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Refrigeration Operator B practice questions

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Question 1Refrigeration systems and components

In a basic vapor-compression refrigeration cycle, what is the primary function of the condenser?

  1. To reduce the refrigerant pressure before it enters the evaporator
  2. To absorb heat from the refrigerated space into the refrigerant
  3. To reject heat from the high-pressure refrigerant to the surrounding medium Correct answer.
  4. To separate lubricating oil from the discharge gas

Explanation

The condenser is the high-side heat exchanger where desuperheated, condensed refrigerant gives up heat to air or water. Removing that heat is what allows the refrigerant to liquefy so it can be expanded and reused. Heat absorption from the load occurs in the evaporator, and pressure reduction occurs at the metering device.

Question 2Refrigeration systems and components

A refrigerant enters the evaporator as a low-quality liquid-vapor mixture and leaves as saturated vapor. Which statement best describes the heat transfer that occurs inside the coil?

  1. Latent heat is absorbed as the liquid portion boils at nearly constant temperature. Correct answer.
  2. Sensible heat is removed while the refrigerant pressure rises.
  3. Superheat is removed before any boiling begins.
  4. Latent heat is rejected as vapor condenses on the tube walls.

Explanation

Boiling refrigerant absorbs latent heat at essentially constant saturation temperature and pressure, which is why the coil can hold a stable temperature. Sensible superheat is added only after all liquid has boiled away near the coil outlet. Condensation and heat rejection belong to the condenser side of the system.

Question 3Refrigeration systems and components

Which component raises the refrigerant from evaporator pressure to discharge pressure in a vapor-compression system?

  1. Evaporator pressure regulator
  2. Thermostatic expansion valve
  3. Compressor Correct answer.
  4. Receiver

Explanation

The compressor is the only device that adds work to the vapor and lifts it to condensing pressure. The expansion valve and evaporator pressure regulator both reduce or hold pressure rather than raise it. A receiver stores liquid and does not change pressure.

Question 4Refrigeration systems and components

A thermostatic expansion valve maintains superheat at the evaporator outlet. Which condition would cause the valve to open wider?

  1. The evaporator pressure rises above the valve's maximum operating pressure.
  2. The remote bulb senses warmer suction gas than the superheat setting requires. Correct answer.
  3. The liquid line temperature drops below the condensing temperature.
  4. The remote bulb senses colder suction gas than the superheat setting requires.

Explanation

The bulb charge pressure acts on one side of the diaphragm and opposes evaporator pressure plus spring force. When the bulb senses warmer gas, its pressure rises and pushes the valve further open, admitting more refrigerant to restore the superheat setting. Colder gas at the bulb would drive the valve toward closing.

Question 5Refrigeration systems and components

Why must a compressor's discharge line be routed with adequate slope and traps toward the condenser in some low-ambient installations?

  1. To prevent oil from draining back into the compressor during off cycles Correct answer.
  2. To increase the subcooling produced in the condenser
  3. To reduce the refrigerant charge required by the system
  4. To lower the discharge pressure seen by the compressor

Explanation

Sloping the discharge line and using traps helps keep oil moving toward the condenser and prevents liquid refrigerant or oil from draining back into the compressor head during shutdown. Oil returning to a hot compressor can cause slugging and lubrication problems. Charge, subcooling, and discharge pressure are not the purpose of this piping practice.

Question 6Refrigeration systems and components

What is the purpose of a liquid receiver in a refrigeration system?

  1. To separate oil from the discharge gas before condensing
  2. To provide a liquid seal for the compressor suction line
  3. To remove moisture from the refrigerant vapor
  4. To store liquid refrigerant and accommodate variations in system charge demand Correct answer.

Explanation

A receiver holds liquid refrigerant so the system can supply the expansion device under varying load and condenser conditions. It also provides storage when the charge is pumped down. Oil separation, suction sealing, and moisture removal are handled by other devices.

Question 7Refrigeration systems and components

A system uses a filter-drier in the liquid line. What is its primary function?

  1. To regulate the flow of refrigerant into the evaporator
  2. To reduce the pressure of the liquid before the expansion valve
  3. To remove moisture and solid contaminants from the liquid refrigerant Correct answer.
  4. To store excess refrigerant during low-load operation

Explanation

A filter-drier contains a desiccant and a filter element that capture moisture and particulate matter, protecting the expansion valve and compressor. Flow regulation and pressure reduction are functions of the expansion device. Storage is provided by the receiver.

Question 8Refrigeration systems and components

Which statement correctly describes the state of the refrigerant at the inlet to the compressor in a properly operating system?

  1. Two-phase mixture at high quality
  2. Saturated liquid at high pressure
  3. Superheated vapor at low pressure Correct answer.
  4. Subcooled liquid at condensing pressure

Explanation

Refrigerant reaching the compressor should be fully vaporized and slightly superheated to prevent liquid slugging. It is at low (suction) pressure because the compressor has not yet raised it. Liquid or two-phase refrigerant at the suction would indicate an overfeed or expansion valve problem.

Question 9Refrigeration systems and components

A reciprocating compressor uses a crankcase heater. What is its purpose?

  1. To warm the crankcase oil so refrigerant does not condense and dilute it during shutdown Correct answer.
  2. To raise the oil viscosity so it lubricates better at all times
  3. To prevent the compressor from starting at low ambient temperatures
  4. To increase the discharge pressure during cold weather

Explanation

During an off cycle, cold refrigerant can migrate to the crankcase and dissolve in the oil. The heater keeps the oil warm enough to discourage condensation and migration, protecting lubrication on startup. It is not a viscosity modifier, a low-ambient start lockout, or a discharge pressure control.

Question 10Refrigeration systems and components

What does a low-pressure control on the suction side of a refrigeration compressor typically do?

  1. Limits the maximum discharge pressure
  2. Cycles the compressor based on suction pressure setpoints Correct answer.
  3. Opens the hot gas bypass valve during low load
  4. Regulates the flow of liquid refrigerant to the evaporator

Explanation

A low-pressure control senses suction pressure and opens or closes its contacts at adjustable cut-in and cut-out setpoints, cycling the compressor to match load. High-pressure controls protect against excessive discharge pressure. Liquid flow is metered by the expansion device.

Question 11Refrigeration systems and components

A high-pressure cutout switch trips repeatedly on a water-cooled condenser system. Which condition is the most likely cause?

  1. Insufficient condenser water flow Correct answer.
  2. Refrigerant undercharge
  3. A stuck-open hot gas bypass valve
  4. Low evaporator load

Explanation

Inadequate water flow reduces heat rejection, so condensing pressure and temperature rise until the high-pressure cutout trips. Undercharge, low load, and an open hot gas bypass would tend to lower rather than raise discharge pressure. Checking water flow and approach temperature is the first diagnostic step.

Question 12Refrigeration systems and components

Which refrigerant property is most important when selecting a refrigerant for a system with a large evaporator pressure drop concern?

  1. High critical temperature Correct answer.
  2. High latent heat of vaporization
  3. Low ozone depletion potential
  4. Low molecular weight and low density

Explanation

A high critical temperature allows the refrigerant to condense at typical ambient conditions and supports efficient operation across a wide range. Latent heat affects charge and flow rates, and molecular weight affects pressure drop and compressor displacement. Ozone depletion potential is an environmental characteristic, not the property governing this concern.

Question 13Refrigeration systems and components

What is the function of an accumulator in a refrigeration system?

  1. To increase the pressure of the suction vapor
  2. To prevent liquid refrigerant from reaching the compressor Correct answer.
  3. To remove non-condensable gases from the condenser
  4. To store liquid refrigerant on the high side

Explanation

An accumulator is installed in the suction line to trap any liquid refrigerant that carries over, allowing it to boil off before vapor reaches the compressor. High-side liquid storage is the receiver's role. Non-condensable removal is done by purging, and pressure increase is the compressor's job.

Question 14Refrigeration systems and components

A system shows low suction pressure, high superheat, and a frosted suction line right at the expansion valve outlet. Which condition best fits these symptoms?

  1. Overcharge of refrigerant
  2. Too much condenser subcooling
  3. A failed condenser fan
  4. A restricted or plugged expansion valve screen Correct answer.

Explanation

A restriction at the expansion valve starves the evaporator, producing low suction pressure and high superheat, with frost forming where the pressure drop occurs. Overcharge and excess subcooling would tend to raise suction pressure and reduce superheat. A failed condenser fan raises discharge pressure but does not create this suction-side pattern.

Question 15Refrigeration systems and components

Which device is used to maintain a constant evaporator pressure when the load varies, such as in a system with multiple evaporators at different temperatures?

  1. Thermostatic expansion valve
  2. Solenoid valve
  3. Check valve
  4. Evaporator pressure regulator Correct answer.

Explanation

An evaporator pressure regulator throttles suction gas to hold a minimum evaporator pressure, preventing the coil from dropping below its design temperature. The expansion valve controls superheat, a solenoid starts and stops flow, and a check valve enforces one-way flow.

Question 16Refrigeration systems and components

In a refrigeration system, what is the effect of non-condensable gases such as air in the condenser?

  1. They raise condensing pressure and reduce system efficiency Correct answer.
  2. They lower condensing pressure and improve capacity
  3. They have no measurable effect on operation
  4. They increase the latent heat of the refrigerant

Explanation

Non-condensable gases collect in the condenser and raise the partial pressure required to condense the refrigerant, so discharge pressure and compressor work increase while capacity falls. They must be purged from the high side. They do not improve capacity or change the refrigerant's latent heat.

Question 17Refrigeration systems and components

What is the primary purpose of subcooling the liquid refrigerant leaving the condenser?

  1. To reduce the compressor displacement required
  2. To increase the superheat at the compressor suction
  3. To raise the evaporator pressure
  4. To ensure a solid column of liquid reaches the expansion valve Correct answer.

Explanation

Subcooling guarantees that the refrigerant is fully liquid, so the expansion valve receives a solid column and meters correctly. It also slightly increases net refrigeration effect. Superheat is controlled at the evaporator outlet, and subcooling does not raise evaporator pressure or change compressor displacement.

Question 18Refrigeration systems and components

A solenoid valve installed in the liquid line of a pump-down system is wired to close when the thermostat is satisfied. What is the purpose of this arrangement?

  1. To relieve excess pressure from the receiver
  2. To bypass hot gas during low-load conditions
  3. To modulate refrigerant flow to maintain superheat
  4. To stop liquid flow so the compressor can pump the low side down to a set pressure Correct answer.

Explanation

Closing the liquid line solenoid stops the feed of refrigerant, allowing the compressor to pump the low side into the receiver until the low-pressure control stops it. This limits the amount of refrigerant left in the evaporator during off cycles. Superheat control, hot gas bypass, and pressure relief are separate functions.

Question 19Refrigeration systems and components

Which statement best describes the difference between a thermostatic expansion valve and a capillary tube as metering devices?

  1. The expansion valve modulates to hold superheat, while the capillary tube provides a fixed restriction. Correct answer.
  2. Both devices modulate flow in response to suction superheat.
  3. The expansion valve provides a fixed restriction, while the capillary tube modulates superheat.
  4. Neither device reduces refrigerant pressure.

Explanation

A thermostatic expansion valve uses a sensing bulb to vary its opening and hold superheat at the evaporator outlet. A capillary tube is a fixed-length restriction whose flow varies only with pressure difference. Both reduce pressure, but only the expansion valve actively modulates.

Question 20Refrigeration systems and components

What does a compressor's service valve in the back-seated position do?

  1. Closes the gauge port while leaving the main line open Correct answer.
  2. Opens both the main line and the gauge port
  3. Closes the main line while opening the gauge port
  4. Isolates the compressor from both the system and the gauge port

Explanation

Back-seating a service valve turns the stem out fully, sealing the gauge port and leaving the main refrigerant line fully open for normal operation. Front-seating closes the main line. Mid-position opens both the line and the gauge port for reading pressures.

Question 21Refrigeration systems and components

A compressor is tripping its internal overload shortly after startup on a hot day. Which condition is a plausible cause?

  1. A closed liquid line solenoid during the off cycle
  2. Low suction pressure with high superheat
  3. A properly charged system at design load
  4. High discharge pressure causing high current draw Correct answer.

Explanation

High discharge pressure raises compressor current and motor temperature, which can trip the internal overload. Low suction pressure with high superheat tends to reduce mass flow and current. A closed solenoid is normal during off cycles, and a properly charged system at design load should not trip.

Question 22Refrigeration systems and components

Which of the following is a function of the oil separator in a refrigeration system?

  1. To cool the compressor motor windings
  2. To regulate the oil pressure delivered to the bearings
  3. To remove oil from the discharge gas and return it to the compressor Correct answer.
  4. To filter moisture from the liquid refrigerant

Explanation

An oil separator removes entrained oil from hot discharge gas and directs it back to the crankcase, keeping oil out of the condenser and evaporator. Moisture removal is the filter-drier's job, motor cooling is handled by suction gas or another method, and oil pressure regulation is done by the oil pump and pressure controls.

Question 23Refrigeration systems and components

A technician observes that the sight glass in the liquid line shows bubbles continuously during stable operation. Which interpretation is most reasonable?

  1. The system is correctly charged and operating normally
  2. The evaporator is flooding with liquid refrigerant
  3. The system may be low on charge or have a restriction causing flash gas Correct answer.
  4. The condenser is over-cooled and producing excess subcooling

Explanation

Continuous bubbles at a steady load often indicate insufficient charge or a restriction that causes the liquid to flash before the expansion valve. A brief bubble pattern during load changes can be normal, but persistent bubbling warrants checking subcooling and the liquid line. Excess subcooling and evaporator flooding would not produce this symptom.

Question 24Refrigeration systems and components

What is the purpose of a condenser's subcooler circuit in some systems?

  1. To increase the superheat of the suction gas
  2. To remove non-condensable gases from the condenser
  3. To further cool liquid refrigerant below condensing temperature before it leaves the condenser Correct answer.
  4. To provide a bypass around the expansion valve

Explanation

A subcooler circuit removes additional heat from liquid refrigerant after it has condensed, increasing subcooling and improving expansion valve performance. It does not purge non-condensables or affect suction superheat. Bypassing the expansion valve is not its purpose.

Question 25Refrigeration systems and components

A direct-expansion evaporator is described as operating with 10°F superheat at the outlet. What does this mean?

  1. The refrigerant is 10°F below its saturation temperature at the outlet.
  2. The suction gas is 10°F warmer than the saturation temperature corresponding to its pressure. Correct answer.
  3. The evaporator is 10°F colder than the refrigerated space.
  4. The liquid line is 10°F cooler than the condensing temperature.

Explanation

Superheat is the difference between the actual vapor temperature and the saturation temperature at the same pressure. A 10°F superheat means the gas has been warmed 10°F beyond saturation, confirming complete vaporization. A temperature below saturation would be subcooling, not superheat.

Question 26Refrigeration systems and components

A refrigeration system uses a thermostatic expansion valve with an external equalizer line. What is the purpose of the external equalizer?

  1. It compensates the valve opening for the pressure drop across the evaporator Correct answer.
  2. It limits the maximum operating pressure of the valve body
  3. It adds refrigerant charge to the bulb to speed valve response
  4. It bypasses hot gas around the condenser during low ambient

Explanation

The external equalizer connects the underside of the diaphragm to the evaporator outlet, so the valve senses true outlet pressure rather than the pressure at the valve inlet. This compensates for the pressure drop through the evaporator coil and distributor. Without it, the valve would behave as if superheat were higher than it actually is.

Question 27Refrigeration systems and components

An evaporator is fed by a flooded-type arrangement with a surge drum. How is the refrigerant flow through the evaporator tubes best described?

  1. Refrigerant is fully vaporized before it leaves the last tube pass
  2. Refrigerant is metered into each tube circuit by its own thermostatic valve
  3. Refrigerant passes through the tubes only once in a single pass
  4. Liquid refrigerant circulates through the tubes with only part of it boiling off Correct answer.

Explanation

In a flooded evaporator the tubes are essentially full of liquid, and only a portion of that liquid boils off as it absorbs heat. The remaining liquid returns to the surge drum, where vapor separates and liquid recirculates. This is why flooded evaporators are associated with liquid recirculation rates above one.

Question 28Refrigeration systems and components

A suction-line heat exchanger is installed so that cold suction gas pre-cools the warm liquid line. What is the main operational trade-off of this arrangement?

  1. It increases liquid subcooling but raises compressor discharge temperature and suction superheat Correct answer.
  2. It eliminates the need for a metering device at the evaporator
  3. It reduces compressor discharge temperature but decreases liquid subcooling
  4. It lowers the condensing pressure required for a given ambient

Explanation

The exchanger transfers heat from the liquid line to the suction gas, giving more subcooling and usually more refrigerating effect per kilogram of liquid. The cost is that the suction gas arrives hotter, which raises superheat at the compressor and increases discharge temperature. On high-compression-ratio systems this can stress the compressor and lubricant.

Question 29Refrigeration systems and components

What is the function of a check valve installed in the discharge line of a compressor in a parallel rack system?

  1. It blocks backflow of high-pressure gas through a stopped compressor Correct answer.
  2. It separates oil from the discharge gas before the condenser
  3. It regulates discharge pressure to a fixed setpoint
  4. It prevents reverse rotation of the compressor during pump-down

Explanation

A discharge-line check valve closes when a compressor stops, preventing high-pressure discharge gas from flowing back through that compressor from the common discharge header. This protects the idle compressor from hot gas migration and rotor spin. It is a one-way flow device, not a regulator.

Question 30Refrigeration systems and components

A condenser is specified as having a 10°F approach temperature. What does this value describe?

  1. The difference between condensing temperature and the leaving cooling-medium temperature Correct answer.
  2. The amount by which the liquid is cooled below condensing temperature
  3. The difference between entering and leaving cooling-medium temperatures
  4. The difference between suction and discharge pressures expressed as temperature

Explanation

Approach temperature is the gap between the refrigerant condensing temperature and the temperature of the cooling medium leaving the condenser. A small approach indicates an efficient condenser with good heat transfer. It is a performance indicator used to judge fouling or air-binding.

Question 31Refrigeration systems and components

An oil separator of the impingement type is installed on a compressor discharge line. On which line does the separated oil normally return to the compressor?

  1. Through the liquid line ahead of the expansion valve
  2. Through the equalizer line of the thermostatic expansion valve
  3. Through a small metering orifice or float arrangement back to the crankcase Correct answer.
  4. Through the suction line by way of the evaporator

Explanation

Separated oil collects in the separator sump and returns to the compressor crankcase through a small bleed orifice or a float-operated valve. The restriction limits how much high-pressure gas travels with the oil. Returning oil through the evaporator would defeat the purpose of separating it in the first place.

Question 32Refrigeration systems and components

A system has a suction pressure that is lower than normal, normal discharge pressure, and the evaporator is starved of liquid. Which component is the most likely cause?

  1. A crankcase heater stuck energized
  2. A condenser fan cycling on a mild day
  3. A restricted liquid-line filter-drier Correct answer.
  4. A condenser water-regulating valve stuck open

Explanation

A restricted filter-drier limits liquid flow to the metering device, so the evaporator receives too little refrigerant and suction pressure falls while discharge pressure stays near normal. The starvation pattern points to the liquid feed path. Condenser-side faults would normally show up as abnormal discharge pressure.

Question 33Refrigeration systems and components

Which statement correctly describes the operation of a hot-gas bypass valve used for capacity control?

  1. It injects discharge gas into the suction line to keep suction pressure from falling too low Correct answer.
  2. It bypasses the condenser to increase subcooling at part load
  3. It opens the liquid line to the suction line to raise superheat
  4. It dumps discharge gas to the atmosphere to limit condensing pressure

Explanation

A hot-gas bypass valve admits discharge gas into the suction side when evaporator load drops, holding suction pressure above a minimum setpoint. This keeps the compressor running within its safe operating envelope at low load. It is a capacity-control device, not a pressure-relief or subcooling device.

Question 34Refrigeration systems and components

A pressure-relief valve is installed on a liquid receiver. Why must the discharge of this valve be piped to a safe location?

  1. To prevent the receiver from becoming subcooled
  2. To allow the valve to reseat properly after relieving
  3. To provide a path for oil to drain from the receiver
  4. To carry away refrigerant vapor released during overpressure without endangering people Correct answer.

Explanation

When receiver pressure exceeds the valve setting, refrigerant vapor is released. Piping that discharge to a safe location keeps the released refrigerant away from occupied areas and personnel. The relief path also must be sized so the valve can pass its rated capacity.

Question 35Refrigeration systems and components

A technician finds frost forming on the outside of a suction-line solenoid valve body while the valve is energized. Which condition best explains this?

  1. The valve coil is drawing excessive current and overheating
  2. The valve is partially restricted, causing a pressure drop and localized cooling Correct answer.
  3. The valve seat is leaking refrigerant to the atmosphere
  4. The valve is oversized for the line and is acting as a receiver

Explanation

A restriction across a solenoid valve produces a pressure drop, and the resulting lower saturation temperature can chill the valve body below freezing so frost forms. This points to a partially blocked or undersized valve rather than an electrical problem. A fully open, unrestricted valve would not create that localized cold spot.

Question 36Refrigeration systems and components

Which device is used to maintain a constant evaporator pressure when the load varies, such as in a system with multiple evaporators?

  1. Evaporator pressure regulator Correct answer.
  2. Suction-line accumulator
  3. Thermostatic expansion valve
  4. Liquid-line filter-drier

Explanation

An evaporator pressure regulator is installed in the suction line from an evaporator and throttles to hold that evaporator at a minimum pressure. This protects against coil freezing when load drops and lets evaporators at different temperatures share a common suction header. It is a pressure-holding device rather than a metering or storage device.

Question 37Refrigeration systems and components

A system uses a capillary tube as its metering device. How does the charge in the system affect its operation compared with a thermostatic expansion valve?

  1. The tube requires a sensing bulb and equalizer to operate
  2. Charge has no effect because the tube is a fixed orifice
  3. The tube automatically adjusts to maintain constant superheat
  4. The system charge strongly affects performance, so charge must be set accurately Correct answer.

Explanation

A capillary tube has no modulating element, so its performance depends on the system charge and the pressure difference across it. Undercharge causes excessive superheat and starvation, while overcharge raises suction pressure and can flood the compressor. This is why critically charged systems require accurate weighing of the charge.

Question 38Refrigeration systems and components

A compressor's suction service valve is front-seated while the compressor is running. What is the effect on the compressor?

  1. The crankcase is vented to atmosphere through the gauge port
  2. The compressor is connected to the suction line through the gauge port only
  3. The compressor discharge is blocked, causing immediate high-pressure trip
  4. The compressor is isolated from the suction line and will pull into a vacuum Correct answer.

Explanation

Front-seating the suction service valve closes the passage from the suction line to the compressor, leaving only the gauge port connection. With the compressor running, it will evacuate its own crankcase and pull into a vacuum. This is done only briefly and with care during service procedures.

Question 39Refrigeration systems and components

A refrigerant is described as having a high latent heat of vaporization. What does this mean for system design?

  1. A smaller refrigerant mass flow is needed for a given cooling capacity Correct answer.
  2. The compressor must displace a larger volume of gas per unit of capacity
  3. The condenser must be larger because less heat is rejected
  4. The expansion valve must be oversized to pass the required flow

Explanation

Latent heat of vaporization is the heat absorbed per unit mass when liquid boils. A higher value means each kilogram of refrigerant carries more cooling effect, so less mass flow is required for a given capacity. Mass flow, not volume, is what this property directly affects.

Question 40Refrigeration systems and components

A liquid-line filter-drier is installed with the arrow on its body pointing in the direction of refrigerant flow toward the expansion valve. During a service call, a technician finds the shell of the drier is frosted and the pressure drop across it is much higher than normal. What is the most likely explanation for this condition?

  1. The drier is oversized for the system capacity, so refrigerant velocity through the shell is too low to keep it warm
  2. The system charge is over the nameplate amount, so liquid backs up in the liquid line and chills the drier shell
  3. The desiccant has broken down or the screen is plugged, restricting flow and causing a pressure drop with flashing across the restriction Correct answer.
  4. The arrow on the drier body was installed backwards, which reverses the flow direction through the desiccant

Explanation

A filter-drier is a flow-restricting component, and a large pressure drop across it means the outlet pressure falls below the saturation pressure for the liquid temperature, so part of the liquid flashes and the shell goes cold and frosts. The usual causes are a saturated or disintegrated desiccant, a plugged screen, or wax and sludge loading. The correct response is to replace the drier and find the source of the contamination, not to adjust charge.

Question 41Refrigerants and refrigeration cycles

In a basic vapor-compression refrigeration cycle, what is the function of the metering device?

  1. It raises refrigerant pressure and temperature before the condenser
  2. It stores liquid refrigerant for low-load periods
  3. It removes moisture and acid from the liquid line
  4. It reduces refrigerant pressure and temperature before the evaporator Correct answer.

Explanation

The metering device throttles refrigerant from condensing pressure to evaporating pressure, which also drops its temperature so it can absorb heat in the evaporator. It does not add energy; the compressor is the component that raises pressure and temperature.

Question 42Refrigerants and refrigeration cycles

Which refrigerant is classified as an A1 refrigerant under ASHRAE Standard 34?

  1. R-717 (ammonia)
  2. R-290 (propane)
  3. R-123
  4. R-134a Correct answer.

Explanation

R-134a has low toxicity and no flame propagation, which places it in safety group A1. Ammonia is B2L, propane is A3, and R-123 is B1, so each of those fails the A1 criteria.

Question 43Refrigerants and refrigeration cycles

A technician reads a saturated evaporator temperature of -10°C and a suction line temperature of -4°C at the evaporator outlet. What is the superheat?

  1. 10 K
  2. 6 K Correct answer.
  3. 14 K
  4. 4 K

Explanation

Superheat is the difference between the actual suction line temperature and the saturated evaporating temperature. Subtracting -10°C from -4°C gives 6 K of superheat.

Question 44Refrigerants and refrigeration cycles

What is the primary purpose of subcooling in a refrigeration system?

  1. To guarantee oil returns to the compressor
  2. To reduce the compressor discharge temperature
  3. To ensure only liquid reaches the metering device Correct answer.
  4. To prevent the evaporator from frosting

Explanation

Subcooling removes additional heat from liquid refrigerant after it leaves the condenser, ensuring a solid liquid column reaches the metering device and preventing flash gas at the expansion valve inlet. Oil return and evaporator frosting are controlled by other design factors.

Question 45Refrigerants and refrigeration cycles

In a reciprocating compressor, what happens to the volumetric efficiency as the compression ratio increases?

  1. It remains constant regardless of ratio
  2. It increases until the ratio exceeds 10:1
  3. It decreases because of re-expansion of clearance gas Correct answer.
  4. It increases because more gas is trapped

Explanation

Higher compression ratios cause the gas trapped in the clearance volume to re-expand further on the downstroke, reducing the volume actually drawn in. This lowers volumetric efficiency.

Question 46Refrigerants and refrigeration cycles

Which statement describes the state of refrigerant at the inlet to the evaporator?

  1. Low-pressure liquid-vapor mixture Correct answer.
  2. Low-pressure superheated vapor
  3. High-pressure superheated vapor
  4. High-pressure subcooled liquid

Explanation

After passing through the metering device, refrigerant flashes to a low-pressure, low-temperature liquid-vapor mixture before entering the evaporator. It becomes superheated vapor only at the evaporator outlet.

Question 47Refrigerants and refrigeration cycles

What is the effect of a non-condensable gas such as air in a refrigeration system?

  1. It improves heat transfer in the condenser
  2. It raises condensing pressure and increases compressor power Correct answer.
  3. It lowers condensing pressure and improves capacity
  4. It has no measurable effect on system performance

Explanation

Non-condensable gases collect in the condenser and occupy volume, raising the condensing pressure for a given condensing temperature. The compressor must then work against a higher head, increasing power and reducing capacity.

Question 48Refrigerants and refrigeration cycles

Which refrigerant has the lowest ozone depletion potential among the following?

  1. R-502
  2. R-12
  3. R-22
  4. R-134a Correct answer.

Explanation

R-134a is a hydrofluorocarbon with an ozone depletion potential of zero because it contains no chlorine or bromine. R-22, R-12, and R-502 all contain chlorine and have ODP values above zero.

Question 49Refrigerants and refrigeration cycles

A system using R-404A shows a bubble point of -30°C and a dew point of -26°C in the evaporator. Which temperature should be used as the evaporating temperature for superheat calculations?

  1. The bubble point of -30°C
  2. The average of -28°C
  3. The arithmetic sum of -56°C
  4. The dew point of -26°C Correct answer.

Explanation

R-404A is a zeotropic blend, so its temperature glides during evaporation. Superheat is measured against the dew point because that is the temperature at which the last liquid boils off at the evaporator outlet.

Question 50Refrigerants and refrigeration cycles

What is the purpose of a liquid-line sight glass with a moisture indicator?

  1. To display the suction pressure
  2. To show whether the system is fully charged and dry Correct answer.
  3. To measure the evaporator superheat
  4. To indicate compressor oil level

Explanation

A sight glass lets the operator see bubbles that indicate an undercharge or flash gas, and the moisture indicator changes color when moisture is present. Together they give a quick visual check on charge and dryness.