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Engine · 623 questions

Refrigeration AC - USCG Exam Questions

Refrigeration cycles and components, compressors, refrigerants, and marine air conditioning systems.

Every question below is a real U.S. Coast Guard exam question with four choices. Answer one and the correct choice is revealed instantly, with the USCG reference and illustration where the question uses one.

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All Refrigeration AC questions

Questions 301–400 of 623 · page 4 of 7

  1. #510 If the refrigeration compressor crankcase is sweating or frosting and is operating with an unusual noise, what is most likely the cause?
  2. #511 If a refrigeration system were short of refrigerant, besides an elevated box temperature, what would be an observable symptom?
  3. #513 If a refrigeration system, equipped with a reciprocating compressor, has a liquid-line solenoid valve that is leaking during the 'off' cycle, what wou...
  4. #515 If a refrigeration compressor had developed a slightly high suction pressure accompanied with an abnormally low suction temperature, the problem could...
  5. #516 An excessive charge of refrigerant in a thermostatically controlled, air-cooled, refrigeration system using a TXV as an expansion device can cause whi...
  6. #517 If a refrigeration compressor using a thermostat as a primary controller is running continuously without significantly lowering the temperature in the...
  7. #518 Moisture in a refrigeration system can cause which of the following conditions?
  8. #520 An evaporator coil of a single evaporator, air cooled refrigerator is accumulating excessive frost due to a failure of the defrost mechanism. If the r...
  9. #521 In a low pressure refrigeration system, excessive running of the purge recovery unit generally indicates which probable condition?
  10. #522 Which recovery procedure should be used to minimize the loss of oil from the system during the recovery of refrigerant from small appliances such as a...
  11. #523 What is true concerning highly contaminated refrigerant recovered from burned out small appliances?
  12. #524 Technicians servicing small refrigeration appliances can employ what type of recovery equipment?
  13. #525 If passive recovery is used on a small appliance fitted with a capillary tube as a metering device with a non-operating compressor, the recovery shoul...
  14. #528 Why is a purge recovery unit typically fitted on low pressure centrifugal chillers?
  15. #530 How should small appliances with less than three pounds of refrigerant be charged with refrigerant?
  16. #531 Charging liquid HCFC-123 into a system under a deep vacuum could cause what to happen unless necessary precautions are taken?
  17. #532 When a refrigeration system is being topped off with a small amount of refrigerant through the low side with the compressor running, what should be do...
  18. #533 Which of the valves listed is normally closed when charging the refrigeration system through the high side?
  19. #535 For safe storage, the maximum allowable temperature to which refrigerant bottles should be exposed is what temperature?
  20. #536 Overfilling a refrigerant container is extremely dangerous because of the high pressures generated. The generation of pressure is the result of what?
  21. #539 Why can CFC or HCFC refrigerants leaking into a confined space or in limited surroundings cause suffocation?
  22. #540 What is the purpose of running a refrigeration compressor in short intermittent spurts or throttling the suction isolation valve when starting the sys...
  23. #541 When starting a reciprocating refrigeration compressor that has been shut down for a period of time, you should manually throttle which valve?
  24. #548 In general, the thermal bulb for a thermal expansion valve used in a reciprocating air conditioning system is usually charged with what substance?
  25. #558 Which of the following is true concerning the class "D" air conditioning system shown in the following illustration? Illustration GS-RA-42 illustration
  26. #559 Concerning the arrangement of equipment and associated hoses shown in the illustration, which statement is true? Illustration GS-RA-59 illustration
  27. #560 To add small amounts of refrigerant to the low side of an air conditioning system, the refrigerant should be introduced through a particular valve and...
  28. #561 To add refrigerant to the high side of an air conditioning system, you should close the king valve and introduce the refrigerant through what valve in...
  29. #566 Concerning the arrangement of equipment and associated hoses shown in the illustration, which statement is true? Illustration GS-RA-58 illustration
  30. #583 What type of HVAC system is ideally designed to serve a large public space?
  31. #584 What type of HVAC system is characterized by poor air distribution and ventilation and low system heat loads?
  32. #588 What type of HVAC system is characterized by a having a split supply air stream, with one for cold air and the other for hot air?
  33. #589 What type of HVAC system is characterized by having control dampers in locations other than the outside air supply, outside air exhaust, and recircula...
  34. #595 What type of pump is invariably used as a circulator in a hydronic heating system?
  35. #596 What statement is true concerning a one-pipe hydronic heating system?
  36. #597 It is absolutely essential that hydronic heating system hot water piping be kept free of air. Assuming that a system is initially properly filled with...
  37. #599 Concerning cargo-hold dehumidification, what statement is true?
  38. #600 What statement is true concerning a liquid desiccant cargo-hold dehumidification system?
  39. #601 What statement is true concerning a liquid desiccant cargo-hold dehumidification system?
  40. #602 With regard to the cooling and heating coils and humidification and regeneration chambers of a liquid cargo-hold dehumidification system, what stateme...
  41. #603 To prevent damage to dry cargoes, the cargo hold ventilation and dehumidification systems play a key role. In terms of the maintained dew point, what...
  42. #604 To determine the average cargo hold dew point temperature, at what location would the dew point be measured?
  43. #606 What temperature associated with the psychrometric properties of air is measured by an ordinary thermometer?
  44. #616 Which of the hand valve configurations for the gauge manifold set is the correct set up for monitoring both the low and high system pressures? Illustr... illustration
  45. #617 Which of the following leak detectors would be appropriate for use in leak detecting on a system currently pressurized with nitrogen? Illustration GS-... illustration
  46. #619 Some chlorinated fluorocarbon refrigerants may decompose into a toxic irritating gas under what conditions?
  47. #621 If you find a refrigerant leak while using a halide torch, what will happen to the flame as the exploring tube approaches the leak?
  48. #622 Moisture is removed from recovered refrigerant using a recycling machine by what means?
  49. #624 As shown in figure "B" of the illustrated self-contained recovery unit connection diagrams, what is the recovery method supported by the connection sc... illustration
  50. #625 When removing the primary refrigerant from a system using water as a secondary refrigerant, it is important to follow which procedure(s) to safeguard...
  51. #627 A "hygroscopic" lubricant used in refrigeration compressors would have what characteristic?
  52. #628 When checking the oil level in a refrigeration compressor, under what conditions would the most accurate reading be obtained?
  53. #633 Which of the illustrated gauges is capable of measuring vacuums at the micron level for the purpose of proving system dehydration during system evacua... illustration
  54. #634 The coil temperature measured at the expansion valve sensing bulb of an operating system is 10°F. The low side pressure with the compressor runnin... illustration
  55. #635 If the needle and seat assembly is excessively eroded, the valve cage assembly can be replaced. In replacing the original valve cage assembly rated at... illustration
  56. #636 Which of the following illustrated thermal expansion valves would be appropriate to use on an evaporator coil with a 2 psi pressure drop, where extern... illustration
  57. #637 Which of the statements listed is applicable to the thermostatic expansion valve shown in the illustration? Illustration GS-RA-07 illustration
  58. #639 What is one function of the thermal expansion valve used in a refrigeration system?
  59. #640 A thermal expansion valve installed in a refrigeration system is controlled by the action of what device?
  60. #641 When the sensing bulb of a thermostatic expansion valve is charged with a fluid different from the charge used in the system, what name of the charge...
  61. #643 In refrigeration systems with multiple evaporators, the metering of refrigerant to each refrigerated space evaporator is accomplished by what device?
  62. #644 Which of the following illustrated expansion valves is designed to maintain a constant evaporator pressure rather than a constant evaporator superheat... illustration
  63. #645 In a refrigeration system, the bulb for the thermal expansion valve is always located where?
  64. #648 What is the purpose of the pressure transducer as shown in the illustration? Illustration GS-RA-17 illustration
  65. #649 As shown in the illustrated LP centrifugal chiller pressure maintenance system, what is its functional purpose? Illustration GS-RA-40 illustration
  66. #650 A liquid sight flow indicator in a refrigeration system is examined and gas bubbles are noted in motion with the fluid flow. What does this mean?
  67. #651 When a refrigeration compressor motor fails to start, the FIRST thing that should be checked for is what?
  68. #652 A refrigeration system is equipped with a reciprocating compressor and a water-cooled condensing unit. If the system is overcharged, the resulting hig...
  69. #653 An air-cooled refrigerated container unit using R-134a as a refrigerant has a box temperature set point of -15°F, but it is currently operating wi... illustration
  70. #654 One cause of high head pressure occurring in a refrigeration system can be which of the following?
  71. #655 During tests to discover why a refrigeration compressor is running continuously, it is determined that the refrigerated space temperature is slightly...
  72. #656 An increasing head pressure in a refrigeration system, without any corresponding change in the cooling water inlet temperature, would probably be caus...
  73. #657 If a refrigeration system compressor crankcase is exhibiting an unusual degree of sweating or frosting and is operating noisily, what should be done?
  74. #658 If increasing the cooling water flow to a refrigeration condenser fails to lower the condenser pressure, the probable cause may be due to what conditi...
  75. #660 The thermostat controlling the operation of the solenoid valve to a refrigerated box evaporator senses what temperature?
  76. #661 Which of the following statements is true concerning the attached illustration? Illustration GS-RA-12 illustration
  77. #662 Which of the listed operations will cause an automatically controlled refrigeration compressor to restart if the system features a pump down cycle?
  78. #663 What is the purpose of the low-pressure cut-out switch as used as a primary controller for a refrigeration system or unit?
  79. #664 In a refrigeration system featuring low-side pump down prior to the automatic shutdown of the compressor, the temperature of the refrigerated space is...
  80. #665 A container unit's microprocessor-controlled temperature controller is set at -28.9°C, appropriate for a frozen cargo of ice cream. In this mode o... illustration
  81. #666 The sensing line for the low-pressure cutout switch for a refrigeration system is typically connected at what location?
  82. #667 Which of the following electrically operated refrigeration system valves would be most appropriate for use as a 2 position diverting hot gas bypass so... illustration
  83. #669 Which of the conditions listed may be an indication of an excessive amount of refrigerant circulating through the system?
  84. #671 If the refrigeration compressor crankcase is sweating or frosting and is operating with an unusual noise, what is most likely the cause?
  85. #672 If a refrigeration system, equipped with a reciprocating compressor, has a liquid line solenoid valve that is leaking during the 'off' cycle, what wou...
  86. #673 If the running suction pressure at the refrigeration compressor of a TXV controlled air-cooled refrigeration system is below normal, which of the foll...
  87. #674 The color and/or condition of the oil observed in the sight glass of an operating refrigeration compressor experiencing bearing wear or piston scoring...
  88. #675 Leaking suction valves in a refrigeration compressor are indicated by which of the following?
  89. #676 A refrigeration unit will tend to short cycle when operating under what conditions?
  90. #677 An excessive charge of refrigerant in a thermostatically controlled, air-cooled, refrigeration system using a TXV as an expansion device can cause whi...
  91. #678 Which of the listed statements describes the reason why oil foaming occurs when starting a refrigeration compressor?
  92. #679 A reciprocating refrigeration compressor may be tested for leaking discharge valves by stopping the compressor, turning the discharge service valve al...
  93. #680 Unusual noise coming from a refrigeration compressor can be caused by which of the following conditions?
  94. #685 When starting a reciprocating refrigeration compressor that has been shut down for a period of time, you should manually throttle which valve?
  95. #686 What is the drive arrangement of refrigeration compressor shown in figure "B" of the illustration? Illustration GS-RA-41 illustration
  96. #687 When opening or closing compressor service and line isolation valves on a typical refrigeration system that is fitted with packed valves, what must yo...
  97. #689 For most multi-box refrigeration systems, the refrigerant sight glass would be located where in the system?
  98. #690 A liquid indicator sight glass is useful in determining whether or not a refrigeration system is sufficiently charged. Where is it generally located i...
  99. #691 The primary purpose of the liquid line strainer used in a refrigeration system is to prevent dirt and scale from entering what system component(s)?
  100. #700 Zinc plates commonly found in refrigeration systems and used as sacrificial anodes are located where?

Refrigeration AC questions: what to expect

Q How many Refrigeration AC questions are in the Engine pool?

There are 623 Refrigeration AC questions on this site, every one released by the U.S. Coast Guard or taken from the National Maritime Center's sample examinations, with its correct answer. The exam draws its Refrigeration AC module from the same pool.

Q What score do I need to pass the Refrigeration AC module?

Most USCG exam modules, including Refrigeration AC, require 70 percent to pass. Rules of the Road modules require 90 percent.

Q Are these the real USCG Refrigeration AC exam questions?

Yes. They are the published U.S. Coast Guard questions, matched to the National Maritime Center's 2026 sample examinations. Answer any question to see the correct choice, the USCG reference and the illustration where the question uses one.

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