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BTEB Refrigeration & AC Exam study materials
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BTEB Refrigeration & AC Exam practice questions

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Question 1Refrigeration Fundamentals

In a vapour-compression refrigeration cycle, which component raises the refrigerant pressure from the evaporator pressure to the condenser pressure?

  1. The condenser
  2. The expansion valve
  3. The compressor Correct answer.
  4. The evaporator

Explanation

The compressor is the only component that adds work to the refrigerant, and it does so by raising its pressure from the low evaporator pressure to the high condenser pressure. The expansion valve does the opposite, dropping pressure. The two heat exchangers operate at roughly constant pressure.

Question 2Refrigeration Fundamentals

What is the primary function of the evaporator in a refrigeration system?

  1. To absorb heat from the refrigerated space while the liquid refrigerant boils Correct answer.
  2. To reject heat to the surroundings and condense the refrigerant
  3. To separate lubricating oil from the discharge gas
  4. To meter refrigerant flow into the coil

Explanation

The evaporator is the low-pressure heat exchanger where liquid refrigerant boils and, in doing so, absorbs heat from the space or product being cooled. It is the point where useful cooling is produced. Heat rejection happens in the condenser instead.

Question 3Refrigeration Fundamentals

Which refrigerant designation indicates a zeotropic blend whose components may fractionate if it leaks?

  1. R-407C Correct answer.
  2. R-717
  3. R-744
  4. R-134a

Explanation

The 400-series numbering denotes zeotropic blends, which change composition as they leak or boil because their components have different volatilities. R-407C is such a blend. Single-component refrigerants keep a constant composition.

Question 4Refrigeration Fundamentals

In a vapour-compression cycle, what is the effect of lowering the evaporating temperature while the condensing temperature stays fixed?

  1. The pressure ratio increases and the coefficient of performance decreases Correct answer.
  2. The mass flow of refrigerant required for a given capacity decreases
  3. The coefficient of performance stays unchanged because only the condenser matters
  4. The refrigerating effect per kilogram increases and compressor work falls

Explanation

Lowering the evaporating temperature widens the gap between suction and discharge pressures, so the pressure ratio rises. The compressor must work harder per unit of cooling, and the coefficient of performance falls. This is why deep-freeze operation is less efficient than air conditioning.

Question 5Refrigeration Fundamentals

What does the term 'sensible heat' describe?

  1. Heat that changes the temperature of a substance without changing its phase Correct answer.
  2. Heat lost through insulation by radiation only
  3. Heat generated by the compressor motor winding
  4. Heat absorbed or released during a change of state at constant temperature

Explanation

Sensible heat is the heat that produces a measurable temperature change in a substance without altering its phase. It contrasts with latent heat, which is absorbed or released during a phase change at constant temperature.

Question 6Refrigeration Fundamentals

Approximately how much heat must be removed to freeze 1 kg of water at 0 °C into ice at 0 °C, given a latent heat of fusion of about 334 kJ/kg?

  1. About 2.1 kJ
  2. About 4.2 kJ
  3. About 2260 kJ
  4. About 334 kJ Correct answer.

Explanation

Freezing at constant temperature involves only the latent heat of fusion, which for water is roughly 334 kJ per kilogram. No sensible cooling is needed because the water is already at 0 °C. The large value explains why ice-making is energy intensive.

Question 7Refrigeration Fundamentals

Which statement correctly describes the pressure–enthalpy diagram of a simple vapour-compression cycle?

  1. The expansion process is drawn as a vertical line at constant enthalpy Correct answer.
  2. The compressor process is drawn as a vertical line at constant pressure
  3. The condenser process is drawn as a curve of increasing entropy
  4. The evaporator process is drawn as a vertical line at constant temperature

Explanation

On a pressure–enthalpy diagram, the expansion device is modelled as a throttling process at constant enthalpy, so it appears as a vertical line. The compressor appears as a curve of rising enthalpy and pressure. The heat exchangers appear as horizontal lines at constant pressure.

Question 8Refrigeration Fundamentals

Which of the following is the standard boiling point of refrigerant R-134a at atmospheric pressure?

  1. About −40 °C
  2. About −15 °C
  3. About 0 °C
  4. About −26 °C Correct answer.

Explanation

R-134a boils at approximately −26 °C at one atmosphere, which suits medium-temperature refrigeration and air conditioning. Its boiling point is higher than that of R-404A or ammonia. Knowing boiling points helps match a refrigerant to an application.

Question 9Refrigeration Fundamentals

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

  1. To increase the suction pressure before the compressor
  2. To store liquid refrigerant and accommodate changes in charge distribution Correct answer.
  3. To remove moisture from the refrigerant
  4. To cool the compressor crankcase oil

Explanation

A receiver holds the surplus liquid refrigerant and provides storage so the system can respond to varying load and charge distribution. It is normally fitted on the high-pressure side after the condenser. Moisture removal and filtration are handled by other devices.

Question 10Refrigeration Fundamentals

A refrigeration system uses a thermostatic expansion valve. What controls the amount of refrigerant it admits to the evaporator?

  1. The ambient temperature around the condenser
  2. The pressure difference across the compressor
  3. The condensing pressure alone
  4. The degree of superheat at the evaporator outlet Correct answer.

Explanation

A thermostatic expansion valve senses the superheat at the evaporator outlet through its bulb and modulates the opening to maintain a set superheat. This keeps the evaporator properly fed without flooding liquid back to the compressor.

Question 11Refrigeration Fundamentals

Why is superheat desirable at the outlet of an evaporator?

  1. It ensures only vapour, not liquid droplets, reaches the compressor Correct answer.
  2. It increases the condensing temperature
  3. It eliminates the need for an expansion device
  4. It reduces the compressor discharge pressure

Explanation

A small amount of superheat guarantees that all liquid has boiled off before the gas leaves the evaporator. This protects the compressor from liquid slugging, which can cause mechanical damage and oil dilution. Superheat also provides the signal used by thermostatic expansion valves.

Question 12Refrigeration Fundamentals

What is the function of the condenser in a refrigeration cycle?

  1. To reject heat from the hot refrigerant gas so that it condenses to liquid Correct answer.
  2. To store refrigerant vapour for the compressor
  3. To reduce refrigerant pressure before the evaporator
  4. To absorb heat from the refrigerated space

Explanation

The condenser removes heat from the high-pressure discharge gas, first desuperheating it and then condensing it to liquid. The rejected heat is the sum of the heat absorbed in the evaporator and the compressor work.

Question 13Refrigeration Fundamentals

Which of the following best explains why ammonia is widely used in large industrial refrigeration plants despite its toxicity?

  1. It is completely odourless and therefore easy to detect
  2. It operates only at very low pressures
  3. It has a very high coefficient of performance and a low environmental impact Correct answer.
  4. It is non-flammable at all concentrations

Explanation

Ammonia has excellent thermodynamic properties, giving high efficiency, and it has zero ozone depletion potential and negligible global warming potential. Its sharp odour actually aids leak detection. These advantages make it attractive for large industrial plants where trained operators are available.

Question 14Refrigeration Fundamentals

What is the purpose of a crankcase heater on a compressor?

  1. To cool the compressor motor during operation
  2. To heat the discharge gas before it enters the condenser
  3. To raise the suction pressure at start-up
  4. To warm the oil so refrigerant does not accumulate and dilute it during shutdown Correct answer.

Explanation

During shutdown, refrigerant can migrate to the coldest point, often the crankcase, and dissolve in the oil. A crankcase heater keeps the oil warm so refrigerant does not accumulate, preventing oil dilution and foaming at start-up.

Question 15Refrigeration Fundamentals

Which type of compressor is most commonly used in small domestic refrigerators?

  1. A centrifugal compressor
  2. A hermetic reciprocating compressor Correct answer.
  3. A screw compressor
  4. An open-drive rotary vane compressor

Explanation

Small domestic refrigerators typically use a hermetic reciprocating compressor, in which the motor and compressor are sealed in one casing. This design is compact, cheap and leak-resistant. Centrifugal and screw compressors suit much larger capacities.

Question 16Refrigeration Fundamentals

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

  1. The amount of moisture dissolved in the refrigerant
  2. The pressure drop across the expansion valve
  3. The temperature difference between the liquid and the condensing temperature Correct answer.
  4. The temperature rise caused by the compressor

Explanation

Subcooling is the number of degrees the liquid refrigerant is cooled below its condensing temperature. It confirms that the condenser is adequately charged and performing well. Measuring subcooling helps diagnose undercharge and condenser problems.

Question 17Refrigeration Fundamentals

In a cascade refrigeration system, why are two separate refrigerant circuits used?

  1. To avoid the use of an expansion device
  2. To allow each circuit to operate over a limited, efficient pressure range Correct answer.
  3. To eliminate the need for any compressor
  4. To keep both circuits at the same temperature

Explanation

A cascade system links two circuits through a heat exchanger so each refrigerant works over a narrower temperature and pressure range. This avoids excessively high pressure ratios and lets each circuit use a refrigerant suited to its temperature band. It is common in very low-temperature applications.

Question 18Refrigeration Fundamentals

What does the term 'flash gas' refer to in a refrigeration system?

  1. Vapour produced by boiling in the condenser
  2. Vapour formed when liquid refrigerant pressure is reduced through the expansion valve Correct answer.
  3. Gas released from the compressor during maintenance
  4. Air entering the system through a leaking seal

Explanation

When liquid refrigerant passes through the expansion valve, its pressure drops and part of the liquid flashes into vapour. This flash gas cools the remaining liquid to the evaporating temperature. The vapour portion does not contribute to useful cooling in the evaporator.

Question 19Refrigeration Fundamentals

Which of the following is a non-condensable gas that commonly causes high discharge pressure when it accumulates in a refrigeration system?

  1. Air Correct answer.
  2. Carbon dioxide
  3. Water vapour
  4. Nitrogen

Explanation

Air drawn in through poor evacuation or leaks collects in the condenser because it cannot condense at normal operating temperatures. It raises the discharge pressure and reduces efficiency. Non-condensables must be purged after proper evacuation.

Question 20Refrigeration Fundamentals

A technician measures a suction pressure corresponding to a saturation temperature of −10 °C and a suction line temperature of −2 °C. What is the superheat?

  1. 2 K
  2. −8 K
  3. 12 K
  4. 8 K Correct answer.

Explanation

Superheat is the suction line temperature minus the saturation temperature at suction pressure. Here −2 °C minus −10 °C gives 8 K of superheat. This confirms that the vapour is above its saturation point at the measured pressure.

Question 21Refrigeration Fundamentals

What is the main reason for using a liquid line filter-drier?

  1. To separate oil from the discharge gas
  2. To reduce the condensing pressure
  3. To remove moisture and solid particles from the liquid refrigerant Correct answer.
  4. To increase the refrigerant flow rate to the evaporator

Explanation

A filter-drier traps solid contaminants and absorbs moisture from the liquid line. Removing moisture prevents ice blockage at the expansion valve and acid formation in the system. Clean, dry refrigerant protects the compressor and valves.

Question 22Refrigeration Fundamentals

Which of the following best describes the coefficient of performance (COP) of a refrigeration cycle?

  1. Compressor work input divided by the refrigerating effect
  2. Refrigerating effect divided by the compressor work input Correct answer.
  3. Total heat absorbed divided by the total heat rejected
  4. Heat rejected in the condenser divided by the compressor work

Explanation

COP is defined as the useful cooling obtained divided by the work supplied to the compressor. A higher COP means more cooling per unit of energy consumed. It is the standard measure of refrigeration efficiency.

Question 23Refrigeration Fundamentals

Why must a refrigeration system be evacuated before charging with refrigerant?

  1. To increase the refrigerant charge required
  2. To warm the compressor before start-up
  3. To remove air and moisture that would otherwise cause high pressure and contamination Correct answer.
  4. To test the compressor motor winding resistance

Explanation

Evacuation with a vacuum pump removes air and moisture from the system. Left in place, air raises discharge pressure and moisture can freeze at the expansion valve or form acids that damage the compressor. A deep vacuum also confirms the system is leak-free.

Question 24Refrigeration Fundamentals

A refrigeration cycle has an evaporating temperature of −5 °C and a condensing temperature of 35 °C. What is the approximate pressure ratio if the refrigerant saturation pressures at these temperatures are 2.4 bar and 9.0 bar respectively?

  1. About 6.6
  2. About 0.27
  3. About 3.75 Correct answer.
  4. About 11.4

Explanation

The pressure ratio is the absolute discharge pressure divided by the absolute suction pressure, which here is 9.0 divided by 2.4, giving about 3.75. A higher ratio means greater compressor work per unit of cooling. Keeping the ratio moderate improves efficiency.

Question 25Refrigeration Fundamentals

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

  1. To cool the discharge gas before condensation
  2. To increase the superheat signal to the expansion valve
  3. To prevent liquid refrigerant from reaching the compressor by trapping it in the suction line Correct answer.
  4. To store high-pressure liquid after the condenser

Explanation

An accumulator is fitted in the suction line to catch any liquid refrigerant that leaves the evaporator and allow it to boil off. This protects the compressor from slugging. It is especially useful in systems where load varies widely.

Question 26Refrigeration Fundamentals

Which refrigerant property is defined as the ratio of the mass of water vapour in the air to the mass of dry air in the same sample?

  1. Relative humidity
  2. Absolute humidity
  3. Dew-point depression
  4. Specific humidity Correct answer.

Explanation

Specific humidity compares the mass of water vapour to the mass of dry air in a given sample, so it is a mass-to-mass ratio expressed in kg water per kg dry air. Relative humidity instead compares the actual vapour pressure to the saturation pressure at the same temperature. Absolute humidity measures vapour mass per unit volume of mixture.

Question 27Refrigeration Fundamentals

In a vapour-compression system, what is the primary effect of an increase in condensing pressure while evaporating pressure stays constant?

  1. The mass flow through the expansion device falls to zero
  2. The refrigerating effect per kilogram of refrigerant increases
  3. The compressor pressure ratio increases and the work of compression rises Correct answer.
  4. The evaporator superheat becomes zero

Explanation

Raising the condensing pressure widens the pressure difference the compressor must overcome, so the pressure ratio and the specific work of compression both increase. The refrigerating effect per kilogram is governed mainly by the evaporator, which is unchanged. The expansion device still passes flow, so mass flow does not fall to zero.

Question 28Refrigeration Fundamentals

Which statement correctly describes the role of the compressor in a vapour-compression refrigeration cycle?

  1. It raises the pressure of the vapour so that it can be condensed at a higher temperature Correct answer.
  2. It lowers the boiling point of the liquid refrigerant before it enters the evaporator
  3. It controls the amount of liquid refrigerant admitted to the evaporator
  4. It removes heat from the refrigerant vapour before it enters the condenser

Explanation

The compressor takes low-pressure vapour from the evaporator and raises its pressure, which also raises its saturation temperature so that heat can be rejected to the surroundings in the condenser. It does not itself remove heat from the refrigerant. Metering of liquid to the evaporator is the job of the expansion device.

Question 29Refrigeration Fundamentals

A room has a dry-bulb temperature of 30 °C and a wet-bulb temperature of 22 °C. What does the difference between these two readings indicate?

  1. The air can absorb moisture, since it is not saturated Correct answer.
  2. The air is fully saturated with water vapour
  3. The air is colder than the wet-bulb thermometer shows
  4. The air contains no water vapour at all

Explanation

A wet-bulb temperature below the dry-bulb temperature shows that evaporation from the wet bulb is cooling it, which happens only when the air is unsaturated. The greater the difference, the greater the drying capacity of the air. When the two readings are equal, the air is saturated.

Question 30Refrigeration Fundamentals

Which of the following best describes the state of the refrigerant at the outlet of an ideal evaporator?

  1. Superheated vapour
  2. Subcooled liquid
  3. Saturated vapour Correct answer.
  4. Saturated liquid

Explanation

In an ideal evaporator the refrigerant absorbs latent heat until it has just completely vaporised, leaving the coil as saturated vapour. Any further heating beyond that point produces superheat, which is avoided in the ideal case. Subcooled liquid and saturated liquid belong to the condenser outlet and expansion valve inlet.

Question 31Refrigeration Fundamentals

A refrigerant leaves the condenser as saturated liquid at 40 °C and is then cooled in the liquid line to 35 °C at the same pressure. What is this condition called and what is its value?

  1. Superheat of 5 K
  2. Subcooling of 5 K Correct answer.
  3. Subcooling of 40 K
  4. Superheat of 35 K

Explanation

Subcooling is the amount by which a liquid is cooled below its saturation temperature at the existing pressure. Here the saturation temperature is 40 °C and the liquid is at 35 °C, so the subcooling is 5 K. Superheat applies to vapour above its saturation temperature, not to liquid.

Question 32Refrigeration Fundamentals

Why does a refrigeration system with a capillary tube have no receiver or liquid line sight glass?

  1. The capillary tube stores the whole charge and the system is critically charged Correct answer.
  2. The charge is so large that a receiver would be unnecessary
  3. The refrigerant never changes phase in such systems
  4. The system operates without a condenser

Explanation

Capillary tube systems are charged with a precisely measured amount of refrigerant and have no receiver, so the charge is critical and a sight glass would serve no purpose. The small tube itself meters the flow and equalises pressure when the compressor stops. The refrigerant still condenses and evaporates as in any vapour-compression cycle.

Question 33Refrigeration Fundamentals

Which pressure-enthalpy process represents the expansion device in an ideal vapour-compression cycle?

  1. A constant-pressure compression
  2. A constant-enthalpy expansion Correct answer.
  3. A constant-temperature condensation
  4. A constant-entropy compression

Explanation

In the ideal cycle the expansion through a capillary tube or valve is treated as adiabatic and doing no work, so enthalpy stays constant while pressure and temperature fall. Compression is the constant-entropy process, and condensation occurs at constant pressure. The expansion is therefore drawn as a vertical line on a pressure-enthalpy diagram.

Question 34Refrigeration Fundamentals

A technician finds frost forming only at the inlet of an evaporator while the rest of the coil stays warm. Which fault best explains this pattern?

  1. The system is overcharged with refrigerant
  2. The compressor is oversized for the load
  3. The condenser fan is running too fast
  4. The expansion valve is admitting too little refrigerant Correct answer.

Explanation

An expansion valve that is underfeeding starves the coil, so refrigerant boils off early and the remaining coil surface receives little or no liquid to evaporate. The cold inlet frosts while downstream sections stay warm. Overcharging would tend to flood the coil and frost it more evenly.

Question 35Refrigeration Fundamentals

Which of the following is the standard saturation temperature of refrigerant R-22 at atmospheric pressure?

  1. −40.8 °C Correct answer.
  2. −26.1 °C
  3. −10.0 °C
  4. +4.4 °C

Explanation

R-22 boils at approximately −40.8 °C at standard atmospheric pressure, which is why it was widely used in low-temperature applications. This value is a fixed physical property of the refrigerant. The other figures correspond to different refrigerants or to arbitrary operating conditions.

Question 36Refrigeration Fundamentals

What is the function of the oil separator fitted on the discharge line of a large reciprocating compressor?

  1. It reduces the discharge pressure before the condenser
  2. It removes moisture from the refrigerant
  3. It removes entrained oil from the hot gas so oil returns to the crankcase Correct answer.
  4. It removes non-condensable gases from the system

Explanation

Oil carried out of the compressor in the discharge gas can coat evaporator surfaces and reduce heat transfer, so an oil separator traps it and returns it to the crankcase. It works by changing the direction and velocity of the gas so droplets settle out. Moisture removal is the task of the filter-drier.

Question 37Refrigeration Fundamentals

In a direct expansion (DX) coil, what does the term 'direct expansion' indicate?

  1. Air is cooled by evaporating water sprayed over the coil
  2. Refrigerant evaporates directly inside the coil that cools the air Correct answer.
  3. Chilled water is circulated through the coil to cool the air
  4. The coil is defrosted by reversing the refrigerant flow

Explanation

In a DX coil the refrigerant itself expands and evaporates inside the tubes, absorbing heat directly from the air passing over the fins. This differs from a chilled-water coil, where a secondary fluid carries the cooling. The absence of a secondary loop is the defining feature of direct expansion.

Question 38Refrigeration Fundamentals

A refrigeration plant rejects 15 kW at the condenser while absorbing 10 kW at the evaporator. What is the approximate coefficient of performance of the cycle?

  1. 1.50
  2. 2.00 Correct answer.
  3. 2.50
  4. 0.67

Explanation

The coefficient of performance is the refrigerating effect divided by the compressor work input. The work equals condenser heat rejected minus evaporator heat absorbed, which is 15 − 10 = 5 kW, so COP = 10 / 5 = 2.0. Using the wrong ratio of the two heat quantities gives the incorrect distractors.

Question 39Refrigeration Fundamentals

Why does a two-stage compression system with intercooling improve performance at very low evaporating temperatures?

  1. It reduces the total compressor work by avoiding an excessive pressure ratio in one stage Correct answer.
  2. It allows the use of a larger expansion valve
  3. It eliminates the need for a condenser
  4. It removes the need for any refrigerant charge

Explanation

At very low evaporating temperatures a single compressor would face a very high pressure ratio, which raises discharge temperature and lowers volumetric efficiency. Splitting compression into two stages with intercooling reduces the work per stage and keeps discharge temperatures manageable. A condenser is still required in every vapour-compression system.

Question 40Refrigeration Fundamentals

Which of the following instruments is used to measure the relative humidity of air in an air-conditioned space?

  1. Barometer
  2. Manometer
  3. Anemometer
  4. Hygrometer Correct answer.

Explanation

A hygrometer measures the moisture content or relative humidity of air, using principles such as wet- and dry-bulb temperatures or a capacitive sensor. A manometer measures pressure difference and an anemometer measures air velocity. A barometer measures atmospheric pressure.

Question 41Refrigeration Systems and Components

What is the primary function of the expansion valve in a refrigeration system?

  1. To meter refrigerant flow and reduce pressure from condensing to evaporating level Correct answer.
  2. To remove moisture from the refrigerant liquid
  3. To store excess refrigerant during low load
  4. To increase the refrigerant pressure before compression

Explanation

The expansion device throttles liquid refrigerant, dropping its pressure and temperature so it can evaporate and absorb heat in the evaporator. It also regulates the mass flow to match the evaporator load. Pressure rise and moisture removal are handled by other components.

Question 42Refrigeration Systems and Components

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

  1. R-134a Correct answer.
  2. R-290 (propane)
  3. R-717 (ammonia)
  4. R-1234yf

Explanation

A1 refrigerants have low toxicity and no flame propagation; R-134a falls in this class. Ammonia is B2 because of its toxicity, while propane and R-1234yf are flammable and therefore classed A3 or A2L respectively. The letter gives toxicity and the number gives flammability.

Question 43Refrigeration Systems and Components

A refrigerant leaves the evaporator at a temperature above its saturation temperature at the evaporator pressure. What is this condition called?

  1. Superheat Correct answer.
  2. Desuperheating
  3. Subcooling
  4. Flash gas

Explanation

Superheat is the number of degrees a vapour is above its saturation temperature at the given pressure. It confirms that no liquid remains to reach the compressor. Subcooling is the opposite condition for a liquid, and flash gas is vapour formed during throttling.

Question 44Refrigeration Systems and Components

What is the purpose of the receiver in a system using a thermostatic expansion valve?

  1. To hold liquid refrigerant and ensure a solid liquid seal at the valve inlet Correct answer.
  2. To cool the compressor discharge gas
  3. To raise the suction pressure during defrost
  4. To separate oil from the refrigerant vapour

Explanation

The receiver stores liquid refrigerant and keeps the liquid line full so the expansion valve receives bubble-free liquid. Vapour entering the valve would reduce capacity and cause erratic control. Oil separation and discharge cooling are functions of other components.

Question 45Refrigeration Systems and Components

Which type of compressor is most commonly used in large industrial ammonia refrigeration plants?

  1. Hermetic scroll compressor
  2. Rotary vane compressor
  3. Centrifugal compressor
  4. Reciprocating open compressor Correct answer.

Explanation

Open reciprocating compressors are widely used with ammonia because they tolerate high discharge temperatures and allow shaft seals and bearings to be serviced independently of the motor. Hermetic designs are unsuitable because ammonia attacks copper motor windings. Scroll and rotary types are mainly used in small halocarbon systems.

Question 46Refrigeration Systems and Components

What does the term 'approach' refer to in a cooling tower?

  1. The pressure drop across the fill
  2. The difference between the entering water temperature and the dry-bulb temperature
  3. The ratio of make-up water to circulating water
  4. The difference between the leaving water temperature and the entering air wet-bulb temperature Correct answer.

Explanation

Cooling tower approach is the gap between the cold water leaving the tower and the ambient wet-bulb temperature. It indicates how closely the tower performs to the theoretical limit set by evaporation. Range, by contrast, is the drop between hot and cold water temperatures.

Question 47Refrigeration Systems and Components

Which component protects the compressor by stopping the motor when the oil pressure is too low?

  1. The low-pressure cut-out
  2. The suction line accumulator
  3. The oil pressure safety switch Correct answer.
  4. The high-pressure cut-out

Explanation

An oil pressure safety switch senses the net oil pressure and opens the control circuit if adequate pressure is not established within a set delay. This prevents bearing damage from inadequate lubrication. High and low pressure cut-outs respond to refrigerant pressures, not oil pressure.

Question 48Refrigeration Systems and Components

A technician measures a suction line superheat of 2 K at the compressor inlet on an R-134a system with a thermostatic expansion valve. What does this most likely indicate?

  1. The valve is overfeeding and liquid may reach the compressor Correct answer.
  2. The system is correctly charged
  3. The condenser is fouled
  4. The refrigerant charge is low

Explanation

Normal superheat at the compressor is typically 5 to 10 K; 2 K is too low and suggests the valve is passing too much refrigerant. The risk is liquid slugging, which can damage compressor valves. A low charge would raise superheat, not lower it.

Question 49Refrigeration Systems and Components

What happens to the refrigerating effect per kilogram of refrigerant if the evaporating temperature is lowered while the condensing temperature stays constant?

  1. It doubles because the compressor speed is unchanged
  2. It stays the same because only mass flow changes
  3. It increases because the latent heat of vaporisation rises
  4. It decreases because the pressure ratio and flash gas increase Correct answer.

Explanation

A lower evaporating temperature widens the pressure ratio and increases the proportion of flash gas formed during throttling. Less of each kilogram evaporates usefully in the evaporator, so the refrigerating effect per kilogram falls and capacity drops. Power per unit of cooling also rises.

Question 50Refrigeration Systems and Components

Why is a suction line accumulator fitted in some refrigeration systems?

  1. To store liquid refrigerant during the off cycle and prevent it reaching the compressor Correct answer.
  2. To remove non-condensable gases
  3. To subcool the liquid line
  4. To increase the discharge pressure

Explanation

An accumulator traps liquid refrigerant that may flood back from the evaporator and meters it back as vapour. This protects the compressor from slugging during load changes or defrost. It does not affect discharge pressure or liquid subcooling.