptable. This could be caused by

A. There is too much oil in the system B. The replacement filter dryer is larger than the original C. Ambient temperature is 95°F D. Ambient temperature is 72°F - Solution B. The replacement filter dryer is larger than the original

  1. A restaurant owner has indicated that their walk in cooler is running above normal temperatures and seems to be running all the time. Upon initial visual inspection, the technician finds that all evaporator fans are running properly and the thermostat is calling for cooling. Further inspection reveals that the evaporator has a heavy accumulation of ice on the top of one third of the coil. Measuring the evaporator superheat, the technician finds that it is 22°. A check of system pressures indicates lower than normal suction and discharge pressures. A check of condenser subcooling shows 2°. The technician determines that A. The evaporator is flooded due to an overcharge of refrigerant B. The evaporator is starved due to a partial loss of refrigerant charge C. The evaporator is operating properly, but a defrost problem exists D. The TXV sensing bulb has probably lost its charge and must be replaced - Solution B. The evaporator is starved due to a partial loss of refrigerant charge
  2. A customer calls and indicates that he has a walk-in freezer that is cutting on and off after a very short run time on a repeated basis. He indicates that he had a higher than normal power bill the previous month and thinks that the unit's erratic behavior may have contributed to the higher bill. The technician arrives in inspects the freezer. The freezer box temperature is -10°F, and the condensing unit is off. However, the technician observes the condensing unit operate and short cycle several times within a few minutes of the demand being satisfied. The technician shut the unit down, blocking and tagging the disconnect. This system is equipped with both low and high pressure switches, a suction line accumulator, and a liquid line solenoid. The technician notices that there is ice buildup from the outlet of the liquid line solenoid to the expansion valve. Manifold gauges are attached to the service ports. Remo - Solution D. The accumulator contains liquid refrigerant and the surrounding temperature vaporizes the liquid, causing the low pressure switch to close prematurely
  1. A customer complains that their countertop ice machine is making a loud noise and not producing any ice. Upon arrival, the technician removes the front panel and determines that the noises coming from the ice machine auger. Before the technician can unplug the power supply, the auger drive motor overload opens in the drive motor stops. The machine's compressor continues to operate. The technician unplugs the ice machine and attach his gauges to the low and high side service ports. In addition, a clamp on ammeter is placed on the power lead to the compressor. The technician turns the power switch to the off position and plugs the ice machine back into the power supply. The technician locates the manual reset switch located on top of the auger drive motor and attempt to reset the switch. The switch will not reset and the motor frame is very hot. Using ice from another machine in the heavy plastic bag, the motor is - Solution C. The lack of water flow reduced evaporator load, which resulted in the auger freezing up and the drive motor tripping the overload. The lower pressures and current are the result of low load on the evaporator. Waterflow must be restored and machine should operate properly.
  2. A customer calls it indicates that a walk-in freezer is running gradually higher box temperature. The technician finds the box at 15°F, the thermostat is set properly for a freezer application, and the condensing unit is operating, but not cycling after adequate pull down time. An inspection of the evaporator reveals heavy ice accumulated across the top two rows, and the entire body of the thermostatic expansion valve and power element frozen in a ball of ice. The technician decides to advance the electromechanical defrost timer to the next defrost. And observe the defrost function. In doing so, the evaporator defrosts to the level of the ice buildup, but no further. All power to both the freezer and condensing unit is removed, locking and tagging each disconnect. The technician then defrosts the remainder of the ice from the evaporator and expansion valve body. All evaporator housings are placed back and secure - Solution B. Over a period of time, moisture had gathered under the flare nut on the evaporator side of the expansion valve. Repeated freezing and thawing had created enough for us to damage the flare, creating a slow refrigerant leak.
  3. A customer is experiencing low ice production in a cube type ice machine. Symptoms include long run cycle, thin or smaller cubes, and low production. The initial visual inspection confirmed the owners complaint of

D. Extensive oil flushing is required - Solution D. Extensive oil flushing is required

  1. Esther based oils are A. Aromatic blends B. Vegetable and origin C. A synthetic oil D. Naot a popular choice for retrofit - Solution C. A synthetic oil
  2. When measuring oil pressure on the compressor with a pressurized oiling system, A. Actual oil pressure can be read directly from the oil pressure gauge B. Actual oil pressure must be calculated by subtracting suction pressure from the oil pressure gauge reading C. Actual oil pressure must be calculated by adding suction pressure to the oil pressure gauge reading D. Actual oil pressure is not important because it is a pressurize system - Solution B. Actual oil pressure must be calculated by subtracting suction pressure from the oil pressure gauge reading
  3. The term "refrigerant conditions" refer to which of the following? A. Saturated, superheated, or sub cooled refrigerant B. Pressurized refrigerant only C. A system in a complete vacuum D. The outdoor ambient temperature - Solution A. Saturated, superheated, or sub cooled refrigerant
  4. A water regulating valve used to control water flow in a water cooled condenser application can be most accurately adjusted by A. Adjusting the valve to the manufacturers stated flow rate and PSI per minute B. Adjusting the valves to the design condensing temperature C. Adjusting the valve to the system low side pressure required for the application D. Adjusting the valve to the running load ampere draw of the compressor - Solution B. Adjusting the valves to the design condensing temperature
  5. An oil pressure differential switch utilizes which of the following pressures in opening the context of the time delay heater? A. System suction and discharge pressures

B. Sensing bulb and suction pressure C. Sensing bulb and discharge pressure D. Compressor crankcase pressure and oil pump discharge pressure - Solution D. Compressor crankcase pressure and oil pump discharge pressure

  1. The two manually adjust the parameters of a high-pressure switch are A. Spring tension and snap action B. Differential and cut out C. Cut in and cut out D. Differential and cut in - Solution C. Cut in and cut out
  2. The term "cryogenics" refers to refrigeration systems operating at what temperature range? A. 0°F to -35°F B. -40°F to -75°F C. -100°F to -175°F D. -250°F to -450°F - Solution D. -250°F to -450°F