Exam 1

Question 1

Q1. The efficiency of the refrigerant cycle is affected by the operation of the condenser. A more efficient centrifugal compressor operation results from:

A. Raising the condenser liquid level to the maximum
B. Lowering the chilled-water set point
C. Raising the condenser head pressure
D. Lowering the condensing pressure

Answer 1

✅ D. Lowering the condensing pressure

💡 Explanation:
Lowering the condensing pressure reduces the compressor’s compression ratio and the work required to move refrigerant through the cycle.

📘 Key Concept:
Compressor efficiency improves when condensing temperature and pressure are minimized.

Question 2

Q2. The heat removed from the refrigerant in a condenser is:

A. Sensible and latent heat
B. Latent heat only
C. Radiant heat only
D. Sensible heat only

Answer 2

✅ A. Sensible and latent heat

💡 Explanation:
The condenser removes both sensible and latent heat as the refrigerant desuperheats and condenses.

📘 Key Concept:
Condensers reject both heat of condensation and desuperheating to complete the refrigeration cycle.

Question 3

Q3. When withdrawing refrigerant for storage during major repairs, the NYC Fire Code requires that the storage containers:

A. Do not weigh more than 200 pounds when filled
B. Are approved by the U.S. Department of Transportation
C. Are approved by the OSHA Association
D. Do not exceed 55 gallons in capacity

Answer 3

✅ B. Are approved by the U.S. Department of Transportation

💡 Explanation:
DOT approval ensures the cylinders meet pressure and safety standards.

📘 Key Concept:
Cylinders must show DOT markings (e.g., DOT-4BA400) and undergo hydrostatic testing every 5 years.

Question 4

Q4. Which of the following best describes how a cylinder unloader works?

A. Keeps the suction valve open while the compressor is in the return stroke
B. Controls the clearance volume in the compressor with a solenoid
C. Controls the opening of the passage into the compressor with variable vanes
D. Unloads the piston to create less pressure

Answer 4

✅ A. Keeps the suction valve open while the compressor is in the return stroke

💡 Explanation:
This method prevents compression in selected cylinders, reducing capacity and saving energy.

📘 Key Concept:
Unloaders allow part-load operation without shutting the compressor off.

Question 5

Q5. In most semi-hermetic compressors, the suction vapor is used to:

A. Remove oil from the motor housing
B. Cool the motor
C. Minimize oil foaming
D. Remove oil foam from the shaft

Answer 5

✅ B. Cool the motor

💡 Explanation:
Suction vapor passes over motor windings to remove heat and prevent overheating.

📘 Key Concept:
Maintains motor temperature using refrigerant gas for cooling.

Question 6

Q6. The amount of refrigerant that flows through the orifices of an economizer is determined by the:

A. Number of economizer stages
B. Temperature of the high-side refrigerant
C. Number of compressor stages
D. Difference between the high-side and low-side pressures

Answer 6

✅ D. Difference between the high-side and low-side pressures

💡 Explanation:
The pressure differential across the economizer orifice drives refrigerant flow.

📘 Key Concept:
Mass flow through the economizer is proportional to the square root of the pressure difference.

Question 7

Q7. An in-line refrigerant cleaning system is advisable:

A. For high-pressure refrigerant systems
B. To purge non-condensables
C. For systems using toxic refrigerants
D. To remove impurities from the system

Answer 7

✅ D. To remove impurities from the system

💡 Explanation:
In-line cleaning removes acids, sludge, and debris circulating with refrigerant.

📘 Key Concept:
Common after compressor burnouts to prevent system contamination.

Question 8

Q8. The type of refrigerant system least likely to leak refrigerant into building spaces being cooled is:

A. The direct-vented closed system
B. The direct closed system
C. Any system using a reciprocating compressor
D. The indirect system

Answer 8

✅ D. The indirect system

💡 Explanation:
Indirect systems use a secondary coolant loop, isolating refrigerant from occupied areas.

📘 Key Concept:
Improves safety for large buildings and toxic refrigerants like ammonia.

Question 9

Q9. The suction pressure of a reciprocating compressor is 65 psig, and the discharge pressure is 120 psig. Atmospheric pressure is 14.7 psi. The compression ratio is closest to:

A. 2.07
B. 4.41
C. 1.69
D. 1.84

Answer 9

✅ A. 2.07

💡 Explanation:
Convert to absolute pressures: 134.7 psia ÷ 79.7 psia = 2.07.

📘 Key Concept:
Compression Ratio = (Discharge + 14.7) ÷ (Suction + 14.7).

Question 10

Q10. A superheated vapor is:

A. A dry vapor at the saturation temperature
B. A dry saturated vapor
C. A dry vapor above the saturation temperature
D. Vapor with a minimal amount of included liquid

Answer 10

✅ C. A dry vapor above the saturation temperature

💡 Explanation:
Superheating means adding heat beyond saturation to ensure no liquid remains.

📘 Key Concept:
Superheat = Actual suction temperature − Saturation temperature (8–12°F typical).

Question 11

Q11. The component that prevents liquid refrigerant from entering the compressor is the:

A. Expansion valve
B. Accumulator
C. Receiver
D. Solenoid valve

Answer 11

✅ B. Accumulator

💡 Explanation:
An accumulator collects liquid refrigerant returning from the evaporator, allowing only vapor to enter the compressor.

📘 Key Concept:
Prevents compressor damage caused by liquid slugging and ensures vapor-only suction flow.

Question 12

Q12. The pressure at which a low-pressure cutout control stops the compressor is called:

A. Differential pressure
B. Cut-in pressure
C. Cut-out pressure
D. Static pressure

Answer 12

✅ C. Cut-out pressure

💡 Explanation:
The low-pressure control shuts off the compressor when suction pressure falls to a set cut-out point.

📘 Key Concept:
Protects the compressor from operating at dangerously low suction pressures.

Question 13

Q13. A thermostatic expansion valve controls the refrigerant flow according to the:

A. Evaporator pressure
B. Evaporator superheat
C. Condenser temperature
D. Suction pressure

Answer 13

✅ B. Evaporator superheat

💡 Explanation:
The TXV modulates refrigerant flow to maintain a constant superheat at the evaporator outlet.

📘 Key Concept:
Maintains efficient heat transfer and prevents liquid refrigerant from reaching the compressor.

Question 14

Q14. If the water-cooled condenser tubes become fouled, the condenser pressure will:

A. Increase
B. Decrease
C. Remain the same
D. Fluctuate rapidly

Answer 14

✅ A. Increase

💡 Explanation:
Fouling restricts heat transfer, causing higher head pressure and compressor workload.

📘 Key Concept:
Regular tube cleaning and chemical treatment prevent high condensing pressure and energy waste.

Question 15

Q15. The purpose of a liquid receiver in a refrigeration system is to:

A. Store liquid refrigerant
B. Prevent compressor flooding
C. Control refrigerant flow
D. Collect oil and moisture

Answer 15

✅ A. Store liquid refrigerant

💡 Explanation:
The receiver holds excess liquid refrigerant, ensuring a steady liquid supply to the expansion device.

📘 Key Concept:
Located after the condenser, it provides storage and surge capacity during varying loads.

Question 16

Q16. The pressure difference between the discharge and suction side of a pump is known as:

A. Velocity head
B. Total dynamic head
C. Static head
D. Friction loss

Answer 16

✅ B. Total dynamic head

💡 Explanation:
It represents the energy needed to move fluid from suction to discharge, including static and friction losses.

📘 Key Concept:
TDH = Static Head + Friction Head + Velocity Head.

Question 17

Q17. In a centrifugal pump, cavitation is caused by:

A. Excessive discharge pressure
B. Low suction pressure
C. High flow velocity
D. Excessive water temperature

Answer 17

✅ B. Low suction pressure

💡 Explanation:
When suction pressure drops below vapor pressure, vapor bubbles form and collapse, damaging impeller surfaces.

📘 Key Concept:
Maintain proper Net Positive Suction Head (NPSH) to avoid cavitation.

Question 18

Q18. The device used to prevent backflow of refrigerant into the condenser is the:

A. Solenoid valve
B. Check valve
C. Expansion valve
D. Receiver

Answer 18

✅ B. Check valve

💡 Explanation:
A check valve allows flow in one direction only, preventing reverse refrigerant movement.

📘 Key Concept:
Protects system components during shutdown and compressor reversal.

Question 19

Q19. In a refrigeration system, the expansion valve maintains a constant:

A. Temperature difference between inlet and outlet
B. Evaporator pressure
C. Amount of refrigerant charge
D. Degree of superheat

Answer 19

✅ D. Degree of superheat

💡 Explanation:
The valve adjusts refrigerant flow so that vapor leaving the evaporator is slightly superheated.

📘 Key Concept:
Ensures proper evaporation and prevents liquid refrigerant return.

Question 20

Q20. The condenser in a refrigeration system is located between the:

A. Evaporator and receiver
B. Compressor and expansion valve
C. Receiver and evaporator
D. Compressor and evaporator

Answer 20

✅ B. Compressor and expansion valve

💡 Explanation:
Hot discharge gas from the compressor enters the condenser, where it rejects heat and condenses to liquid before expansion.

📘 Key Concept:
Condenser rejects heat to air or water, completing the high-pressure side of the cycle.

Question 21

Q21. Which of the following instruments is used to measure the superheat of a refrigerant vapor?

A. Pressure gauge
B. Thermometer
C. Manifold gauge set and thermometer
D. Psychrometer

Answer 21

✅ C. Manifold gauge set and thermometer

💡 Explanation:
To determine superheat, measure suction pressure with a manifold gauge, convert it to saturation temperature, then subtract that from the actual suction-line temperature measured with a thermometer.

📘 Key Concept:
Superheat = Actual Suction Temperature − Saturation Temperature (from pressure chart).

Question 22

Q22. A high condensing pressure in a refrigeration system is often caused by:

A. Low ambient temperature
B. Dirty condenser coils
C. Low refrigerant charge
D. Excessive evaporator load

Answer 22

✅ B. Dirty condenser coils

💡 Explanation:
Fouled coils restrict heat transfer, raising condensing temperature and head pressure.

📘 Key Concept:
Regular condenser cleaning maintains efficiency and prevents compressor overload.

Question 23

Q23. The purpose of an oil separator in a refrigeration system is to:

A. Collect excess refrigerant
B. Remove moisture from oil
C. Return oil to the compressor crankcase
D. Prevent oil foaming

Answer 23

✅ C. Return oil to the compressor crankcase

💡 Explanation:
The oil separator removes oil from discharge gas and returns it to the compressor via a float valve or small line.

📘 Key Concept:
Prevents oil starvation in compressor and improves evaporator performance.

Question 24

Q24. When a pump operates against a closed discharge valve, the pump is:

A. Cavitating
B. Deadheaded
C. Air-bound
D. Primed

Answer 24

✅ B. Deadheaded

💡 Explanation:
Running a pump with no discharge path causes rapid pressure rise and heat buildup, which can damage seals and impellers.

📘 Key Concept:
Always open discharge valve before starting pump to ensure flow and cooling.

Question 25

Q25. The primary purpose of a sight glass in a liquid refrigerant line is to: A. Measure flow velocity B. Indicate moisture and refrigerant condition C. Control pressure drop D. Prevent refrigerant flashing

Answer 25

✅ B. Indicate moisture and refrigerant condition 💡 Explanation: A sight glass shows refrigerant flow and includes a moisture indicator that changes color if moisture is present. 📘 Key Concept: Green = Dry; Yellow = Moist; Bubbles = Possible low charge or flashing.

Question 26

Q26. What happens if air or non-condensables are present in a refrigeration system? A. Head pressure increases B. Evaporator temperature decreases C. Compressor efficiency improves D. Condenser pressure decreases

Answer 26

✅ A. Head pressure increases 💡 Explanation: Air and non-condensables occupy space in the condenser, reducing effective heat-transfer area and raising condensing pressure. 📘 Key Concept: Purge non-condensables from high-pressure side to maintain proper efficiency.

Question 27

Q27. The purpose of an evaporator in a refrigeration system is to: A. Absorb heat into the refrigerant B. Reject heat from the refrigerant C. Convert liquid refrigerant to vapor in the condenser D. Raise discharge pressure

Answer 27

✅ A. Absorb heat into the refrigerant 💡 Explanation: The evaporator transfers heat from air or water into the refrigerant, causing it to evaporate into vapor. 📘 Key Concept: Evaporators operate at low pressure and temperature to absorb latent heat from the medium being cooled.

Question 28

Q28. If a refrigeration system is overcharged with refrigerant, the most likely symptom is: A. Low suction pressure B. High head pressure C. Frost on the suction line D. Low discharge temperature

Answer 28

✅ B. High head pressure 💡 Explanation: Excess refrigerant overfills the condenser, reducing space for vapor and raising condensing pressure. 📘 Key Concept: Proper charge ensures correct subcooling and efficient operation.

Question 29

Q29. The most accurate way to determine a refrigerant leak is by: A. Soap bubble test B. Electronic leak detector C. Halide torch D. Visual frost inspection

Answer 29

✅ B. Electronic leak detector 💡 Explanation: Electronic detectors sense minute concentrations of refrigerant gas faster and more accurately than other methods. 📘 Key Concept: Leak testing ensures safety and compliance with EPA refrigerant-handling rules.

Question 30

Q30. In a refrigeration system, subcooling is measured: A. At the evaporator outlet B. In the compressor suction line C. At the condenser outlet D. In the liquid line before expansion valve

Answer 30

✅ D. In the liquid line before expansion valve 💡 Explanation: Subcooling is the temperature difference between saturated liquid temperature and actual liquid-line temperature at the condenser outlet. 📘 Key Concept: Typical subcooling: 8–12°F; ensures liquid refrigerant reaches the expansion valve without flashing.

Question 31

Q31. The main purpose of an evaporator pressure regulator (EPR) valve is to: A. Maintain a constant suction pressure B. Maintain a minimum evaporator pressure C. Prevent compressor short-cycling D. Reduce discharge pressure

Answer 31

✅ B. Maintain a minimum evaporator pressure 💡 Explanation: An EPR valve holds back refrigerant leaving the evaporator to maintain pressure above a set minimum, preventing coil freezing and controlling temperature. 📘 Key Concept: Used in multi-evaporator systems to keep each evaporator at its desired pressure and temperature.

Question 32

Q32. The main function of the compressor in a refrigeration system is to: A. Absorb heat B. Remove moisture from refrigerant C. Circulate refrigerant and raise its pressure D. Condense refrigerant vapor

Answer 32

✅ C. Circulate refrigerant and raise its pressure 💡 Explanation: The compressor pumps refrigerant vapor from low-pressure evaporator to high-pressure condenser, enabling the refrigerant to reject heat. 📘 Key Concept: Converts low-pressure vapor to high-pressure vapor; often called the 'heart' of the system.

Question 33

Q33. A flooded evaporator differs from a dry-type evaporator because it: A. Contains refrigerant vapor only B. Has refrigerant covering all tubes C. Uses a capillary tube for metering D. Operates under vacuum only

Answer 33

✅ B. Has refrigerant covering all tubes 💡 Explanation: In flooded evaporators, liquid refrigerant fills the evaporator tubes to improve heat transfer. A float valve maintains proper liquid level. 📘 Key Concept: Common in large systems with surge drums to ensure efficient heat exchange.

Question 34

Q34. The substance used to neutralize acid in a refrigeration system is: A. Alcohol B. Potassium hydroxide C. Activated alumina D. Molecular sieve

Answer 34

✅ C. Activated alumina 💡 Explanation: Activated alumina absorbs moisture and neutralizes acids formed by refrigerant and oil breakdown. 📘 Key Concept: Often found in filter-driers to protect compressor and system from corrosion.

Question 35

Q35. In a water-cooled condenser, scale buildup on tube walls will: A. Increase heat transfer B. Decrease condensing pressure C. Decrease heat transfer efficiency D. Have no effect

Answer 35

✅ C. Decrease heat transfer efficiency 💡 Explanation: Scale acts as insulation, reducing heat transfer and causing higher head pressure and energy consumption. 📘 Key Concept: Regular chemical treatment and descaling prevent efficiency loss.

Question 36

Q36. The most likely cause of frost on a suction line is: A. Excess refrigerant charge B. Low evaporator airflow C. High head pressure D. Overheated compressor

Answer 36

✅ B. Low evaporator airflow 💡 Explanation: Restricted airflow prevents proper heat absorption, causing the coil and suction line to drop below freezing. 📘 Key Concept: Check for dirty filters, fan failure, or iced coils.

Question 37

Q37. The oil pressure safety switch on a compressor is designed to: A. Shut down the compressor when oil pressure drops too low B. Regulate oil temperature C. Maintain crankcase pressure D. Prevent oil foaming

Answer 37

✅ A. Shut down the compressor when oil pressure drops too low 💡 Explanation: Low oil pressure protection prevents bearing and crankshaft damage from inadequate lubrication. 📘 Key Concept: Safety switches often have a time delay to allow normal pressure buildup on startup.

Question 38

Q38. What happens when the thermostatic expansion valve sensing bulb loses its charge? A. Valve remains fully open B. Valve remains closed C. Suction pressure rises rapidly D. Evaporator floods

Answer 38

✅ B. Valve remains closed 💡 Explanation: Without bulb pressure, the valve’s diaphragm cannot open, starving the evaporator of refrigerant. 📘 Key Concept: Always mount bulbs securely and check for insulation damage or leaks.

Question 39

Q39. The pressure relief valve on a refrigeration system is designed to: A. Protect the compressor from high discharge temperature B. Protect the system from excessive pressure C. Prevent liquid slugging D. Maintain constant suction pressure

Answer 39

✅ B. Protect the system from excessive pressure 💡 Explanation: Pressure relief valves automatically vent refrigerant gas when system pressure exceeds design limits. 📘 Key Concept: Usually set to open at 10% above maximum allowable working pressure (MAWP).

Question 40

Q40. A decrease in suction pressure and an increase in superheat usually indicate: A. Low refrigerant charge B. Dirty condenser C. Flooded evaporator D. Restricted discharge line

Answer 40

✅ A. Low refrigerant charge 💡 Explanation: Low charge reduces refrigerant flow, lowering suction pressure and raising superheat due to reduced cooling load. 📘 Key Concept: Check for leaks and correct charge to restore normal pressures and temperatures.

Question 41

Q41. Which of the following indicates an overfed evaporator? A. High suction pressure and low superheat B. Low suction pressure and high superheat C. Low head pressure and normal superheat D. High head pressure and low subcooling

Answer 41

✅ A. High suction pressure and low superheat 💡 Explanation: Too much refrigerant entering the evaporator causes excessive liquid presence, resulting in high suction pressure and very little superheating. 📘 Key Concept: An overfed evaporator can flood the compressor with liquid; adjust expansion valve or reduce charge.

Question 42

Q42. The discharge gas from a refrigeration compressor is: A. Superheated vapor B. Saturated vapor C. Subcooled liquid D. Two-phase mixture

Answer 42

✅ A. Superheated vapor 💡 Explanation: Compressor discharge gas is always superheated due to the heat of compression. 📘 Key Concept: Superheat ensures refrigerant remains vapor as it enters the condenser.

Question 43

Q43. The type of heat absorbed by the refrigerant in the evaporator is: A. Latent heat B. Sensible heat C. Radiant heat D. Convective heat

Answer 43

✅ A. Latent heat 💡 Explanation: The refrigerant absorbs latent heat from the medium being cooled, changing from liquid to vapor. 📘 Key Concept: Latent heat transfer occurs during phase change without temperature increase.

Question 44

Q44. A thermostatic expansion valve with too little superheat adjustment will cause: A. Starving of the evaporator B. Flooding of the evaporator C. High discharge temperature D. Low suction pressure

Answer 44

✅ B. Flooding of the evaporator 💡 Explanation: If superheat is set too low, the valve overfeeds refrigerant, causing liquid to leave the evaporator. 📘 Key Concept: Proper superheat adjustment ensures only vapor returns to compressor.

Question 45

Q45. The primary function of a liquid line filter-drier is to: A. Absorb moisture and acids B. Remove oil from refrigerant C. Reduce pressure drop D. Separate vapor from liquid

Answer 45

✅ A. Absorb moisture and acids 💡 Explanation: Filter-driers trap debris, moisture, and acids that can damage compressor parts and oil. 📘 Key Concept: Replace filter-driers after burnouts or when system is opened for service.

Question 46

Q46. A pressure-enthalpy (P-H) diagram is used to: A. Determine superheat and subcooling B. Visualize refrigeration cycle and energy transfers C. Measure head pressure D. Adjust expansion valve

Answer 46

✅ B. Visualize refrigeration cycle and energy transfers 💡 Explanation: A P-H chart shows relationships between pressure, enthalpy, and refrigerant state throughout the cycle. 📘 Key Concept: Used to calculate performance metrics such as COP and enthalpy difference.

Question 47

Q47. When the discharge valve of a reciprocating compressor leaks, the result is: A. Low suction pressure and high discharge pressure B. High suction pressure and low discharge pressure C. High suction and high discharge pressure D. Low suction and low discharge pressure

Answer 47

✅ B. High suction pressure and low discharge pressure 💡 Explanation: Leaking discharge valves allow high-pressure vapor to reenter cylinders during suction stroke. 📘 Key Concept: Leads to reduced capacity, efficiency, and noisy compressor operation.

Question 48

Q48. The component that separates liquid refrigerant from vapor refrigerant is the: A. Receiver B. Accumulator C. Condenser D. Evaporator

Answer 48

✅ B. Accumulator 💡 Explanation: An accumulator ensures only vapor enters the compressor, storing excess liquid refrigerant temporarily. 📘 Key Concept: Common in low-temperature and heat pump systems to prevent liquid slugging.

Question 49

Q49. A condenser that uses both water and air for cooling is called a: A. Water-cooled condenser B. Air-cooled condenser C. Evaporative condenser D. Shell-and-tube condenser

Answer 49

✅ C. Evaporative condenser 💡 Explanation: Evaporative condensers spray water over coils while air passes through, combining water and air cooling for high efficiency. 📘 Key Concept: Used in large HVAC systems for reduced energy consumption and compact design.

Question 50

Q50. The safety device that prevents compressor damage from loss of oil pressure is the: A. Oil pressure safety switch B. High-pressure cutout C. Low-pressure control D. Thermal overload relay

Answer 50

✅ A. Oil pressure safety switch 💡 Explanation: It monitors differential oil pressure and shuts down the compressor if oil pressure falls below safe limits. 📘 Key Concept: Essential for protecting bearings and crankshaft from lubrication failure.

Question 51

Q51. What is the function of a crankcase heater on a compressor? A. Prevent oil foaming during startup B. Maintain high oil viscosity C. Cool the compressor motor D. Remove non-condensables

Answer 51

✅ A. Prevent oil foaming during startup 💡 Explanation: A crankcase heater keeps the oil warm during shutdown, preventing refrigerant migration and mixing with oil, which can cause foaming and damage on startup. 📘 Key Concept: Always energize crankcase heaters several hours before startup to vaporize refrigerant from oil.

Question 52

Q52. A high suction pressure accompanied by low discharge pressure indicates: A. Shortage of refrigerant B. Compressor valves leaking C. Dirty condenser D. Overcharged system

Answer 52

✅ B. Compressor valves leaking 💡 Explanation: Leaky valves allow discharge gas to flow back into suction side, reducing pressure differential. 📘 Key Concept: Results in poor cooling, high amperage, and inefficient operation.

Question 53

Q53. The primary reason for installing an oil separator is to: A. Prevent oil from reaching the evaporator B. Collect excess refrigerant C. Control compressor temperature D. Maintain proper oil pressure

Answer 53

✅ A. Prevent oil from reaching the evaporator 💡 Explanation: Oil separators trap oil in the discharge gas and return it to the compressor crankcase, ensuring good lubrication. 📘 Key Concept: Common in large systems with long piping runs or multiple compressors.

Question 54

Q54. What is the purpose of a discharge line muffler? A. Reduce vibration and pulsation noise B. Control refrigerant flow rate C. Maintain oil level D. Increase discharge temperature

Answer 54

✅ A. Reduce vibration and pulsation noise 💡 Explanation: The discharge muffler minimizes noise and pulsation from reciprocating compressors. 📘 Key Concept: Installed close to the compressor discharge outlet to improve acoustic comfort.

Question 55

Q55. The function of the suction accumulator is to: A. Store liquid refrigerant and prevent compressor slugging B. Maintain suction pressure C. Increase superheat D. Equalize oil pressure

Answer 55

✅ A. Store liquid refrigerant and prevent compressor slugging 💡 Explanation: Accumulators trap liquid refrigerant before it enters the compressor, allowing only vapor to pass through. 📘 Key Concept: Crucial in heat pumps and low-temp systems where liquid return risk is high.

Question 56

Q56. The presence of moisture in a refrigeration system can cause: A. Freezing at the expansion valve B. Increased head pressure C. Higher oil temperature D. Increased compressor cooling

Answer 56

✅ A. Freezing at the expansion valve 💡 Explanation: Moisture forms ice at the expansion device, restricting flow and disrupting system operation. 📘 Key Concept: Use filter-driers and deep vacuum evacuation to remove moisture during service.

Question 57

Q57. When charging a refrigeration system with liquid refrigerant into the high side, the compressor should be: A. Running B. Off C. Cycling on and off D. Operating at full load

Answer 57

✅ B. Off 💡 Explanation: Liquid charging is done with the compressor off to prevent damage from liquid slugging during startup. 📘 Key Concept: After partial liquid charge, switch to vapor charging once the system starts.

Question 58

Q58. What is the main purpose of a condenser fan in an air-cooled condenser? A. Increase condensing temperature B. Reject heat to ambient air C. Increase refrigerant subcooling D. Control suction pressure

Answer 58

✅ B. Reject heat to ambient air 💡 Explanation: The condenser fan forces ambient air across condenser coils to remove heat from the refrigerant. 📘 Key Concept: Maintains correct condensing pressure and system efficiency.

Question 59

Q59. A fouled evaporator coil will cause: A. High suction pressure B. Low suction pressure C. High discharge pressure D. Low superheat

Answer 59

✅ B. Low suction pressure 💡 Explanation: Restricted heat absorption results in less refrigerant vaporization, lowering suction pressure. 📘 Key Concept: Check for dirty fins, ice buildup, or airflow obstructions.

Question 60

Q60. The pressure relief device on a compressor is designed to: A. Release oil when pressure rises B. Protect compressor from overpressure C. Control oil flow rate D. Maintain suction pressure

Answer 60

✅ B. Protect compressor from overpressure 💡 Explanation: Relief valves open when internal pressure exceeds design limits, venting gas to prevent mechanical failure. 📘 Key Concept: Typically set to open at 10% above maximum allowable working pressure (MAWP).

Question 61

Q61. The main function of a suction line heat exchanger is to: A. Increase superheat and subcooling B. Decrease compressor discharge pressure C. Reduce suction superheat D. Lower condensing temperature

Answer 61

✅ A. Increase superheat and subcooling 💡 Explanation: The suction line heat exchanger transfers heat from the liquid line to the suction line, increasing superheat and subcooling. 📘 Key Concept: Improves system efficiency but may risk high discharge temperatures if excessive.

Question 62

Q62. What is the most accurate method for removing moisture from a refrigeration system? A. Replacing filter-drier B. Purging with nitrogen C. Evacuating with a vacuum pump D. Blowing out with compressed air

Answer 62

✅ C. Evacuating with a vacuum pump 💡 Explanation: Pulling a deep vacuum to below 500 microns ensures moisture and non-condensables are removed from the system. 📘 Key Concept: Use a two-stage vacuum pump and hold test to confirm dryness before charging.

Question 63

Q63. When a liquid receiver is overfilled, it can cause: A. Liquid carryover to compressor B. High head pressure C. Insufficient refrigerant charge D. Low condensing temperature

Answer 63

✅ B. High head pressure 💡 Explanation: An overfilled receiver reduces vapor space, leading to increased system pressure. 📘 Key Concept: Receivers should be filled to no more than 80% to allow for liquid expansion.

Question 64

Q64. The difference between the cut-in and cut-out pressures on a pressure control is called: A. Range B. Differential C. Offset D. Ratio

Answer 64

✅ B. Differential 💡 Explanation: Differential is the pressure difference between the points where the control cuts in and cuts out. 📘 Key Concept: Maintains compressor cycling stability and prevents rapid on/off operation.

Question 65

Q65. A thermostatic expansion valve sensing bulb should be installed: A. On top of the suction line at the evaporator outlet B. At the evaporator inlet C. On the bottom of a suction line D. At the compressor suction port

Answer 65

✅ A. On top of the suction line at the evaporator outlet 💡 Explanation: Mounting on top ensures proper sensing of vapor temperature and avoids oil interference. 📘 Key Concept: Securely clamp and insulate bulb for accurate superheat control.

Question 66

Q66. If a refrigeration system operates with low suction pressure and low head pressure, it likely indicates: A. Restricted metering device B. Overcharged system C. Dirty condenser D. High ambient temperature

Answer 66

✅ A. Restricted metering device 💡 Explanation: Flow restriction limits refrigerant to the evaporator, reducing both suction and head pressures. 📘 Key Concept: Common causes: clogged filter-drier, plugged TXV, or iced capillary tube.

Question 67

Q67. Which of the following is used to prevent refrigerant migration to the compressor during off-cycle? A. Crankcase heater B. Check valve C. Oil separator D. Solenoid valve

Answer 67

✅ A. Crankcase heater 💡 Explanation: The heater keeps oil warm to prevent refrigerant from condensing in the compressor during shutdown. 📘 Key Concept: Prevents liquid slugging on startup and maintains oil integrity.

Question 68

Q68. What is the purpose of a purge unit in a centrifugal chiller? A. Remove air and non-condensables B. Add refrigerant automatically C. Maintain suction pressure D. Remove oil from refrigerant

Answer 68

✅ A. Remove air and non-condensables 💡 Explanation: Purge units extract air and inert gases that infiltrate low-pressure chillers, preventing efficiency loss. 📘 Key Concept: Air in system raises condenser pressure and lowers heat transfer efficiency.

Question 69

Q69. The main reason for a compressor short-cycling on low pressure is: A. Oversized expansion valve B. Low refrigerant charge C. Dirty condenser D. High ambient temperature

Answer 69

✅ B. Low refrigerant charge 💡 Explanation: Insufficient charge reduces suction pressure, causing the low-pressure control to shut off the compressor repeatedly. 📘 Key Concept: Verify charge and check for leaks to correct short-cycling issues.

Question 70

Q70. When installing a refrigerant sight glass, it should be located: A. After the evaporator outlet B. In the suction line C. In the liquid line before the expansion valve D. Between compressor and condenser

Answer 70

✅ C. In the liquid line before the expansion valve 💡 Explanation: The sight glass shows refrigerant condition and includes a moisture indicator for system monitoring. 📘 Key Concept: Indicates charge level and moisture; bubbles suggest low charge or flashing.

Question 71

Q71. The purpose of a compressor oil separator is to: A. Remove refrigerant from the oil B. Return oil to the compressor crankcase C. Prevent moisture contamination D. Separate vapor from liquid refrigerant

Answer 71

✅ B. Return oil to the compressor crankcase 💡 Explanation: An oil separator collects oil from the discharge gas and returns it to the crankcase, preventing oil loss to the system. 📘 Key Concept: Essential for long piping runs or multi-compressor systems to maintain proper lubrication.

Question 72

Q72. Which of the following best describes a flooded condenser? A. A condenser that is completely filled with liquid refrigerant B. A condenser where refrigerant is pumped through tubes surrounded by water C. A condenser with liquid backup for subcooling D. A condenser that uses air and water for cooling

Answer 72

✅ C. A condenser with liquid backup for subcooling 💡 Explanation: A flooded condenser maintains a liquid seal to ensure full condensation and improved subcooling. 📘 Key Concept: Used in large chillers for high efficiency and stable head pressure.

Question 73

Q73. The component that prevents refrigerant from flowing backward when the compressor is off is the: A. Solenoid valve B. Check valve C. Relief valve D. Accumulator

Answer 73

✅ B. Check valve 💡 Explanation: A check valve allows flow in one direction only, preventing backflow of refrigerant into the compressor during off cycles. 📘 Key Concept: Installed in discharge or liquid lines to maintain system pressure balance.

Question 74

Q74. The function of an oil pressure differential switch is to: A. Shut down the compressor when oil pressure is too low B. Indicate oil level in the compressor C. Equalize oil pressure between compressors D. Maintain oil temperature

Answer 74

✅ A. Shut down the compressor when oil pressure is too low 💡 Explanation: The oil pressure differential switch compares crankcase oil pressure to suction pressure and stops compressor operation if the difference is insufficient. 📘 Key Concept: Protects bearings and crankshaft from lubrication failure.

Question 75

Q75. The sight glass in a refrigeration system shows: A. Oil level only B. Liquid refrigerant condition and moisture level C. Compressor discharge pressure D. Evaporator airflow rate

Answer 75

✅ B. Liquid refrigerant condition and moisture level 💡 Explanation: A sight glass indicates whether refrigerant is a solid column or flashing and also displays moisture via color change. 📘 Key Concept: Green = dry system; yellow = moisture present; bubbles = low charge or flashing liquid.

Question 76

Q76. What condition will cause a compressor to short-cycle on the high-pressure control? A. Restricted condenser airflow B. Low refrigerant charge C. Dirty evaporator D. Oversized expansion valve

Answer 76

✅ A. Restricted condenser airflow 💡 Explanation: Blocked or dirty condenser coils raise head pressure, causing the high-pressure control to trip repeatedly. 📘 Key Concept: Clean condenser coils and ensure proper fan operation to prevent short-cycling.

Question 77

Q77. The main purpose of an evaporator defrost system is to: A. Prevent refrigerant migration B. Remove ice buildup on the evaporator coil C. Maintain compressor temperature D. Lower discharge pressure

Answer 77

✅ B. Remove ice buildup on the evaporator coil 💡 Explanation: Defrosting removes frost and ice accumulation that restricts airflow and reduces cooling capacity. 📘 Key Concept: Common methods: electric heaters, hot gas defrost, or air defrost.

Question 78

Q78. The expansion valve sensing bulb controls refrigerant flow by responding to: A. Discharge pressure B. Evaporator outlet temperature C. Condenser temperature D. Compressor suction pressure

Answer 78

✅ B. Evaporator outlet temperature 💡 Explanation: The bulb senses temperature at the evaporator outlet, adjusting valve opening to maintain proper superheat. 📘 Key Concept: Prevents liquid refrigerant return and ensures stable evaporator operation.

Question 79

Q79. A thermostatic expansion valve maintains a constant: A. Evaporator pressure B. Suction pressure C. Degree of superheat D. Discharge temperature

Answer 79

✅ C. Degree of superheat 💡 Explanation: The TXV adjusts refrigerant flow so that vapor leaving the evaporator has consistent superheat. 📘 Key Concept: Balances load variations while protecting compressor from liquid return.

Question 80

Q80. The purpose of a pressure relief valve is to: A. Maintain suction pressure B. Equalize oil levels C. Prevent system overpressure D. Control evaporator temperature

Answer 80

✅ C. Prevent system overpressure 💡 Explanation: Pressure relief valves open to vent gas when system pressure exceeds safe design limits. 📘 Key Concept: Protects against mechanical damage; required by code on high-pressure vessels.

Question 81

Q81. The primary function of a refrigerant receiver is to: A. Store liquid refrigerant B. Accumulate suction gas C. Remove oil from refrigerant D. Regulate suction pressure

Answer 81

✅ A. Store liquid refrigerant 💡 Explanation: The receiver stores excess liquid refrigerant after condensation, ensuring a steady liquid supply to the expansion valve. 📘 Key Concept: Located after the condenser; allows for system charge control and refrigerant surge capacity.

Question 82

Q82. What is the most likely cause of a compressor running continuously without satisfying the thermostat? A. Dirty condenser B. Short cycling C. Low refrigerant charge D. Oversized expansion valve

Answer 82

✅ C. Low refrigerant charge 💡 Explanation: Insufficient charge reduces evaporator efficiency and capacity, causing long run times without meeting cooling demand. 📘 Key Concept: Check for leaks and recharge system to restore design performance.

Question 83

Q83. A liquid line solenoid valve is used to: A. Prevent refrigerant migration during off cycle B. Control suction pressure C. Maintain head pressure D. Separate oil from refrigerant

Answer 83

✅ A. Prevent refrigerant migration during off cycle 💡 Explanation: The solenoid valve closes when the thermostat is satisfied, stopping liquid flow to prevent migration or flooding. 📘 Key Concept: Common in pump-down systems to isolate high- and low-side pressures.

Question 84

Q84. What type of expansion device is commonly used in small refrigeration systems? A. Thermostatic expansion valve B. Float valve C. Capillary tube D. Electronic expansion valve

Answer 84

✅ C. Capillary tube 💡 Explanation: Capillary tubes are fixed-orifice devices that meter refrigerant based on pressure difference, ideal for small systems. 📘 Key Concept: Simple, low-cost, and maintenance-free but sensitive to system cleanliness.

Question 85

Q85. The suction line in a refrigeration system should be insulated to: A. Prevent condensation and heat gain B. Reduce refrigerant velocity C. Maintain head pressure D. Increase suction pressure

Answer 85

✅ A. Prevent condensation and heat gain 💡 Explanation: Insulating the suction line prevents unwanted heat absorption and condensation on cold surfaces. 📘 Key Concept: Maintains superheat stability and system efficiency.

Question 86

Q86. When charging refrigerant into the low side of a running system, it must be introduced as: A. Liquid refrigerant B. Vapor refrigerant C. Subcooled liquid D. Superheated vapor

Answer 86

✅ B. Vapor refrigerant 💡 Explanation: Charging vapor prevents liquid slugging that could damage the compressor. 📘 Key Concept: Always charge vapor into the suction side; liquid charging on high side is done only when system is off.

Question 87

Q87. The purpose of the accumulator in a heat pump system is to: A. Prevent liquid refrigerant from entering the compressor B. Store excess oil C. Separate air and refrigerant D. Control suction pressure

Answer 87

✅ A. Prevent liquid refrigerant from entering the compressor 💡 Explanation: Accumulators trap liquid refrigerant during low-load conditions, ensuring only vapor enters the compressor. 📘 Key Concept: Protects compressor from slugging during defrost and off cycles.

Question 88

Q88. Which of the following would cause low suction pressure and low discharge pressure? A. Undercharge or restriction in system B. Overcharge C. Dirty condenser D. Air in system

Answer 88

✅ A. Undercharge or restriction in system 💡 Explanation: A restricted metering device or low charge reduces refrigerant mass flow, leading to lower pressures throughout. 📘 Key Concept: Diagnose by checking superheat, subcooling, and sight glass conditions.

Question 89

Q89. The term 'superheat' refers to: A. Heat added to vapor above its saturation temperature B. Heat removed from liquid below saturation temperature C. Total heat absorbed during condensation D. Latent heat during evaporation

Answer 89

✅ A. Heat added to vapor above its saturation temperature 💡 Explanation: Superheat ensures vapor is completely dry before entering the compressor. 📘 Key Concept: Superheat = Actual suction temperature – Saturation temperature.

Question 90

Q90. The primary purpose of the condenser in a refrigeration system is to: A. Absorb heat from air B. Reject heat to surrounding medium C. Lower suction pressure D. Increase refrigerant volume

Answer 90

✅ B. Reject heat to surrounding medium 💡 Explanation: The condenser removes heat absorbed in the evaporator plus compressor heat, converting vapor to liquid. 📘 Key Concept: Completes the high-pressure side of the refrigeration cycle.

Question 91

Q91. When a refrigeration system operates with high head pressure and normal suction pressure, it may indicate: A. Overcharge or dirty condenser B. Undercharge C. Low load on evaporator D. Restricted liquid line

Answer 91

✅ A. Overcharge or dirty condenser 💡 Explanation: An overcharged system or dirty condenser causes heat rejection inefficiency, raising head pressure. 📘 Key Concept: Monitor subcooling and clean condenser coils; ensure proper refrigerant charge.

Question 92

Q92. What is the function of the metering device in a refrigeration system? A. Control refrigerant flow and reduce pressure B. Raise refrigerant pressure C. Absorb heat D. Separate liquid and vapor

Answer 92

✅ A. Control refrigerant flow and reduce pressure 💡 Explanation: The metering device meters refrigerant into the evaporator while dropping pressure from high to low side. 📘 Key Concept: Expansion devices include TXVs, capillary tubes, and electronic valves.

Question 93

Q93. In a water-cooled condenser, scaling on tubes will cause: A. Decrease in condensing pressure B. Increase in condensing pressure C. No effect on pressure D. Decrease in refrigerant flow

Answer 93

✅ B. Increase in condensing pressure 💡 Explanation: Scale buildup insulates tubes, reducing heat transfer and forcing higher condensing pressures. 📘 Key Concept: Prevent by periodic cleaning and using treated water.

Question 94

Q94. When refrigerant leaves the condenser, it is normally in what state? A. Superheated vapor B. Saturated vapor C. Subcooled liquid D. Two-phase mixture

Answer 94

✅ C. Subcooled liquid 💡 Explanation: The refrigerant condenses and is slightly subcooled before entering the expansion device. 📘 Key Concept: Subcooling ensures only liquid enters the expansion valve, preventing flashing.

Question 95

Q95. The refrigerant entering the evaporator is normally: A. Subcooled liquid B. Saturated liquid-vapor mixture C. Superheated vapor D. Subcooled vapor

Answer 95

✅ B. Saturated liquid-vapor mixture 💡 Explanation: The expansion valve meters refrigerant as a mixture that evaporates by absorbing heat. 📘 Key Concept: Evaporation converts liquid to vapor at low pressure and temperature.

Question 96

Q96. The most probable cause of liquid refrigerant returning to the compressor is: A. Overfeeding the evaporator B. Restricted metering device C. Dirty condenser D. Low oil level

Answer 96

✅ A. Overfeeding the evaporator 💡 Explanation: Excess liquid refrigerant fails to evaporate fully and can flood back to the compressor, causing damage. 📘 Key Concept: Check expansion valve superheat setting and load balance.

Question 97

Q97. The term 'latent heat' refers to: A. Heat that causes a change in temperature B. Heat that causes a change in state without temperature change C. Sensible heat absorbed by air D. Total heat content of a substance

Answer 97

✅ B. Heat that causes a change in state without temperature change 💡 Explanation: Latent heat is absorbed or released during phase changes like boiling or condensation. 📘 Key Concept: Measured in BTU/lb; essential to refrigeration and air conditioning.

Question 98

Q98. What happens if air enters a refrigeration system? A. System pressure increases B. Condensing pressure decreases C. Suction pressure increases D. Evaporator capacity improves

Answer 98

✅ A. System pressure increases 💡 Explanation: Air and other non-condensables occupy condenser space, increasing head pressure and reducing heat transfer. 📘 Key Concept: Purge non-condensables using proper service equipment to maintain efficiency.

Question 99

Q99. When a compressor runs but no cooling occurs, the probable cause is: A. Loss of refrigerant charge B. Dirty condenser C. Restricted airflow D. Overcharge

Answer 99

✅ A. Loss of refrigerant charge 💡 Explanation: Without sufficient refrigerant, the system cannot absorb or transfer heat, resulting in no cooling. 📘 Key Concept: Verify pressures and inspect for leaks before recharging.

Question 100

Q100. A high superheat reading indicates: A. Evaporator is flooded B. Evaporator is starved C. Normal charge D. Excessive oil return

Answer 100

✅ B. Evaporator is starved 💡 Explanation: High superheat means insufficient refrigerant in the evaporator, causing dry vapor and reduced cooling. 📘 Key Concept: Check TXV adjustment, refrigerant charge, and evaporator airflow.

Question 101

Q101. The purpose of a suction line accumulator is to: A. Prevent liquid refrigerant from entering the compressor B. Store oil for lubrication C. Control suction pressure D. Reduce discharge temperature

Answer 101

✅ A. Prevent liquid refrigerant from entering the compressor 💡 Explanation: Accumulators capture and hold liquid refrigerant returning from the evaporator, allowing only vapor to pass through to the compressor. 📘 Key Concept: Prevents liquid slugging and is commonly used in heat pumps and low-temperature systems.

Question 102

Q102. What is the function of the evaporator in a refrigeration system? A. Reject heat to the surroundings B. Absorb heat into the refrigerant C. Increase refrigerant pressure D. Store liquid refrigerant

Answer 102

✅ B. Absorb heat into the refrigerant 💡 Explanation: The evaporator absorbs heat from air or water, evaporating liquid refrigerant into vapor. 📘 Key Concept: This process produces the cooling effect in the refrigeration cycle.

Question 103

Q103. The crankcase heater in a compressor is used to: A. Keep oil temperature above refrigerant saturation point B. Reduce compressor vibration C. Maintain crankcase pressure D. Control oil flow rate

Answer 103

✅ A. Keep oil temperature above refrigerant saturation point 💡 Explanation: The heater prevents refrigerant from condensing in the oil during off cycles. 📘 Key Concept: Prevents oil dilution and liquid slugging at startup.

Question 104

Q104. A high head pressure combined with low suction pressure may indicate: A. System restriction or underfeeding B. Overcharge C. Dirty evaporator D. High ambient temperature

Answer 104

✅ A. System restriction or underfeeding 💡 Explanation: A blockage or restricted metering device limits refrigerant flow, causing high discharge and low suction pressures. 📘 Key Concept: Check for clogged filter-drier or restricted TXV.

Question 105

Q105. A low-pressure control switch is primarily used to: A. Protect the system from overpressure B. Cycle the compressor based on suction pressure C. Prevent oil foaming D. Regulate discharge temperature

Answer 105

✅ B. Cycle the compressor based on suction pressure 💡 Explanation: The low-pressure control starts and stops the compressor as suction pressure rises or falls within set limits. 📘 Key Concept: Also serves as protection against loss of charge or low load.

Question 106

Q106. The type of heat transfer that occurs in an evaporator is: A. Radiation B. Convection C. Conduction and convection D. Radiation and conduction

Answer 106

✅ C. Conduction and convection 💡 Explanation: Heat transfers from air to the evaporator coil surface (convection) and through the metal tube walls to the refrigerant (conduction). 📘 Key Concept: Both processes are essential for efficient heat absorption.

Question 107

Q107. When a system is overcharged with refrigerant, the most likely result is: A. Low head pressure B. High head pressure C. Low suction pressure D. High superheat

Answer 107

✅ B. High head pressure 💡 Explanation: Too much refrigerant raises condensing pressure and temperature, overloading the compressor. 📘 Key Concept: Proper charging ensures correct subcooling and system efficiency.

Question 108

Q108. What is the primary function of a compressor in a refrigeration system? A. Absorb heat from the evaporator B. Raise the pressure and temperature of refrigerant vapor C. Condense refrigerant into liquid D. Control refrigerant flow

Answer 108

✅ B. Raise the pressure and temperature of refrigerant vapor 💡 Explanation: The compressor compresses low-pressure vapor into high-pressure, high-temperature vapor for condensation. 📘 Key Concept: Acts as the pump that circulates refrigerant throughout the system.

Question 109

Q109. What is the effect of non-condensable gases in a refrigeration system? A. Lower head pressure B. Higher condensing pressure and reduced efficiency C. Stable operating conditions D. Lower discharge temperature

Answer 109

✅ B. Higher condensing pressure and reduced efficiency 💡 Explanation: Non-condensables take up space in the condenser, increasing head pressure and compressor work. 📘 Key Concept: Purge non-condensables to maintain efficiency and prevent overheating.

Question 110

Q110. The component that separates oil from refrigerant gas and returns it to the compressor is the: A. Oil separator B. Suction accumulator C. Receiver D. Evaporator

Answer 110

✅ A. Oil separator 💡 Explanation: The oil separator removes oil from discharge gas and returns it to the crankcase to ensure proper lubrication. 📘 Key Concept: Improves system performance by keeping oil where it belongs.

Question 111

Q111. The main advantage of a thermostatic expansion valve (TXV) over a capillary tube is that the TXV: A. Has fixed flow control B. Adjusts flow automatically with load changes C. Requires no sensing bulb D. Operates only at one pressure

Answer 111

✅ B. Adjusts flow automatically with load changes 💡 Explanation: The TXV maintains consistent superheat by modulating refrigerant flow based on evaporator load. 📘 Key Concept: Provides better efficiency and protects the compressor from liquid floodback.