Download Refrigeration Operating Engineer License Ultimate Exam and more Exams Technology in PDF only on Docsity!
Engineer License Ultimate
Exam
Question 1. Which law states that energy cannot be created or destroyed, only transferred? A) First Law of Thermodynamics B) Second Law of Thermodynamics C) Third Law of Thermodynamics D) Law of Conservation of Mass Answer: A Explanation: The First Law of Thermodynamics is the principle of energy conservation, applicable to refrigeration cycles. Question 2. In a refrigeration system, the term “sensible heat” refers to: A) Heat absorbed during a phase change B) Heat that changes the temperature of a fluid without a phase change C) Heat removed by the condenser D) Heat generated by the compressor Answer: B Explanation: Sensible heat changes temperature only; latent heat involves phase changes such as vaporization. Question 3. A refrigerant with an ODP of 0 and a GWP of less than 10 is classified as: A) CFC B) HCFC
Engineer License Ultimate
Exam
C) HFC
D) Natural refrigerant Answer: C Explanation: Hydrofluorocarbons (HFCs) have zero ozone depletion potential and relatively low global warming potential compared to many alternatives. Question 4. The pressure-temperature (P-T) relationship for a refrigerant is primarily used to: A) Determine oil viscosity B) Locate the refrigerant on a P-H chart C) Calculate compressor displacement D) Select the correct fan size Answer: B Explanation: The P-T curve lets technicians read the corresponding temperature for a given pressure, essential for chart plotting. Question 5. Which component controls the amount of refrigerant entering the evaporator in a DX system? A) Condenser fan B) Compressor C) Thermostatic expansion valve (TXV) D) Suction line accumulator Answer: C
Engineer License Ultimate
Exam
A) Excess oil in the suction line B) Liquid refrigerant entering the compressor C) Over-charging of refrigerant in the condenser D) A sudden rise in discharge pressure Answer: B Explanation: Slugging occurs when liquid refrigerant reaches the compressor, causing mechanical damage. Question 9. A high-pressure cut-out switch is typically set to protect against: A) Low suction pressure B) Oil starvation C) Overheating of the compressor discharge line D) Excessive superheat in the evaporator Answer: C Explanation: The high-pressure cut-out opens when discharge pressure exceeds safe limits, preventing component rupture. Question 10. Which refrigerant classification indicates a mildly flammable, low-toxicity refrigerant? A) A B) A2L C) B D) C
Engineer License Ultimate
Exam
Answer: B Explanation: “A2L” denotes low-toxicity, mildly flammable refrigerants per ASHRAE safety groups. Question 11. The coefficient of performance (COP) of a refrigeration system is defined as: A) Refrigeration effect ÷ Compressor work input B) Compressor work ÷ Refrigeration effect C) Heat rejected ÷ Heat absorbed D) Evaporator temperature ÷ Condenser temperature Answer: A Explanation: COP = Q_L / W, where Q_L is the cooling load (refrigeration effect) and W is the compressor work. Question 12. In a brine secondary system, the purpose of the glycol is to: A) Increase the boiling point of the water B) Prevent corrosion in the evaporator C) Lower the freezing point of the secondary fluid D) Act as a refrigerant in the primary loop Answer: C Explanation: Glycol depresses the freezing point, allowing the brine to operate below 0 °C without freezing.
Engineer License Ultimate
Exam
C) 200 % of design pressure D) 110 % of design pressure Answer: B Explanation: ASHRAE and UL standards generally require relief devices set at 125 % of the maximum allowable working pressure. Question 16. In an absorption refrigeration system using ammonia-water, the absorber’s primary role is to: A) Condense vapor refrigerant B) Evaporate the refrigerant C) Dissolve ammonia into water, releasing heat D) Separate oil from refrigerant Answer: C Explanation: The absorber absorbs ammonia vapor into water, producing a solution and rejecting heat. Question 17. Which of the following oil types is compatible with HFC-134a? A) Mineral oil B) Polyolester (POE) oil C) Polyalkylene glycol (PAG) oil D) Silicone oil Answer: B
Engineer License Ultimate
Exam
Explanation: POE oils are formulated for use with HFC-134a and other HFC refrigerants. Question 18. A suction line accumulator is installed primarily to: A) Increase refrigerant mass flow B) Remove non-condensable gases C) Capture liquid refrigerant that may return to the compressor D) Provide a location for oil return Answer: C Explanation: Accumulators hold excess liquid, preventing it from entering the compressor. Question 19. The term “superheated vapor” means: A) Vapor at a temperature below its saturation point B) Vapor at a temperature above its saturation point C) Vapor mixed with liquid droplets D) Vapor with dissolved oil Answer: B Explanation: Superheated vapor has a temperature higher than the saturation temperature at the same pressure. Question 20. Which control device measures the temperature of the air entering the evaporator and modulates compressor speed accordingly?
Engineer License Ultimate
Exam
Explanation: Flooded evaporators maintain a liquid pool over the coil, ensuring full surface wetting. Question 23. The primary advantage of a scroll compressor over a reciprocating compressor is: A) Higher displacement volume B) Fewer moving parts and lower vibration C) Ability to handle high-pressure refrigerants only D) Lower cost of manufacture Answer: B Explanation: Scroll compressors have fewer moving parts, resulting in smoother operation and less vibration. Question 24. Which of the following is NOT a typical symptom of a refrigerant leak? A) Decrease in suction pressure B) Increase in discharge temperature C) Rise in oil temperature in the compressor D) Sudden increase in evaporator superheat Answer: C Explanation: Oil temperature may not change significantly; the other options directly reflect leak effects. Question 25. The correct order of components in a standard vapor-compression cycle is:
Engineer License Ultimate
Exam
A) Compressor → Condenser → Expansion device → Evaporator B) Evaporator → Compressor → Condenser → Expansion device C) Condenser → Compressor → Evaporator → Expansion device D) Expansion device → Compressor → Condenser → Evaporator Answer: A Explanation: The cycle proceeds from low-pressure vapor (compressor) to high-pressure condensation, expansion, and evaporation. Question 26. Which type of cooling tower water treatment chemical is used to prevent microbial growth? A) Scale inhibitor B) Biocide C) Corrosion inhibitor D) pH adjuster Answer: B Explanation: Biocides are added to control bacteria, algae, and fungi in cooling tower water. Question 27. The term “subcooled liquid” refers to a refrigerant that is: A) At its saturation temperature B) Below its saturation temperature while still liquid C) Above its saturation temperature while liquid
Engineer License Ultimate
Exam
Question 30. During a hot-gas defrost, the valve arrangement typically: A) Directs high-pressure gas from the compressor discharge to the evaporator coil B) Bypasses the condenser and sends low-pressure gas to the evaporator C) Opens the suction line accumulator to release gas into the evaporator D) Routes liquid refrigerant from the condenser to the evaporator Answer: A Explanation: Hot-gas defrost uses discharge gas to melt frost on the evaporator, temporarily stopping cooling. Question 31. The primary purpose of a sight glass on a refrigeration system is to: A) Measure discharge pressure B) Indicate oil level in the compressor C) Detect the presence of liquid refrigerant in the suction line D) Monitor condenser temperature Answer: C Explanation: A sight glass allows visual detection of liquid droplets in the suction line, indicating potential slugging.
Engineer License Ultimate
Exam
Question 32. Which of the following best describes a “low-temperature” (LT) refrigerant? A) Operates above 250 °F at saturation B. Has a boiling point below 0 °C at atmospheric pressure C) Is classified as A1 safety group D) Is non-flammable with high GWP Answer: B Explanation: Low-temperature refrigerants have low boiling points, enabling operation well below freezing. Question 33. The term “COP” for a heat pump providing heating is calculated as: A) Heat delivered ÷ Compressor work B) Cooling load ÷ Compressor work C) Refrigeration effect ÷ Heat rejected D) Discharge temperature ÷ Suction temperature Answer: A Explanation: For heating mode, COP = Q_H / W, where Q_H is heat delivered to the space. Question 34. In a centrifugal chiller, the “head” of the pump is most directly related to: A) Compressor speed B) Refrigerant mass flow rate
Engineer License Ultimate
Exam
Explanation: Air (primarily nitrogen and oxygen) does not condense at typical system pressures and temperatures, causing performance loss. Question 37. Which type of expansion device provides a constant pressure drop regardless of load conditions? A) Thermostatic expansion valve (TXV) B) Automatic expansion valve (AXV) C) Capillary tube D) Electronic expansion valve (EEV) Answer: C Explanation: A capillary tube’s restriction creates a fixed pressure drop that does not adjust to load changes. Question 38. The primary function of a VFD (Variable Frequency Drive) in a refrigeration plant is to: A) Increase system pressure B) Control motor speed to match load demand C) Provide overload protection for compressors D) Convert AC to DC power Answer: B Explanation: VFDs vary motor frequency, thereby adjusting compressor speed and capacity to meet cooling loads efficiently.
Engineer License Ultimate
Exam
Question 39. In a liquid-overfeed evaporator, the refrigerant is supplied as: A) A subcooled liquid that overfills the coil, then flashes to vapor B) A superheated vapor from the TXV C) A mixture of vapor and liquid from the accumulator D) Saturated liquid directly from the condenser Answer: A Explanation: Overfeed evaporators intentionally deliver excess liquid, which flashes to vapor, providing high heat transfer rates. Question 40. The most common reason for a “short-cycling” condition in a chilled water plant is: A) Oversized compressor capacity relative to load B) Low condenser water flow C) High suction pressure cut-out set too low D) Faulty high-pressure relief valve Answer: A Explanation: An oversized compressor reaches setpoint quickly, then shuts off, causing frequent cycles. Question 41. Which of the following statements about the “critical point” of a refrigerant is correct? A) It is the temperature at which the refrigerant changes from liquid to solid
Engineer License Ultimate
Exam
Explanation: The generator uses an external heat source (steam or hot water) to boil ammonia out of the solution. Question 44. The term “superheat” is measured at which point in the refrigeration cycle? A) At the condenser outlet B) At the evaporator inlet (suction line) C) At the compressor inlet D) At the expansion valve outlet Answer: B Explanation: Superheat is the temperature rise of vapor above its saturation temperature at the evaporator outlet. Question 45. Which of the following is a requirement of ASHRAE 15 for a commercial refrigeration system? A) Minimum of three fire sprinklers per floor B) Use of only non-flammable refrigerants C) Installation of a pressure relief device set at 125 % of design pressure D) Mandatory weekly leak testing with a halogen detector Answer: C Explanation: ASHRAE 15 mandates pressure relief devices sized and set per the 125 % rule.
Engineer License Ultimate
Exam
Question 46. The most accurate method to determine the amount of refrigerant required to charge a system is: A) Measuring the length of suction line B) Using the system’s rated capacity and refrigerant density at operating temperature C) Filling the condenser until the pressure gauge reads 150 psi D) Guessing based on previous similar installations Answer: B Explanation: Calculating charge based on capacity and refrigerant density at the intended operating temperature yields the correct mass. Question 47. When performing a leak test with an electronic leak detector, the device is most sensitive to which refrigerant characteristic? A) Color of the gas B) Molecular weight C) Fluorine content D) Vapor pressure at ambient temperature Answer: D Explanation: Leak detectors respond to the vapor pressure (concentration) of the refrigerant in the air. Question 48. In a centrifugal chiller, the “NPSH” (Net Positive Suction Head) is important because:
