ESCO Light Commercial Refrigeration EXAM with Complete Solutions, Exams of Nursing

Download ESCO Light Commercial Refrigeration EXAM with Complete Solutions and more Exams Nursing in PDF only on Docsity! ESCO Light Commercial Refrigeration EXAM with Complete Solutions 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 does not accumulate. C. sub-cool the compressor. D. ensure proper oil return. --*correct answer*--A. operate at high efficiency. 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. --*correct answer*--A. evaporator superheat. An expansion device that is stuck open will cause: A. low suction pressure B. a starved evaporator. C. excessive superheat D. a flooded evaporator --*correct answer*--D. a flooded evaporator 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. --*correct answer*--A. compressor inlet. (Suction Line) Superheat measurements are best taken: A. during a hot pull down. B. at 8°F to 12°F. C. during defrost. D. with the system operating at design conditions. --*correct answer*--D. with the system operating at design conditions. 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. --*correct answer*--D. a blocked distributor. A TEV with an external equalizer is used on: A. evaporators with a high pressure drop. B. evaporators with a low pressure drop. C. high temperature applications only. D. all evaporators. --*correct answer*--A. evaporators with a high pressure drop. Dry type evaporators operate most efficiently with a 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 --*correct answer*--A. 8° F to 12°F An evaporator used to chill liquids in operating with a normal superheat setting, but the system is not cooling the product properly. Which of the following is the most likely cause? D. inside air dry bulb temperature. --*correct answer*--A. outside air wet bulb temperature. One of the main reasons that reciprocating compressors are not 100% efficient is: A. CFC refrigerants. B. clearance volume. C. evaporator design D. condenser design. --*correct answer*--B. clearance volume. An open drive compressor is most likely to develop a refrigerant leak at the: A. valve plate. B. suction service valve. C. discharge service valve. D. shaft seal. --*correct answer*--D. shaft seal. Multiple compressors provide: A. positive on return. B. lower humidity in high humidity locales. C. capacity control D. zone control. --*correct answer*--C. capacity control 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. --*correct answer*--B. low compression ratios. The thermostatic expansion valve (TEV) maintains a constant _____ in the evaporator. A. temperature B. pressure C. liquid level D. superheat --*correct answer*--D. superheat The automatic expansion valve (AEV) maintains a constant _____ in the evaporator. A. temperature B. pressure C. liquid level D. superheat --*correct answer*--B. pressure 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. --*correct answer*--A. after the capillary tube suction line heat exchanger. A _____ is usually required for ultra-low temperature applications. A. cooler B. comfort cooling system C. freezer D. cascade system --*correct answer*--D. cascade system A defrost cycle can be initiated by a: A. timer. B. defrost thermostat. C. pressure control. D. control thermostat --*correct answer*--A. timer. A defrost cycle can be terminated by the: A. low ambient control. B. condensing temperature. C. head pressure. D. suction pressure. --*correct answer*--D. suction pressure. A defrost cycle is required whenever the evaporator must operate below: A. 0°F B. 32°F C. 10°F D. 20°F --*correct answer*--B. 32°F Excessive frost on the evaporator causes: A. increased efficiency. B. reduced heat transfer. C. high humidity. D. increased superheat. --*correct answer*--B. reduced heat transfer. Automatic pump down systems are used to prevent: A. power surges on demand utility systems. B. surges of liquid refrigerant (slugging) during shut-down. C. oil foaming at shut-down. D. migration of refrigerant to the crankcase during off cycles. --*correct answer*--D. migration of refrigerant to the crankcase during off cycles. An automatic pump down system requires a: A. liquid line solenoid. B. suction accumulator. C. thermostatic cut-out D. fan cycle switch. --*correct answer*--A. liquid line solenoid. Short cycling during pump down can be caused by: A. a leaking compressor suction valve. B. a leaking TEV seat. C. air in the system. D. a leaking cylinder unloading device. --*correct answer*--A. a leaking compressor suction valve. A _____ type metering device is best suited in applications where freeze protection is required. C. as a liquid through a throttling valve into the high side. D. as a vapor into the low side. --*correct answer*--B. as a liquid, through a throttling valve into the low side. A refrigeration system used to cool another refrigeration system is called a: A. piggyback system B. cascade system. C. twin system. D. parallel system. --*correct answer*--B. cascade system. To achieve peak efficiency and performance in a Capillary tube system: A. attach an auxiliary heat exchanger to the liquid line to provide extra flash gas. B. solder the capillary tube to the liquid line. C. remove 5" inches of insulation from the suction line. D. the system must be critically charged. --*correct answer*--D. the system must be critically charged. Expendable refrigerant means: A. it is the most expensive refrigerants. B. it cannot be released to the atmosphere. C. it can only be recovered once. D. it can be used one time. --*correct answer*--D. it can be used one time. If a walk-in cooler requires a high percentage of moisture in the air due to the product being stored, the logical evaporator TD would be: A. 10 degrees B. 20 degrees C. 30 degrees D. 40 degrees --*correct answer*--B. 20 degrees "Pump down" means to capture system refrigerant in the: A. recovery cylinder. B. compressor. C. condenser and/or liquid receiver. D. suction accumulator. --*correct answer*--C. condenser and/or liquid receiver. What is the normal operating position for two-way service valves? A. Front seated B. Back seated C. Cracked D. Closed --*correct answer*--B. Back seated The suction accumulator prevents liquid refrigerant from entering the: A. evaporator. B. condenser. C. compressor. D. heat exchanger. --*correct answer*--C. compressor. When a service valve is back seated, which port is closed? A. Outlet port. B. Inlet port. C. Service port. D. Pilot port. --*correct answer*--C. Service port. When work on a refrigeration system is complete, the service valves should be in this position: A. back seated. B. front seated. C. cracked. D. midpoint. --*correct answer*--A. back seated. What type of oil is used with HFC refrigerant? A. Alkylbenzene B. Mineral C. Ab / min D. Polyol ester --*correct answer*--D. Polyol ester A low pressure switch can be used for: A. overcharge protection. B. high side cut-out. C. control refrigerant flow rate. D. control of space temperature. --*correct answer*--D. control of space temperature. What valve is used to connect multiple evaporators of different temperatures to a single compressor? A. Crankcase pressure regulator (CPR). B. Evaporator pressure regulator (EPR). C. Oil pressure regulator. D. Head pressure regulator. --*correct answer*--B. Evaporator pressure regulator (EPR). What valve is used to prevent evaporator pressure from falling below a set limit? A. Crankcase pressure regulator (CPR). B. Evaporator pressure regulator (EPR). C. Oil pressure regulator. D. Head pressure regulator. --*correct answer*--B. Evaporator pressure regulator (EPR). 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. Crankcase pressure regulator (CPR). D. Oil pressure regulator. --*correct answer*--C. Crankcase pressure regulator (CPR). A multiple compressor system uses individual pressure controls for each: A. evaporator. Vibration eliminators should be installed _____ to the compressor crankshaft centerline. A. Perpendicular B. parallel C. vertical D. at a 90° angle --*correct answer*--B. parallel With blended refrigerants, the difference between the boiling point (bubble point) and condensing point (dew point) is called: A. temperature slip. B. temperature glide. C. temperature rate. D. electraglide. --*correct answer*--B. temperature glide. On a rack of multiple compressors, each compressor is controlled by: A. suction pressure transducer. B. thermostat. C. interstage pressure. D. Crankcase Pressure Regulating valve (CPR). --*correct answer*--D. CPR valve. Which refrigerant line is most sensitive to Improper sizing? A. Liquid line. B. Suction line. C. Discharge line. D. Condensate line. --*correct answer*--A. Liquid line. What Is the most likely cause of the following symptoms? The compressor shuts off on the oil pressure switch. The oil sight glass is 1/2 full. Suction pressure is 3 psig (R-502). Oil pressure is 70 psig. A. Defective oil pump. B. Insufficient oil. C. Defective oil pressure switch. D. Suction pressure too low. --*correct answer*--D. Suction pressure too low. A Michigan servicemen is called 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 OK, 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 drier. --*correct answer*--B. Faulty condenser ambient controls. 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. --*correct answer*--D. Defective defrost timer. At what evaporator temperature does an Ice maker begin to make ice? A. 32°F B. 0°C C. 0°F D. 20°F --*correct answer*--D. 20°F A solenoid valve (N.C.), energized during the run cycle, is often used in the oil return line between the separator and the compressor crankcase for the purpose of: A. Isolating the separator from the low side during the off cycle In the event of a leaking ball and float assembly. B. preventing migration of refrigerant to the separator during the off cycle. C. allowing the separator to return oil to the crankcase during the off cycle only. D. allowing the system to equalize during the off cycle. --*correct answer*-- D. allowing the system to equalize during the off cycle. Defrostlng a low temperature evaporator can be accomplished by: A. stopping the evaporator fan motor. B. reversing the compressor rotation. C. using electric heaters. D. installing a modulating valve. --*correct answer*--C. using electric heaters. 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. low refrigerant charge. B. defective valves in the compressor. C. refrigerant overcharge. D. product overload. --*correct answer*--A. low refrigerant charge. Bubbles or foaming In the compressor's oll sight glass are an indication of: A. low oil level condition. B. refrigerant In the oil. C. too much oil in the crankcase. D. moisture in the oil. --*correct answer*--B. refrigerant In the oil. What is the viscosity of most oils used in refrigeration systems? A. 100 B. 200 C. 300 D. 400 --*correct answer*--A. 100 A customer complains that their counter top ice machine is making a loud noise and not producing any ice. Upon arrival, the technician removes the front panel and determines that the noise is coming from the ice machine auger. Before the technician can unplug the power supply, the auger drive motor overload opens and the drive motor stops. The machine's compressor continues to operate. The technician unplugs the ice machine and attaches 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 attempts to reset the switch. The switch will not reset and the motor frame is very hot. Using ice from another machine in a heavy plastic bag, the motor is coo -- *correct answer*--C. the lack of water flow reduced evaporator load, which resulted in the auger freezing up and the drive motor tripping the overload. The low pressure and current are the result of low load on the evaporator. Water flow must be restored and the machine should operate properly. A customer calls and 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 bell of Ice. The technician decides to advance the electromechanical defrost timer to the next defrost period and observe the defrost function. In doing so, the evaporator defrosts to the level of the ice build-up, 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 sec --*correct answer*--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 force to damage the flare, creating a slow refrigerant leak. 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 confirms the owner's complaint of thin ice and low production. Further inspection reveals that the ice machine Is equipped with a harvest solenoid and a thermostatic expansion valve. The water pump is operating and the water reservoir is clean and free of debris. A check of the water temperature in the reservoir is 32°F. The technician decides to install manifold gauges and check system pressures. This Indicates slightly elevated suction pressure with the discharge pressure at or near normal for the application and refrigerant used. A check of evaporator superheat shows it to be 15°F to 18°F. A check of temperature difference across the harvest solenoid indicates a temperature rise of approximately 10°F. A check of condenser sub cooling ind --*correct answer*--D. the harvest solenoid ls leaking. keeping the suction pressure above normal, and must be replaced. An oil separator must be kept warm in order to: A. prevent sluggish return of the oil to the crankcase. B. prevent refrigerant from condensing in the separator during the off cycle. C. keep the oil at the same temperature as the oil in the crankcase. D. operate properly when exposed to low outdoor ambient. --*correct answer*--A. prevent sluggish return of the oil to the crankcase. If a pressure control has been adjusted to cut-in at 40 psig, in order to have a 15 psig cut-out, the differential setting of the control must be: A. 55 B. 35 C. 25 D. 15 --*correct answer*--C. 25 Should liquid refrigerant accumulate in the oil separator, it will be returned to the crankcase with the oil. If this occurs it will result in: A. a stalled compressor due to excess vapor pressure in the crankcase. B. raising the oil level in the crankcase to a dangerous level. C. increased temperature of compressor components. D. dilution of the oil and foaming in the crankcase. --*correct answer*--D. dilution of the oil and foaming in the crankcase. When retrofitting a CFC/mineral oil system to an HFC based refrigerant: A. changing to another type of oil Is not required. B. you must add an alkylbenzene oil. C. you must add a napthenlc oil. D. extensive oil flushing is required. --*correct answer*--D. extensive oil flushing is required. Ester based oils are: A. aromatic blends. B. vegetable in origin. C. a synthetic oil. D. not a popular choice for retrofit. --*correct answer*--C. a synthetic oil. When measuring oil pressure on a 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.