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NATE Core practice questions

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Question 1Core (HVACR fundamentals)

A technician measures the temperature of a refrigerant line at 40°F using a digital thermometer. Which type of temperature measurement does this represent?

  1. Dew point temperature
  2. Wet-bulb temperature
  3. Saturation temperature
  4. Dry-bulb temperature Correct answer.

Explanation

Dry-bulb temperature is the actual sensible temperature of the air or surface as read by a standard thermometer, unaffected by moisture content. Wet-bulb accounts for evaporative cooling, dew point marks the moisture condensation threshold, and saturation temperature is tied to refrigerant pressure.

Question 2Core (HVACR fundamentals)

Which instrument is used to measure the electrical resistance of a compressor motor winding?

  1. Anemometer
  2. Ohmmeter Correct answer.
  3. Manometer
  4. Clamp meter

Explanation

An ohmmeter measures resistance in ohms and is used to check winding continuity and balance. A clamp meter measures current, a manometer measures pressure, and an anemometer measures air velocity.

Question 3Core (HVACR fundamentals)

What is the primary function of the condenser in a vapor-compression refrigeration system?

  1. Increase refrigerant pressure before the evaporator
  2. Absorb heat from the conditioned space
  3. Reject heat from the refrigerant to the surroundings Correct answer.
  4. Meter refrigerant flow to the evaporator

Explanation

The condenser rejects heat absorbed by the refrigerant to the outdoor air or water, causing the refrigerant to condense from vapor to liquid. The evaporator absorbs heat, the metering device regulates flow, and the compressor raises pressure.

Question 4Core (HVACR fundamentals)

In a refrigerant piping system, what does the term 'subcooling' describe?

  1. Liquid refrigerant cooled below its saturation temperature at a given pressure Correct answer.
  2. The pressure drop across the metering device
  3. The temperature difference across the evaporator coil
  4. Vapor refrigerant heated above its saturation temperature

Explanation

Subcooling is the amount by which liquid refrigerant is cooled below its saturation temperature for the existing pressure, confirming a solid liquid column at the condenser outlet. Superheat, by contrast, describes vapor above saturation.

Question 5Core (HVACR fundamentals)

A technician needs to check the pressure of refrigerant in a sealed system. Which tool is appropriate?

  1. Manifold gauge set Correct answer.
  2. Hygrometer
  3. Vacuum gauge
  4. Multimeter

Explanation

A manifold gauge set reads both high-side and low-side refrigerant pressures and connects to service ports. Vacuum gauges measure deep vacuum during evacuation, multimeters measure electrical values, and hygrometers measure humidity.

Question 6Core (HVACR fundamentals)

Which safety practice is required before working on a rooftop unit's electrical panel?

  1. Lock out and tag out the disconnect Correct answer.
  2. Install a new filter in the return
  3. Increase the thermostat setpoint
  4. Open the refrigerant service valves

Explanation

Lockout/tagout isolates the energy source and prevents accidental energization while the technician works on electrical components. The other steps do not remove electrical hazards.

Question 7Core (HVACR fundamentals)

What does a refrigerant's 'saturation temperature' represent?

  1. The temperature of the refrigerant at the compressor discharge
  2. The temperature at which liquid and vapor coexist at a given pressure Correct answer.
  3. The temperature at which the refrigerant is entirely superheated
  4. The temperature at which the refrigerant freezes solid

Explanation

Saturation temperature is the boiling or condensing temperature for a specific refrigerant at a specific pressure; at that point liquid and vapor coexist. It is read from a pressure-temperature chart.

Question 8Core (HVACR fundamentals)

Which type of heat transfer occurs when heat moves through the copper wall of a refrigerant tube?

  1. Convection
  2. Conduction Correct answer.
  3. Radiation
  4. Evaporation

Explanation

Conduction is heat transfer through a solid material by molecular contact, such as through a tube wall. Convection involves fluid movement, radiation is electromagnetic, and evaporation is a phase change.

Question 9Core (HVACR fundamentals)

A technician reads a low-side pressure of 60 psig on an R-410A system. Using a pressure-temperature chart, what does this pressure indicate about the evaporator saturation temperature?

  1. Approximately 60°F
  2. Approximately 100°F
  3. Approximately 35°F Correct answer.
  4. Approximately 10°F

Explanation

On an R-410A pressure-temperature chart, 60 psig corresponds to a saturation temperature near 35°F. The technician then compares this to the measured suction line temperature to determine superheat.

Question 10Core (HVACR fundamentals)

A technician measures a suction line temperature of 55°F and an evaporator saturation temperature of 40°F. What is the superheat?

  1. 40°F
  2. 55°F
  3. 15°F Correct answer.
  4. 95°F

Explanation

Superheat equals the suction line temperature minus the evaporator saturation temperature, so 55°F − 40°F = 15°F. This value confirms the refrigerant is fully vaporized before the compressor.

Question 11Core (HVACR fundamentals)

Why must refrigerant lines be properly insulated on the suction side?

  1. To raise the condenser saturation temperature
  2. To increase the refrigerant pressure
  3. To reduce the compressor's electrical draw
  4. To prevent heat gain and condensation on the line Correct answer.

Explanation

Insulation on the suction line limits heat gain into cold refrigerant and prevents condensation or frost on the line. It does not change system pressures or compressor draw directly.

Question 12Core (HVACR fundamentals)

A technician observes that a compressor motor winding shows infinite resistance between the common terminal and the run terminal. What does this indicate?

  1. The winding is open Correct answer.
  2. The winding is shorted
  3. The capacitor is weak
  4. The winding is properly balanced

Explanation

Infinite resistance on a winding indicates an open circuit, meaning the winding is broken and the motor will not run. A short would show near-zero resistance, and a balanced winding would show a specific expected value.

Question 13Core (HVACR fundamentals)

What is the purpose of the metering device in a refrigeration system?

  1. To raise refrigerant pressure entering the condenser
  2. To reduce pressure and control refrigerant flow into the evaporator Correct answer.
  3. To filter moisture from the refrigerant
  4. To store excess refrigerant during low load

Explanation

The metering device drops refrigerant pressure and regulates flow so the evaporator can boil refrigerant at the desired low temperature. It is the dividing point between high and low sides.

Question 14Core (HVACR fundamentals)

A technician is evacuating a system and reads 500 microns on a vacuum gauge. What does this reading indicate?

  1. The system has reached a deep vacuum suitable for charging Correct answer.
  2. The vacuum pump is operating normally but the system is full of air
  3. The system still contains significant moisture or leaks
  4. The system is overcharged with refrigerant

Explanation

A reading of 500 microns or lower indicates a deep vacuum, confirming that air and moisture have been removed and the system can be charged. Higher micron readings indicate residual moisture or leaks.

Question 15Core (HVACR fundamentals)

What is the function of a filter drier in a refrigeration system?

  1. To remove moisture and contaminants from the refrigerant Correct answer.
  2. To store liquid refrigerant for the condenser
  3. To measure refrigerant pressure
  4. To regulate refrigerant flow to the evaporator

Explanation

A filter drier removes moisture, acid, and particulate contaminants from the refrigerant stream to protect the compressor and metering device. It does not regulate flow or store refrigerant.

Question 16Core (HVACR fundamentals)

A technician is troubleshooting a system with a high suction pressure and a low superheat. Which condition is most likely?

  1. Overcharge of refrigerant or an overfeeding metering device Correct answer.
  2. Undercharge of refrigerant
  3. A restricted liquid line
  4. A failed condenser fan

Explanation

High suction pressure combined with low superheat suggests excess refrigerant reaching the evaporator, often from overcharge or an overfeeding metering device. Undercharge and restrictions typically produce low suction pressure and high superheat.

Question 17Core (HVACR fundamentals)

What does the term 'delta-T' refer to when checking an air-conditioning system?

  1. The difference between high-side and low-side pressures
  2. The difference between supply and return air temperatures Correct answer.
  3. The difference between indoor and outdoor temperatures
  4. The difference between compressor amp draw and rated amps

Explanation

Delta-T is the temperature difference between the return air entering the evaporator and the supply air leaving it, used to verify airflow and coil performance. A typical range is roughly 15°F to 22°F.

Question 18Core (HVACR fundamentals)

Which of the following best describes sensible heat?

  1. Heat that causes a phase change without a temperature change
  2. Heat that changes the temperature of a substance without a phase change Correct answer.
  3. Heat rejected by the condenser coil
  4. Heat absorbed only by water vapor

Explanation

Sensible heat changes the temperature of a substance and can be sensed by a thermometer. Latent heat, by contrast, causes a phase change at constant temperature.

Question 19Core (HVACR fundamentals)

A technician measures the compressor amp draw and compares it to the nameplate rated load amps. The measured value is significantly higher than the rated value. What is a likely cause?

  1. A failing run capacitor or mechanical binding Correct answer.
  2. A loose thermostat wire
  3. A clogged air filter only
  4. Low refrigerant charge

Explanation

Excessive amp draw relative to rated load amps often points to a failing capacitor, a seized bearing, or mechanical binding that increases motor load. Low charge and airflow issues typically reduce amp draw.

Question 20Core (HVACR fundamentals)

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

  1. To warm the compressor oil and prevent refrigerant migration during the off cycle Correct answer.
  2. To increase evaporator superheat
  3. To raise the discharge temperature during operation
  4. To reduce the compressor's current draw

Explanation

A crankcase heater keeps the compressor oil warm during the off cycle so refrigerant does not migrate into the crankcase and dilute the oil. This protects the compressor at startup.

Question 21Core (HVACR fundamentals)

A technician is charging a system using the superheat method. Which measurement combination is required?

  1. Suction line temperature and evaporator saturation temperature Correct answer.
  2. Discharge pressure and compressor amp draw
  3. Liquid line temperature and condenser saturation temperature
  4. Return air temperature and supply air temperature

Explanation

The superheat method uses suction line temperature minus evaporator saturation temperature to determine proper charge for fixed-orifice systems. Subcooling uses liquid line and condenser saturation temperatures.

Question 22Core (HVACR fundamentals)

A technician finds that a system has a low suction pressure, high superheat, and a frosted suction line. Which condition is most consistent with these readings?

  1. A failed condenser fan motor
  2. A stuck-open metering device
  3. A restricted liquid line or undercharge Correct answer.
  4. An overcharge of refrigerant

Explanation

Low suction pressure with high superheat and frost suggests the evaporator is starved of refrigerant due to a restriction or undercharge. Overcharge and overfeeding produce the opposite pattern.

Question 23Core (HVACR fundamentals)

Which of the following best explains why non-condensable gases in a refrigeration system are harmful?

  1. They lower the compressor's amp draw
  2. They increase evaporator superheat predictably
  3. They improve condenser heat rejection
  4. They raise head pressure and reduce system efficiency Correct answer.

Explanation

Non-condensable gases such as air collect in the condenser, raising head pressure and reducing efficiency while increasing compressor load. They are removed by proper evacuation.

Question 24Core (HVACR fundamentals)

A technician is diagnosing a system where the compressor runs continuously but the space never reaches the setpoint. The suction pressure is normal, but the supply air delta-T is only 6°F. What is the most likely cause?

  1. A refrigerant overcharge
  2. Excessive airflow across the evaporator or a dirty blower Correct answer.
  3. A failed compressor valve
  4. A restricted metering device

Explanation

A low delta-T with normal suction pressure points to excessive airflow or poor heat exchange, such as a dirty blower or oversized airflow, rather than a refrigerant problem. The air is moving too fast to be properly cooled.

Question 25Core (HVACR fundamentals)

What is the significance of the pressure-enthalpy diagram in refrigeration analysis?

  1. It shows the moisture content of the refrigerant
  2. It shows the relationship between refrigerant pressure and enthalpy through each cycle stage Correct answer.
  3. It shows the relationship between voltage and current in the compressor
  4. It shows the airflow across the evaporator coil

Explanation

A pressure-enthalpy diagram plots refrigerant pressure against enthalpy, allowing technicians to trace each cycle stage and calculate capacity and efficiency. It is a thermodynamic tool, not an electrical or airflow chart.

Question 26Core (HVACR fundamentals)

A technician is preparing to braze a copper refrigerant line and wants to prevent oxidation inside the tubing. What practice is recommended?

  1. Flush the line with compressed air before heating
  2. Coat the inside of the tubing with brazing flux
  3. Cap both ends of the tubing to trap air inside
  4. Purge the line with dry nitrogen while brazing Correct answer.

Explanation

Flowing dry nitrogen through the tubing during brazing displaces oxygen so copper oxide scale cannot form on the inside surface. Oxide flakes later migrate to the metering device and compressor and cause restrictions and wear. Flux is not used inside refrigerant piping, and trapped air promotes scale formation.

Question 27Core (HVACR fundamentals)

Which instrument is used to measure the relative humidity of air entering an evaporator coil?

  1. Vacuum micron gauge
  2. Clamp-on ammeter
  3. Manometer
  4. Sling psychrometer Correct answer.

Explanation

A sling psychrometer measures dry-bulb and wet-bulb temperatures, and the two readings are used to determine relative humidity and dew point. Manometers measure pressure, ammeters measure current, and micron gauges measure deep vacuum, so none of them directly indicates humidity.

Question 28Core (HVACR fundamentals)

Why must refrigerant suction lines be properly insulated?

  1. To keep the refrigerant pressure from rising above the design limit
  2. To reduce the noise produced by refrigerant flow
  3. To prevent heat gain that would increase superheat and reduce capacity Correct answer.
  4. To prevent the line from rusting through condensation

Explanation

The suction line carries cold vapor, and without insulation ambient heat enters the refrigerant and raises its temperature. That added heat increases superheat, expands the vapor, and lowers the mass flow and capacity of the system. Insulation also limits condensation, but capacity loss is the primary refrigeration concern.

Question 29Core (HVACR fundamentals)

A technician measures the compressor amp draw and compares it to the nameplate rated load amps. The measured value is significantly above the rated load amps. What condition does this most likely indicate?

  1. The compressor is running with a low refrigerant charge
  2. The compressor is operating normally at part load
  3. The compressor is being supplied with low voltage and should draw less current
  4. The compressor is drawing excessive current because of a mechanical or electrical problem Correct answer.

Explanation

Current above the rated load amps indicates the compressor is working harder than its design condition, often from a failing bearing, a shorted winding, or abnormally high head pressure. The technician should check voltage, refrigerant pressures, and winding resistance before condemning the compressor. Continued operation at excessive current risks tripping the overload or damaging the motor.

Question 30Core (HVACR fundamentals)

A technician is charging a fixed-orifice system using the superheat method. Which measurement combination is required?

  1. Suction pressure converted to saturation temperature plus suction line temperature Correct answer.
  2. Liquid line pressure converted to saturation temperature plus liquid line temperature
  3. Discharge pressure plus outdoor ambient temperature
  4. Suction pressure plus compressor amp draw

Explanation

Superheat charging requires the low-side pressure, which is converted to evaporator saturation temperature, and the suction line temperature. Subtracting saturation temperature from line temperature gives superheat, which is compared with the manufacturer's target. This method is used on fixed-orifice systems because the orifice cannot adjust flow.

Question 31Core (HVACR fundamentals)

A technician finds that a system has a low suction pressure, high superheat, and a frosted suction line. Which condition is most likely?

  1. An overcharge of refrigerant
  2. A dirty condenser coil
  3. A restriction in the liquid line or a clogged metering device Correct answer.
  4. An oversized evaporator coil

Explanation

Low suction pressure with high superheat and frost on the suction line indicates the evaporator is starved of refrigerant. A restriction, such as a clogged filter drier or a stuck metering device, limits flow and causes the refrigerant to boil off early. The frost forms because the low pressure drives the coil temperature below freezing.

Question 32Core (HVACR fundamentals)

A technician observes that a compressor motor winding shows infinite resistance between the common terminal and the run terminal. What does this reading most likely indicate?

  1. A normal reading for a single-phase compressor
  2. A grounded start winding
  3. An open winding in the run circuit Correct answer.
  4. A shorted run winding to ground

Explanation

Infinite resistance between common and run means there is no continuous electrical path through the run winding, which indicates an open winding. A normal winding would show a measurable resistance in the range of a few ohms. The technician should also check the start-to-common and run-to-start resistances to confirm.

Question 33Core (HVACR fundamentals)

A technician is diagnosing a system where the compressor runs continuously but the space never reaches the setpoint. The suction pressure is normal and the superheat is normal. Which condition should the technician investigate next?

  1. A refrigerant overcharge
  2. A failed compressor run capacitor
  3. A restricted metering device
  4. Excessive building heat gain or a duct distribution problem Correct answer.

Explanation

Normal suction pressure and superheat indicate the refrigeration circuit is operating correctly, so the problem likely lies on the air side or in the load. Excessive heat gain, duct leakage, or poor air distribution can prevent the space from reaching setpoint even with a healthy system. The technician should check airflow, insulation, and building envelope.

Question 34Core (HVACR fundamentals)

A technician is checking a heat pump in heating mode and finds that the outdoor coil is frosted while the system is running. Which condition is most likely?

  1. The defrost control is not initiating a defrost cycle Correct answer.
  2. The reversing valve is stuck in the cooling position
  3. The refrigerant charge is significantly overcharged
  4. The indoor blower is running at too high a speed

Explanation

In heating mode, the outdoor coil is the evaporator and normally frosts, so the defrost control must periodically reverse the cycle or energize heaters to clear it. Continuous frost with no defrost suggests a failed sensor, timer, or defrost board. If the reversing valve were stuck in cooling, the outdoor coil would act as the condenser and would not frost.

Question 35Core (HVACR fundamentals)

A technician is preparing to work on a rooftop unit's electrical panel. Which safety practice is required before beginning?

  1. Lock out and tag out the disconnect and verify the circuit is de-energized Correct answer.
  2. Ask the building owner to switch off the breaker without locking it
  3. Turn the thermostat to the off position and begin work immediately
  4. Wear insulating gloves and work with one hand in the panel

Explanation

Lockout and tagout isolates the energy source and prevents accidental re-energization while the technician works. The technician must then verify the circuit is de-energized with a meter before touching conductors. Simply turning off a thermostat or asking someone to open a breaker does not provide a reliable safeguard.

Question 36Core (HVACR fundamentals)

A technician is evaluating a system with a low suction pressure, high superheat, and a frosted suction line. Which condition is most likely?

  1. A restriction in the liquid line or a clogged metering device Correct answer.
  2. An oversized evaporator coil
  3. An overcharge of refrigerant
  4. A dirty condenser coil

Explanation

Low suction pressure with high superheat and frost on the suction line indicates the evaporator is starved of refrigerant. A restriction, such as a clogged filter drier or a stuck metering device, limits flow and causes the refrigerant to boil off early. The frost forms because the low pressure drives the coil temperature below freezing.

Question 37Core (HVACR fundamentals)

In a refrigeration system, what is the primary function of the metering device?

  1. To increase refrigerant pressure before the condenser
  2. To regulate refrigerant flow and maintain the evaporator pressure differential Correct answer.
  3. To store excess refrigerant during low-load conditions
  4. To filter moisture and debris from the refrigerant

Explanation

The metering device controls the flow of refrigerant into the evaporator, creating a pressure drop that allows the refrigerant to boil at a low temperature and absorb heat. It does not increase pressure, filter, or store refrigerant.

Question 38Core (HVACR fundamentals)

Which component in a vapor-compression cycle is responsible for rejecting heat from the refrigerant to the outdoor air?

  1. Compressor
  2. Expansion valve
  3. Evaporator
  4. Condenser Correct answer.

Explanation

The condenser receives high-pressure, high-temperature vapor from the compressor and rejects heat to the surrounding air or water, causing the refrigerant to condense into a liquid. The evaporator absorbs heat, the compressor raises pressure and temperature, and the expansion valve reduces pressure.

Question 39Core (HVACR fundamentals)

What is the primary purpose of a filter-drier in a refrigeration system?

  1. To remove moisture and solid contaminants from the refrigerant Correct answer.
  2. To regulate the refrigerant flow to the evaporator
  3. To reduce compressor noise and vibration
  4. To increase refrigerant subcooling before the expansion valve

Explanation

A filter-drier contains a desiccant and a filter screen to trap moisture and solid particles that could cause acid formation, ice blockage, or component wear. It does not affect subcooling, flow regulation, or noise.

Question 40Core (HVACR fundamentals)

Which safety hazard is associated with refrigerant vapors in a confined space?

  1. They are corrosive to human skin at low concentrations
  2. They are always flammable at room temperature
  3. They can displace oxygen and cause asphyxiation Correct answer.
  4. They have a strong odor that serves as an adequate warning

Explanation

Many refrigerants are heavier than air and can accumulate in low areas, displacing oxygen and creating an asphyxiation risk. Most common refrigerants are not flammable at room temperature, are not corrosive at low concentrations, and may be odorless or have a faint odor that is not a reliable warning.

Question 41Core (HVACR fundamentals)

What does a manifold gauge set measure when connected to a refrigeration system?

  1. Refrigerant temperature and humidity
  2. Electrical current and voltage
  3. Airflow velocity and static pressure
  4. System pressures on the high and low sides Correct answer.

Explanation

A manifold gauge set is used to read the high-side (discharge) and low-side (suction) pressures of a refrigeration system. It does not directly measure temperature, humidity, electrical values, or airflow.

Question 42Core (HVACR fundamentals)

Which type of heat is added to or removed from a substance without causing a change in temperature?

  1. Radiant heat
  2. Specific heat
  3. Sensible heat
  4. Latent heat Correct answer.

Explanation

Latent heat is the energy absorbed or released during a phase change, such as boiling or condensing, and it does not produce a temperature change. Sensible heat causes a measurable temperature change, specific heat is a material property, and radiant heat is a mode of heat transfer.

Question 43Core (HVACR fundamentals)

What is the primary function of the compressor in a vapor-compression refrigeration cycle?

  1. To raise the pressure and temperature of the refrigerant vapor Correct answer.
  2. To condense the refrigerant into a liquid
  3. To absorb heat from the conditioned space
  4. To control the flow of refrigerant into the evaporator

Explanation

The compressor draws low-pressure vapor from the evaporator and compresses it, increasing both its pressure and temperature so that it can reject heat in the condenser. It does not absorb heat, condense refrigerant, or regulate flow.

Question 44Core (HVACR fundamentals)

Which of the following is a correct safety practice when working with refrigerant cylinders?

  1. Secure cylinders upright and protect them from physical damage Correct answer.
  2. Use cylinders as a workbench for tools when not in use
  3. Fill cylinders completely to maximize refrigerant capacity
  4. Store cylinders in a horizontal position to save space

Explanation

Refrigerant cylinders should always be stored upright and secured to prevent tipping, and they should be protected from damage. They should never be laid horizontally, overfilled, or used as a work surface.

Question 45Core (HVACR fundamentals)

A technician is troubleshooting a system and finds that the evaporator coil is iced over while the system is running. Which of the following is the most likely cause?

  1. Overcharge of refrigerant
  2. High outdoor ambient temperature
  3. Restricted airflow across the evaporator Correct answer.
  4. Failed condenser fan motor

Explanation

Restricted airflow across the evaporator reduces the heat load on the coil, causing the refrigerant to boil at a lower pressure and temperature, which leads to frosting and icing. Overcharge, condenser fan failure, and high ambient temperature would typically increase pressures and reduce the likelihood of icing.

Question 46Core (HVACR fundamentals)

A technician measures a temperature difference of 8°F across the evaporator coil. What does this indicate?

  1. The compressor is not running
  2. The evaporator coil is completely blocked
  3. The system is overcharged with refrigerant
  4. The system is operating within a typical range for many systems Correct answer.

Explanation

A temperature difference (delta-T) across the evaporator coil of about 8°F to 12°F is often considered normal for many air-conditioning systems, indicating proper heat absorption. A significantly lower delta-T could indicate low charge or airflow issues, while a much higher delta-T could indicate low airflow.

Question 47Core (HVACR fundamentals)

Which of the following best describes the function of a thermostatic expansion valve (TXV)?

  1. It adjusts the condenser fan speed based on ambient temperature
  2. It maintains a constant evaporator pressure regardless of load
  3. It controls the compressor cycling to maintain room temperature
  4. It regulates refrigerant flow to maintain a constant superheat at the evaporator outlet Correct answer.

Explanation

A TXV modulates refrigerant flow in response to the superheat at the evaporator outlet, using a sensing bulb to maintain a constant superheat. It does not maintain constant evaporator pressure, cycle the compressor, or control condenser fans.

Question 48Core (HVACR fundamentals)

A technician is diagnosing a system with a high suction pressure and a low superheat. Which condition is most likely?

  1. Restricted liquid line
  2. Low refrigerant charge
  3. Overcharge of refrigerant Correct answer.
  4. Failed evaporator fan motor

Explanation

An overcharge of refrigerant increases the amount of liquid in the evaporator, leading to higher suction pressure and lower superheat, potentially causing liquid slugging. Low charge would cause low suction pressure and high superheat; a restricted liquid line would cause low suction pressure and high superheat; a failed evaporator fan would cause low suction pressure and high superheat.

Question 49Core (HVACR fundamentals)

What is the purpose of a condenser subcooling measurement?

  1. To check the compressor amp draw
  2. To verify the refrigerant charge and condenser performance Correct answer.
  3. To determine the evaporator airflow
  4. To measure the temperature rise across the evaporator

Explanation

Subcooling is the difference between the condensing temperature (from the high-side pressure) and the liquid line temperature. It indicates how much the refrigerant has been cooled below its condensing point and is used to verify charge and condenser operation. It does not measure airflow, amp draw, or evaporator temperature rise.

Question 50Core (HVACR fundamentals)

A technician is checking a heat pump in cooling mode and finds that the indoor coil is not removing humidity properly. Which of the following could be the cause?

  1. Defective outdoor fan motor
  2. Refrigerant undercharge
  3. Reversed reversing valve
  4. Too high indoor airflow Correct answer.

Explanation

Excessive indoor airflow reduces the temperature differential across the evaporator coil, resulting in less condensation and poor humidity removal. Undercharge, a reversed reversing valve, or a defective outdoor fan would typically cause other symptoms such as low suction pressure or high head pressure.