Refrigeration & AC - 1st Asst/Chief

The correct answer is B) discharge of the compressor lube oil pump. The fluid used as a source of actuating power against the underside of the unloader power element piston of the refrigeration compressor capacity control mechanism is obtained from the discharge of the compressor lube oil pump. This pump circulates lubricating oil throughout the compressor, and a portion of this pressurized oil is diverted to provide the necessary hydraulic force to actuate the unloader mechanism and control the compressor capacity. The other options are incorrect because: A) the gas discharge from the compressor would not provide the necessary hydraulic power; C) the high side liquid receiver does not contain a pressurized fluid source; and D) a secondary hydraulic pump is not typically used for this purpose in standard refrigeration compressor capacity control systems.

The correct answer is C) the highest. When all the evaporators of a four-box refrigeration system are actively being fed with liquid refrigerant, the control oil pressure acting on the hydraulic relay piston will be at its highest value. This is because as the refrigeration load increases with all evaporators in use, the compressor capacity control system will need to increase the compressor displacement to meet the higher demand. This increase in compressor displacement requires the control oil pressure to be at its maximum to ensure the hydraulic relay piston is positioned to allow the compressor to operate at its highest capacity. The other options are incorrect because the control oil pressure would not be at its lowest (A) or mid-range (B) when the refrigeration load is at its highest, and the lube oil system is indeed relevant to the operation of the capacity control unloader (D).

The correct answer is B) With a condenser fitted with a single fan driven by a multi-speed electric motor, the fan speed would decrease under low ambient temperature conditions. The reasoning behind this is that in a refrigeration system with an air-cooled condenser, the fan cycling control pressure switch is designed to maintain the proper high-side pressure by adjusting the fan speed. When the ambient temperature is low, the condenser is able to reject heat more efficiently, causing the high-side pressure to decrease. The fan cycling control pressure switch will then reduce the fan speed to prevent the high-side pressure from dropping too low, which could lead to other issues in the system. The other options are incorrect because they do not accurately describe the behavior of the fan cycling control pressure switch in response to changes in ambient temperature. Option A is incorrect because the fan speed would increase, not decrease, under high ambient temperature conditions. Options C and D are incorrect because they do not apply to a system with a single fan driven by a multi-speed motor.

The correct answer is D) head pressure regulating valve. The valve shown in the illustration is used to regulate the head pressure in the refrigeration system. The head pressure is the pressure on the high-pressure side of the refrigeration cycle, which is maintained by the compressor. The head pressure regulating valve helps to control this pressure to ensure efficient operation of the system. The other answer choices are incorrect because: A) A thermostatic expansion valve is used to control the flow of refrigerant into the evaporator, not the head pressure. B) A suction pressure regulating valve is used to control the pressure on the low-pressure side of the system, not the head pressure. C) An evaporator pressure regulating valve is also used to control the low-pressure side, not the high-pressure side.

The correct answer is B) "2". The set point adjustment of the device shown in the illustration GS-RA-14 is made by rotating component "2". This is typically the knob or dial used to adjust the desired set point or threshold value for the device. The other components labeled "1", "3", and "4" are likely related to the overall operation and function of the device, but do not directly control the set point adjustment. The other answer choices are incorrect because they do not correspond to the component responsible for adjusting the set point, as indicated in the illustration.

The correct answer is A) "2" should be turned to further compress the spring. To increase the operating head pressure of the refrigeration system, the spring-loaded valve (item "2" in the illustration) must be adjusted to increase the compression of the spring. This will raise the pressure at which the valve opens, resulting in a higher operating head pressure in the system. The other options are incorrect because: B) Relaxing the spring compression would decrease the operating head pressure. C) Compressing the bellows (item "4") would not directly affect the spring-loaded valve that controls the head pressure. D) Relaxing the bellows would also not impact the spring-loaded valve.

The correct answer is B) X. The high pressure cutout is indicated by component X in the illustration GS-RA-12. This component is responsible for shutting off the engine or fuel supply when the system pressure exceeds a certain threshold, preventing damage to the engine or fuel system. This feature is a critical safety mechanism required by the US Coast Guard regulations for vessels operating under a Captain's License. The other lettered components, W, Y, and Z, likely represent other essential parts of the fuel or engine system, but they do not specifically indicate the high pressure cutout function.

The correct answer is D) 80 degrees F. To determine the wet bulb temperature, we need to use the given dry bulb temperature (90 degrees F) and the relative humidity (65%). Using a psychrometric chart or a wet bulb temperature calculator, the wet bulb temperature corresponding to a dry bulb temperature of 90 degrees F and a relative humidity of 65% is approximately 80 degrees F. The other answer choices are incorrect because: A) 62 degrees F is too low for the given conditions. B) 63 degrees F is too low for the given conditions. C) 77 degrees F is slightly lower than the correct answer of 80 degrees F.

The correct answer is B) When recovering refrigerant from the centrifugal chiller using this method, it minimizes the risk of chiller tube freeze-up. The arrangement of equipment and associated hoses shown in the illustration is designed to safely recover refrigerant from a centrifugal chiller. The key benefit of this method is that it helps prevent the chiller tubes from freezing up during the recovery process, which can damage the equipment. This is achieved by maintaining a proper flow and pressure balance within the system. The other options are incorrect because: A) Further recovery may still be required to meet regulatory limits, C) The vent hose should remain open to allow the refrigerant to be properly recovered, and D) Exceeding 90% of the drum's capacity could lead to overfilling and potential safety issues.

The correct answer is D. The vacuum pump is designed to remove refrigerant vapor from the carbon filter tank and transfer these vapors to the evaporator to minimize the loss of refrigerant to the atmosphere. This is the proper function of the vacuum pump in a centrifugal chiller high efficiency purge recovery unit, as it helps to recover and reuse the refrigerant rather than venting it to the environment. The other options are incorrect because: A) the vacuum pump is not primarily for dehydration evacuation, B) the vacuum pump does not vent non-condensable gases to the atmosphere, and C) the vacuum pump does not transfer vapors to the purge chamber to clear the float valve.

The correct answer is D) 29.99" Hg or 254 microns of Hg absolute. This is the correct answer because at a vacuum depth of 29.99" Hg or 254 microns of Hg absolute, the boiling point of moisture is the lowest, which would provide the best chance of achieving a dehydration evacuation with a deep vacuum pump. The illustrated chart shows that as the vacuum depth increases, the boiling point of moisture decreases, making it easier to remove moisture from the system. The other options, while also representing high vacuum levels, do not provide the absolute lowest boiling point of moisture compared to 29.99" Hg or 254 microns of Hg absolute.

The correct answer is B) valves "3", "4", and "6" open; valves "2", "5", "7", "8", and "10" closed. To recover the remaining R-134a refrigerant from the centrifugal chiller as a vapor, the proper valve lineup is to open the compressor suction and discharge isolation valves, as well as valves "3", "4", and "6". This allows the refrigerant vapor to be drawn into the recovery unit's compressor through the suction line, while isolating the refrigerant from the rest of the chiller system by closing valves "2", "5", "7", "8", and "10". The other answer choices are incorrect because they either do not fully isolate the refrigerant from the chiller system or do not provide the appropriate flow path for the refrigerant vapor to be drawn into the recovery unit's compressor.

The correct answer is B. The refrigerant circulating through the refrigeration system removes heat from the refrigerant through the component labeled B, which is the condenser. The condenser is responsible for removing the heat absorbed by the refrigerant in the evaporator (component A) and discharging that heat to the surrounding air or water. This is a key part of the refrigeration cycle and is necessary for the system to operate efficiently. The other options are incorrect because they do not represent the component responsible for removing heat from the refrigerant. Option A is the evaporator, which absorbs heat, option C is the receiver, and option D is the compressor, which compresses the refrigerant, but does not directly remove heat from it.

The correct answer is A) 150-190 psig. 1. Explanation: Based on the given information and the refrigeration troubleshooting guide illustration GS-RA-52, the normal range of expected discharge pressures for an air-cooled refrigerated container unit using R-134a refrigerant, operating at a box temperature set point of -15°F with a stable return air temperature of 0°F, and an ambient air temperature of 90°F, would be 150-190 psig. 2. Reasoning: The discharge pressure in a refrigeration system is primarily determined by the condensing temperature, which is affected by the ambient air temperature. With an ambient air temperature of 90°F and the unit operating in full capacity cool mode, the expected discharge pressure range would fall within 150-190 psig, as indicated in the troubleshooting guide. 3. Other options: The other options are incorrect because they do not accurately reflect the normal discharge pressure range for the given operating conditions and refrigerant.

The correct answer is A) it senses compressor suction pressure and controls the quench valve. The pressure transducer shown in the illustration GS-RA-17 is used to sense the compressor suction pressure and control the quench valve. The quench valve is responsible for regulating the flow of refrigerant into the compressor, and the pressure transducer ensures that the suction pressure is maintained within the appropriate range to prevent damage to the compressor. The other options are incorrect because they do not accurately describe the function of the pressure transducer in this specific illustration. Option B and C refer to the compressor discharge pressure, which is not the parameter being monitored by the pressure transducer in this case. Option D mentions the quench valve, but the pressure transducer is controlling it based on the compressor suction pressure, not the discharge pressure.

The correct answer is B) to the line connected to the evaporator outlet. The reasoning is that if valve "D" is a suction service valve, it would be connected to the suction side of the refrigeration system, which is the line from the evaporator outlet. This allows the suction service valve to access the low-pressure refrigerant vapor exiting the evaporator before it enters the compressor. The other options are incorrect because: A) The compressor inlet would be on the suction side, not the outlet. C) The evaporator inlet would be on the high-pressure side, not the suction side. D) The compressor outlet would be on the high-pressure side, not the suction side.

The correct answer is D) prevent the entrance of air into the chiller when the chiller is idle. The functional purpose of the illustrated LP centrifugal chiller pressure maintenance system is to prevent the entrance of air into the chiller when the chiller is not in operation. This is important to maintain the integrity of the refrigerant system and prevent air from entering the chiller, which could lead to reduced efficiency and potential damage to the equipment. The other answer choices are incorrect because: A) surging is not the purpose of this system, B) maintaining a low compression ratio is not the primary function, and C) preventing air entry is the purpose, but specifically when the chiller is idle, not under low heat load conditions.

The correct answer is C. The illustration GS-RA-12 is likely related to a navigation or radar system, and the letter C indicates the location of the receiver. This is the correct answer based on the typical layout and components of such systems, where the receiver is responsible for receiving and processing the signal. The other answer choices do not correspond to the receiver component in the illustration. A, B, and F likely represent other parts of the system, such as the antenna, display, or controls, but not specifically the receiver.

The correct answer is D) It automatically transitions the recovery unit from the direct liquid recovery mode to the direct vapor recovery mode. The functional purpose of the item labeled "FS2" in the illustrated flow diagram is to automatically switch the recovery unit from liquid recovery mode to vapor recovery mode. This is necessary to ensure the safe and efficient recovery of refrigerants from high pressure appliances, as per the EPA Clean Air Act rules. The other options are incorrect because they do not accurately describe the purpose of FS2. Option A is incorrect as FS2 does not shut down the compressor when the recovery cylinder is 80% full. Option B is incorrect as FS2 does not shut down the compressor due to excessive discharge pressure. Option C is incorrect as FS2 does not shut down the compressor based on the depth of vacuum in the refrigeration system.

The correct answer is B) Valve "14" is the king solenoid, valve "28" is the chill box solenoid, and valve "36" is the freeze box solenoid. This is the correct answer based on the information provided in the illustration GS-RA-12. The illustration labels the various valves and their functions, and option B accurately identifies the valves as described. The other options are incorrect because they do not correctly match the valves to their functions as depicted in the illustration. For example, option A incorrectly associates valve "36" with the freeze box solenoid, when the illustration shows it is the chill box solenoid. Options C and D also have inaccurate associations between the valves and their functions.

You are correct that the answer is A) cooling mode. The microprocessor-controlled temperature controller is set at -28.9°C, which is the appropriate setting for frozen cargo like ice cream. However, the actual box temperature is -18.0°C, which is warmer than the set point. In this case, the temperature controller should be in cooling mode to bring the box temperature down to the desired -28.9°C. The other options are incorrect because: B) modulating cooling mode is not necessary since the temperature is not already at the set point, C) air circulation mode would not actively cool the box, and D) heating mode would be the opposite of what is needed to cool a frozen cargo.

The correct answer is B. The 2 position diverting hot gas bypass solenoid valve would be most appropriately represented by option B in the illustration GS-RA-19. This type of valve is used to direct the refrigerant flow in a refrigeration system, allowing the hot gas to bypass the condenser coil during the defrost cycle. The solenoid valve operates in a binary fashion, either fully open or fully closed, making it suitable for this 2 position diverting application. The other options, A, C, and D, represent different types of refrigeration valves with more complex functions, such as variable metering or modulating control, which would not be the most appropriate choice for this specific application.

The correct answer is B) thermostatic expansion valve. The thermostatic expansion valve is the component where flash gas formation is a normal occurrence. As the refrigerant passes through the thermostatic expansion valve, the sudden pressure drop causes a portion of the liquid refrigerant to vaporize, creating flash gas. This flash gas formation is a normal and expected phenomenon in the operation of the thermostatic expansion valve, as it helps regulate the flow of refrigerant into the evaporator coil. The other options, A) evaporator coil, C) receiver tank, and D) condenser coil, are not the correct answers because flash gas formation is not a normal occurrence in these components of the refrigeration system.

The correct answer is D) The control bulb is located on the evaporator coil outlet. The thermostatic expansion valve regulates the flow of refrigerant into the evaporator coil based on the temperature at the evaporator outlet. The control bulb, which contains a thermostatic fluid, is placed at the evaporator outlet to sense the temperature of the refrigerant leaving the coil. This allows the thermostatic expansion valve to adjust the refrigerant flow to maintain the proper superheat and temperature in the evaporator. The other options are incorrect because: A) The thermostat, not the thermostatic expansion valve, regulates the temperature of the refrigerated space. B) The thermostatic expansion valve regulates superheat, not the solenoid valve. C) The external equalizing pipe is connected to the suction line, not the liquid receiver.

The correct answer is C) chill box thermostatic expansion valve. This is the correct answer because the valve labeled "29" in the multi-evaporator refrigeration system illustration GS-RA-12 is responsible for regulating the refrigerant flow into the chill box evaporator. The thermostatic expansion valve controls the amount of refrigerant entering the evaporator based on the temperature and pressure in the chill box, ensuring proper cooling. The other options are incorrect because they do not accurately describe the function of the specific valve labeled in the illustration. Option A refers to a pressure regulating valve, option B refers to the freeze box evaporator, and option D refers to a solenoid valve, which is a different type of refrigeration component.

The correct answer is B. The illustrated thermal expansion valve type B would be the most appropriate choice for an evaporator coil with a 2 psi pressure drop, as it provides externally adjustable superheat and a replaceable power element, which are both desired features in this application. The other options would not be as suitable - type A lacks external superheat adjustment, type C does not have a replaceable power element, and type D is typically used for higher pressure drop applications.

The correct answer is C. The expansion valve designed to maintain a constant evaporator pressure rather than a constant evaporator superheat is the thermostatic expansion valve (TXV), which is represented by option C in the illustration. The TXV is designed to maintain a constant pressure in the evaporator by automatically adjusting the refrigerant flow based on changes in the evaporator load, which helps to optimize the system's performance. The other options, A, B, and D, represent different types of expansion valves that are designed to maintain a constant evaporator superheat rather than a constant evaporator pressure.

The correct answer is A) compressor. The compressor is the component in a refrigeration system labeled "A" in the illustration GS-RA-12. The compressor is the heart of the refrigeration cycle, as it circulates the refrigerant and provides the necessary pressure and temperature changes to enable the cooling process. The other options are incorrect because: B) the condenser is the component that condenses the refrigerant from a gas to a liquid, C) the accumulator collects any excess refrigerant in the system, and D) the filter drier removes any contaminants from the refrigerant.

The correct answer is B) welded, fully hermetic. The illustration GS-RA-41 likely depicts a refrigeration compressor arrangement. In a fully hermetic compressor, the compressor and motor are enclosed in a welded steel shell, creating a completely sealed unit. This design is more efficient and reliable than an open or semi-hermetic arrangement, as it prevents any potential leaks. The fully hermetic, welded construction makes this type of compressor well-suited for the maritime environment and the requirements of the US Coast Guard Captain's License Examinations. The other options are incorrect because: A) external-drive compressors have the motor separate from the compressor; C) open compressors have an exposed design that is less suitable for marine applications; and D) semi-hermetic compressors, while more accessible for service, do not provide the same leak-proof integrity as a fully hermetic design.

The correct answer is C) 70 degrees F. The dew point temperature of air at 80 degrees F and 70% relative humidity is 70 degrees F. This can be determined using a psychrometric chart or calculated using the appropriate formula. The air conditioning process does not change the dew point temperature, so the resulting dew point temperature of the conditioned air just before it contacts the cooling coil will also be 70 degrees F. The other options are incorrect because they do not represent the dew point temperature of the given air conditions. A) 64 degrees F, B) 67 degrees F, and D) 73 degrees F are not the correct dew point temperature for the specified air conditions.

The correct answer is C: The dry bulb room temperature is controlled by a steam heated reheater and its associated pneumatic control valve. This is correct because in a Class "A" air conditioning system used to condition large public spaces, the dry bulb temperature of the space is controlled by a steam heated reheater. The reheater, and its associated control valve, are used to reheat the air after it has passed through the cooling coil, allowing precise temperature control of the space. The other options are incorrect - A is incorrect because the preheater steam flow is typically controlled by a separate thermostat, not the space thermostat. B is incorrect because the cooling coil and reheater can be used simultaneously to provide precise temperature control. D is incorrect because the reheater is used even when in the cooling mode, to provide the final temperature adjustment.

The correct answer is A) The duct thermostat determines the amount of water flow circulating through the cooling coil. In a class "D" air conditioning system, the duct thermostat monitors the temperature of the air flowing through the ductwork and controls the amount of water circulating through the cooling coil. This adjusts the cooling capacity of the system to maintain the desired temperature in the conditioned space. The other options are incorrect because: B) The cooling is achieved through the refrigerant circuit, not a direct type air conditioning unit. C) Increasing recirculated air would increase the heat load, not decrease it. D) The room thermostat controls the dry bulb temperature, not the wet bulb temperature, of the conditioned space.

The correct answer is B. When recovering refrigerant from a centrifugal chiller using the method shown in the illustration GS-RA-59, it is possible to achieve the recovery levels required by law without any further recovery. This is because the illustration depicts a closed-loop recovery system, where the refrigerant is recovered as a vapor and contained in a dedicated recovery tank. This allows for the complete removal of the refrigerant charge from the chiller, meeting the regulatory requirements for refrigerant recovery. The other options are incorrect: A) The entire charge may not be removed in one procedure, as the recovery process may need to be performed in multiple stages to ensure complete removal of the refrigerant. C) The containment tank should not be vented back to the chiller evaporator shell, as this would compromise the closed-loop recovery system and potentially release refrigerant to the atmosphere. D) The refrigerant is being recovered as a vapor, not a liquid, as indicated by the closed-loop recovery system design.

The correct answer is C) 40 grains. To determine the quantity of moisture removed from one pound of the conditioned air, we need to use the psychrometric chart. The psychrometric chart shows the relationship between temperature, relative humidity, and the amount of moisture in the air. Given: - The introduction of outside air is 90°F with a relative humidity of 60%. - The air has been conditioned to 70°F with a relative humidity of 80%. By locating the two points on the psychrometric chart and drawing a line between them, we can determine the difference in moisture content, which is 40 grains per pound of air. The other options are incorrect because they do not match the value obtained from the psychrometric chart analysis.

The correct answer is A) The expansion valve would hunt excessively, alternately starving and over feeding the evaporator coil. If the replacement valve cage is oversized at 5 tons compared to the original 1/2 ton rating, the expansion valve will not be able to properly regulate the flow of refrigerant to the evaporator coil. The oversized valve cage will cause the expansion valve to "hunt" or cycle excessively, resulting in alternating periods of starving and over-feeding the evaporator coil. This hunting behavior will lead to inconsistent superheat and poor performance of the refrigeration system. The other answer choices are incorrect because: B) is incorrect as the oversized valve cage would cause problems, C) and D) are incorrect as the evaporator would experience both starvation and over-feeding, not just one or the other.

The correct answer is D. The method used to determine the amount of superheat present in the suction gas leaving the evaporator coil is to note the low side pressure, determine the corresponding saturation temperature, and subtract it from the temperature measured with a thermometer at the thermostatic expansion valve sensing bulb. This is because the difference between the saturation temperature and the actual temperature of the suction gas is the amount of superheat. The other options are incorrect because they do not correctly describe the method for determining superheat. Option A measures the temperature at the compressor suction inlet instead of the thermostatic expansion valve sensing bulb, and option B subtracts the wrong temperature. Option C adds the saturation temperature instead of subtracting it.

The correct answer is C) The expansion valve should not be adjusted, as the degree of superheat is within the accepted range. This is the correct answer because the low side pressure of 15 psig and the coil temperature of 10°F indicates that the system is operating with a proper degree of superheat, which is typically between 6-12°F. Adjusting the expansion valve is not necessary, as the system is functioning within the acceptable parameters. The other options are incorrect because they suggest issues that are not indicated by the given information. Cleaning the evaporator coils or changing the filter drier are not necessary based on the provided data, and the liquid line strainer does not need to be cleaned if the system is operating properly.

The correct answer is C. The illustration GS-RA-50 shows the proper method for attaching a TXV feeler bulb to a large line (7/8" and larger) with a horizontal run. Option C depicts the correct technique, which involves securing the feeler bulb to the side of the horizontal line using a clamp or strap. This ensures proper heat transfer from the line to the feeler bulb, allowing the thermostatic expansion valve (TXV) to accurately sense the refrigerant temperature and adjust the flow accordingly. The other options, A, B, and D, depict less suitable methods that may not provide sufficient contact between the feeler bulb and the refrigerant line, potentially leading to inaccurate temperature sensing and improper TXV operation.