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NATE Heat Pump Service practice questions

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Question 1Heat Pump Fundamentals and System Components

In a vapor-compression heat pump, which component raises the refrigerant pressure and temperature from the evaporator level to the condenser level?

  1. The metering device
  2. The accumulator
  3. The reversing valve
  4. The compressor Correct answer.

Explanation

The compressor is the only component that adds work to the refrigerant, raising both its pressure and its saturation temperature so heat can be rejected in the condenser. All other listed components either route, throttle, or store refrigerant without adding compression work.

Question 2Heat Pump Fundamentals and System Components

A heat pump is operating in heating mode. Through which coil does the refrigerant absorb heat from the outdoor air?

  1. The outdoor coil Correct answer.
  2. The indoor coil
  3. The desuperheater coil
  4. The liquid-line filter drier

Explanation

In heating mode the reversing valve makes the outdoor coil the evaporator, so refrigerant absorbs heat from outdoor air there. The indoor coil becomes the condenser and rejects heat to the conditioned space.

Question 3Heat Pump Fundamentals and System Components

What is the primary function of the reversing valve in an air-source heat pump?

  1. To modulate compressor capacity in response to room load
  2. To maintain a constant superheat at the evaporator outlet
  3. To swap the roles of the indoor and outdoor coils between heating and cooling Correct answer.
  4. To bypass the metering device during defrost

Explanation

The reversing valve redirects discharge and suction gas so the coil that was the evaporator becomes the condenser and vice versa. This role swap is what allows one refrigerant circuit to provide both heating and cooling.

Question 4Heat Pump Fundamentals and System Components

Which metering device is most common on modern residential heat pumps because it maintains proper flow in both heating and cooling modes?

  1. A thermostatic expansion valve with a bidirectional or check-valve arrangement Correct answer.
  2. A hand expansion valve adjusted by the technician at each season change
  3. A fixed-bore orifice installed only in the liquid line
  4. A capillary tube with no bypass

Explanation

Heat pumps must meter refrigerant in two flow directions, so a thermostatic expansion valve with a check valve or a bidirectional balanced-port design is standard. It provides proper superheat control in both modes without manual adjustment.

Question 5Heat Pump Fundamentals and System Components

What does the term balance point mean when applied to an air-source heat pump?

  1. The temperature at which the defrost cycle terminates
  2. The point where indoor and outdoor coil pressures equalize during the off cycle
  3. The refrigerant pressure at which the reversing valve shifts
  4. The outdoor temperature at which heat pump capacity equals the building heat loss Correct answer.

Explanation

The balance point is the outdoor design temperature where the heat pump's heating capacity exactly matches the structure's heat loss. Below that point, supplemental heat is required to maintain indoor temperature.

Question 6Heat Pump Fundamentals and System Components

Why is a suction-line accumulator used on some heat pump systems?

  1. To reduce the pressure drop across the indoor coil
  2. To store excess refrigerant when the system is in the heating mode only
  3. To prevent liquid refrigerant from reaching the compressor during off-cycle migration or low-load operation Correct answer.
  4. To increase the subcooling at the condenser outlet

Explanation

An accumulator traps liquid refrigerant and lets it boil off before vapor enters the compressor, protecting it from slugging. This is especially valuable on heat pumps where refrigerant migration and floodback risk are higher.

Question 7Heat Pump Fundamentals and System Components

A heat pump thermostat is set to HEAT and the indoor fan runs, but the outdoor unit never starts. Which component is designed to prevent compressor operation when the outdoor coil is too cold to absorb heat efficiently?

  1. The high-pressure switch
  2. The condensate float switch
  3. The outdoor thermostat or low-ambient lockout control Correct answer.
  4. The indoor blower limit switch

Explanation

A low-ambient or outdoor thermostat locks out the compressor at low outdoor temperatures so the system relies on supplemental heat rather than operating outside its useful range. It is the control specifically intended to stop the compressor in that condition.

Question 8Heat Pump Fundamentals and System Components

Which refrigerant line connects the outdoor unit to the indoor coil and carries vapor in the cooling mode but liquid in the heating mode?

  1. The suction line
  2. The discharge line
  3. The liquid line Correct answer.
  4. The common line

Explanation

The liquid line carries condensed liquid from the condenser to the metering device; in a heat pump the condenser location changes with mode, so this line's role flips between modes. The suction and discharge lines always carry vapor at low and high pressure respectively.

Question 9Heat Pump Fundamentals and System Components

During a heating-mode check, the technician measures a refrigerant temperature at the indoor coil that is lower than the return-air temperature. What does this indicate?

  1. The reversing valve is stuck in the heating position
  2. The system is operating normally because the indoor coil is the evaporator
  3. The metering device is overfeeding refrigerant
  4. The indoor coil is not functioning as the condenser as it should in heating mode Correct answer.

Explanation

In heating mode the indoor coil must be hotter than the return air so it can reject heat into the space. A coil colder than return air shows the coil is acting as an evaporator, pointing to a reversing-valve or mode-control fault.

Question 10Heat Pump Fundamentals and System Components

A technician is checking charge on a heat pump in heating mode using the subcooling method. Where should the subcooling be measured?

  1. At the compressor discharge port
  2. At the outlet of the outdoor coil, which is the condenser in heating mode
  3. At the outlet of the indoor coil, which is the condenser in heating mode Correct answer.
  4. At the accumulator inlet

Explanation

Subcooling is measured at the condenser outlet, and in heating mode the condenser is the indoor coil. Measuring there compares liquid-line temperature to the saturated condensing temperature derived from the high-side pressure.

Question 11Heat Pump Fundamentals and System Components

Which condition most directly causes a heat pump to enter defrost during heating operation?

  1. The indoor thermostat calls for a temperature above setpoint
  2. The indoor blower motor draws excessive current
  3. The outdoor coil temperature sensor or pressure switch signals that frost has built up on the coil Correct answer.
  4. The compressor suction pressure rises above the cut-out setting

Explanation

Defrost is initiated when the control senses that the outdoor coil is cold enough and frost has accumulated, typically through a coil temperature sensor or a pressure switch across the coil. The board then reverses the cycle or energizes defrost heaters to melt the frost.

Question 12Heat Pump Fundamentals and System Components

What is the purpose of the outdoor fan cycling off during a defrost cycle on many heat pumps?

  1. To prevent the reversing valve from shifting
  2. To keep the outdoor coil warm enough to melt frost quickly and prevent refreezing Correct answer.
  3. To lower the discharge pressure below the high-pressure cut-out
  4. To reduce compressor amp draw during defrost

Explanation

Stopping the outdoor fan reduces heat removal from the outdoor coil so the hot discharge gas can raise coil temperature and melt frost efficiently. This shortens defrost time and helps prevent refreezing after the cycle.

Question 13Heat Pump Fundamentals and System Components

A heat pump uses electric resistance strip heat as auxiliary heat. When does the auxiliary heat normally energize?

  1. Whenever the compressor is running in heating mode
  2. When the heat pump cannot meet the load alone, such as below the balance point or during defrost Correct answer.
  3. Whenever the outdoor fan is operating
  4. Only when the system is in cooling mode

Explanation

Auxiliary strip heat is staged on when heat pump capacity is insufficient for the load, which occurs below the balance point or during defrost when the system temporarily cools the space. It supplements rather than replaces normal heat pump operation.

Question 14Heat Pump Fundamentals and System Components

Which component prevents refrigerant from migrating to the compressor during the off cycle in a system without an accumulator?

  1. The high-pressure switch
  2. The indoor blower relay
  3. The crankcase heater Correct answer.
  4. The defrost thermostat

Explanation

A crankcase heater warms the compressor sump so refrigerant that migrates during the off cycle is boiled out of the oil. This prevents liquid slugging and oil dilution on startup.

Question 15Heat Pump Fundamentals and System Components

A technician finds that the indoor coil in heating mode is hot and the outdoor coil is cold, but the system is not absorbing heat well and pressures are low. Which additional check is most appropriate?

  1. Verify that the indoor blower is set to the highest speed
  2. Verify that the outdoor coil is clean and the outdoor fan is moving adequate air Correct answer.
  3. Verify that the reversing valve solenoid is de-energized
  4. Verify that the thermostat is in cooling mode

Explanation

In heating mode the outdoor coil is the evaporator, so poor heat absorption with low pressures points to restricted airflow across that coil. A dirty coil or weak outdoor fan limits the heat source and depresses suction pressure.

Question 16Heat Pump Fundamentals and System Components

What is the function of the check valve associated with the metering device on a heat pump?

  1. To prevent refrigerant from flowing through the liquid line in either mode
  2. To allow refrigerant to bypass the inactive metering device in the opposite mode Correct answer.
  3. To isolate the accumulator during defrost
  4. To regulate compressor discharge pressure

Explanation

Heat pumps often use two metering devices, one for each mode, and a check valve lets refrigerant bypass the device that is not active. This ensures the correct restriction is applied only in the direction of flow for that mode.

Question 17Heat Pump Fundamentals and System Components

Which statement correctly describes the relationship between outdoor ambient temperature and heat pump heating capacity?

  1. Heating capacity is independent of outdoor ambient temperature
  2. Heating capacity decreases as outdoor ambient temperature falls Correct answer.
  3. Heating capacity increases as outdoor ambient temperature falls
  4. Heating capacity decreases as outdoor ambient temperature rises

Explanation

As outdoor air gets colder, the temperature difference between the refrigerant and the air shrinks, so the evaporator absorbs less heat and capacity drops. This declining capacity curve is why a balance point and supplemental heat are needed.

Question 18Heat Pump Fundamentals and System Components

A technician is verifying that a heat pump is correctly wired for the defrost cycle. Which terminal on the defrost board typically energizes the reversing valve during defrost?

  1. The terminal that controls the outdoor fan motor
  2. The terminal that powers the indoor blower on high speed
  3. The terminal that powers the reversing valve solenoid for cooling-mode operation Correct answer.
  4. The terminal that supplies the crankcase heater

Explanation

Defrost is accomplished by shifting the reversing valve to the cooling position so hot discharge gas flows through the outdoor coil. The defrost board energizes the same solenoid circuit used for cooling to make that shift.

Question 19Heat Pump Fundamentals and System Components

Which of the following best explains why heat pumps are rated with both a heating capacity and a coefficient of performance at specific outdoor conditions?

  1. Efficiency is constant but capacity varies with line voltage
  2. Ratings are only required for cooling mode, so heating ratings are informational
  3. Capacity and efficiency vary significantly with outdoor temperature, so ratings must reference defined conditions Correct answer.
  4. Capacity is constant but efficiency varies with indoor humidity

Explanation

Because the outdoor air is the heat source in heating mode, both delivered capacity and efficiency change markedly with ambient temperature. Standard ratings therefore specify the outdoor and indoor conditions so equipment can be compared fairly.

Question 20Heat Pump Fundamentals and System Components

A heat pump in heating mode has a suction pressure that is lower than expected and a high superheat at the compressor. Which condition is most consistent with these readings?

  1. A stuck-open reversing valve bleeding discharge into suction
  2. A failed outdoor fan motor causing high airflow
  3. An overcharge of refrigerant
  4. A restricted or underfed metering device in the heating-mode circuit Correct answer.

Explanation

Low suction pressure with high superheat indicates the evaporator is being starved of refrigerant, which occurs when the active metering device is restricted or underfeeding. Overcharge and discharge-to-suction leakage would raise suction pressure instead.

Question 21Heat Pump Fundamentals and System Components

During a defrost cycle, the technician observes that the outdoor fan continues to run and the coil never fully clears. Which is the most likely cause?

  1. The high-pressure switch is open
  2. The indoor blower is running on low speed
  3. The crankcase heater is energized
  4. The defrost board is not cycling the outdoor fan off during defrost Correct answer.

Explanation

Continued outdoor fan operation during defrost removes the heat needed to melt frost, so the coil clears slowly or not at all. The defrost board should de-energize the outdoor fan for the duration of the cycle.

Question 22Heat Pump Fundamentals and System Components

A heat pump with a thermostatic expansion valve shows normal pressures in cooling mode but low suction pressure and poor heating performance. Which component is the most likely cause?

  1. The heating-mode expansion valve or its check valve Correct answer.
  2. The indoor blower capacitor
  3. The compressor run capacitor
  4. The outdoor fan blade pitch

Explanation

Because cooling mode is normal, the compressor, condenser, and cooling metering path are functioning. A fault limited to heating mode points to the heating-mode metering device or its check valve restricting flow.

Question 23Heat Pump Fundamentals and System Components

A technician calculates that a heat pump's heating capacity at the design outdoor temperature is 24,000 Btu/h while the building heat loss is 32,000 Btu/h. What does this indicate about the system design?

  1. The heat pump is oversized and should be replaced with a smaller unit
  2. Supplemental heat totaling about 8,000 Btu/h is needed at design conditions Correct answer.
  3. The system will maintain setpoint without auxiliary heat because capacity exceeds loss
  4. The balance point is above the design temperature and no supplemental heat is needed

Explanation

The capacity shortfall at design conditions is the difference between heat loss and heat pump capacity, here about 8,000 Btu/h. That shortfall must be covered by auxiliary heat sized to the design load.

Question 24Heat Pump Fundamentals and System Components

Which condition would cause a heat pump to remain in defrost longer than normal and then terminate on time rather than temperature?

  1. A thermostat setpoint set too high
  2. A low refrigerant charge
  3. A failed outdoor coil temperature sensor causing the board to rely on its time limit Correct answer.
  4. A dirty indoor air filter

Explanation

When the coil temperature sensor fails to report that the coil is warm enough, the defrost board falls back to its maximum time limit to terminate the cycle. The result is an extended defrost that ends on time rather than on coil temperature.

Question 25Heat Pump Fundamentals and System Components

A heat pump is installed with the outdoor unit below the indoor coil and a long vertical suction line in heating mode. Which design consideration is most important for reliable compressor lubrication?

  1. Providing adequate refrigerant velocity and oil return in the suction riser Correct answer.
  2. Increasing the refrigerant charge to fill the vertical line
  3. Reducing the indoor blower speed to lower suction pressure
  4. Installing a second accumulator at the indoor coil

Explanation

Oil travels with refrigerant velocity, so a vertical suction riser must be sized and configured to keep velocity high enough for oil return to the compressor. Insufficient velocity allows oil to pool in the line and starve the compressor.

Question 26Heat Pump Fundamentals and System Components

In a heat pump operating in the cooling mode, which component is responsible for rejecting heat to the outdoor air?

  1. The reversing valve
  2. The indoor coil
  3. The outdoor coil Correct answer.
  4. The accumulator

Explanation

In cooling mode, the outdoor coil functions as the condenser, rejecting heat absorbed from the indoor space to the outside air. The indoor coil acts as the evaporator, absorbing heat from the conditioned space.

Question 27Heat Pump Fundamentals and System Components

What is the primary function of the reversing valve in a heat pump?

  1. To control the indoor blower speed for comfort
  2. To modulate the outdoor fan speed based on ambient temperature
  3. To bypass the metering device during defrost
  4. To reverse the direction of refrigerant flow between heating and cooling modes Correct answer.

Explanation

The reversing valve redirects refrigerant flow so that the indoor and outdoor coils swap roles as evaporator and condenser, enabling the heat pump to provide both heating and cooling. It is controlled by the thermostat mode selection.

Question 28Heat Pump Fundamentals and System Components

Which type of metering device is commonly used in heat pumps because it can control refrigerant flow in both heating and cooling modes?

  1. A thermostatic expansion valve (TXV) Correct answer.
  2. A capillary tube
  3. A fixed-bore orifice
  4. A piston with a check valve

Explanation

A thermostatic expansion valve (TXV) modulates refrigerant flow in response to evaporator load and can be designed to operate in both flow directions, making it suitable for heat pumps. Fixed-bore or piston devices require check valves to bypass in one mode.

Question 29Heat Pump Fundamentals and System Components

A technician is servicing a heat pump and notices that the suction line is frosted in the heating mode. Which condition is the most likely cause?

  1. A restricted liquid line filter drier
  2. Low refrigerant charge Correct answer.
  3. A failed outdoor fan motor
  4. An overcharged system

Explanation

Frost on the suction line in heating mode indicates that the refrigerant is below freezing and absorbing heat improperly, often due to low charge or a restriction. Low charge reduces pressure and temperature, leading to frost formation.

Question 30Heat Pump Fundamentals and System Components

Which component in a heat pump system is responsible for adding heat to the indoor space when the outdoor temperature is below the balance point?

  1. The compressor
  2. The outdoor fan
  3. The reversing valve
  4. The auxiliary electric resistance heaters Correct answer.

Explanation

When outdoor temperature falls below the balance point, the heat pump's capacity is insufficient to meet the building load, so auxiliary electric resistance heaters energize to supplement heating. The compressor alone cannot provide enough heat in these conditions.

Question 31Heat Pump Fundamentals and System Components

During a heating cycle, the outdoor coil temperature is measured at 25°F while the outdoor ambient is 35°F. What does this indicate about the coil's ability to absorb heat?

  1. The coil is absorbing heat effectively because it is colder than ambient. Correct answer.
  2. The coil has a refrigerant leak.
  3. The coil is in defrost mode.
  4. The coil is not absorbing heat because it is warmer than ambient.

Explanation

For the outdoor coil to absorb heat from the outdoor air, its temperature must be lower than the ambient air temperature. A coil temperature of 25°F with 35°F ambient provides a 10°F temperature difference, allowing heat transfer to occur.

Question 32Heat Pump Fundamentals and System Components

What is the purpose of the defrost control board in a heat pump?

  1. To regulate the indoor blower speed for different modes
  2. To control the reversing valve during cooling mode
  3. To monitor outdoor coil temperature and initiate defrost cycles as needed Correct answer.
  4. To provide a backup heat source if the compressor fails

Explanation

The defrost control board uses sensors to monitor outdoor coil temperature and other inputs to determine when frost accumulation is likely, then initiates a defrost cycle to clear the coil. It also terminates defrost when the coil is clear.

Question 33Heat Pump Fundamentals and System Components

A heat pump is installed with a long vertical suction line in heating mode. Which potential issue should the technician be aware of?

  1. The liquid line may flash prematurely.
  2. The defrost cycle may be shortened.
  3. The suction line may vibrate excessively.
  4. Oil return to the compressor may be inadequate. Correct answer.

Explanation

In heating mode, the suction line is the outdoor-to-indoor line, and a long vertical rise can hinder oil return to the compressor because oil tends to accumulate in low spots or travel slowly against gravity. Proper line sizing and oil traps are important to ensure oil returns.

Question 34Heat Pump Fundamentals and System Components

Which of the following best describes the function of the accumulator in a heat pump system?

  1. To separate oil from the refrigerant
  2. To increase the refrigerant charge in heating mode
  3. To prevent liquid refrigerant from entering the compressor Correct answer.
  4. To store excess refrigerant during low load conditions

Explanation

The accumulator is located on the suction line and traps any liquid refrigerant that may have escaped the evaporator, allowing it to vaporize before reaching the compressor. This prevents compressor slugging and damage.

Question 35Heat Pump Fundamentals and System Components

A technician is checking the operation of a heat pump in heating mode and finds that the indoor coil is cooler than the indoor air temperature. What does this indicate?

  1. The outdoor fan is not running.
  2. The system is operating normally in heating mode.
  3. The auxiliary heat is energized.
  4. The reversing valve may be stuck in the cooling position. Correct answer.

Explanation

In heating mode, the indoor coil should be hot (condenser) and the outdoor coil cold (evaporator). If the indoor coil is cooler than the indoor air, it is acting as an evaporator, indicating the reversing valve is likely stuck in cooling mode or not energized.

Question 36Heat Pump Fundamentals and System Components

What is the primary reason for using a crankcase heater on a heat pump compressor?

  1. To increase the compressor's heating capacity
  2. To warm the compressor oil and prevent refrigerant migration during the off cycle Correct answer.
  3. To provide additional heat to the indoor coil
  4. To reduce the compressor's operating temperature

Explanation

A crankcase heater warms the compressor oil when the compressor is off, which helps keep refrigerant from condensing and diluting the oil. This prevents lubrication problems and potential compressor damage on startup.

Question 37Heat Pump Fundamentals and System Components

During a heating mode check, a technician measures a 20°F temperature difference between the return air and supply air. Which conclusion is most appropriate?

  1. The system is operating within a typical temperature rise range. Correct answer.
  2. The system is overcharged.
  3. The reversing valve is stuck.
  4. The indoor blower is set too high.

Explanation

A temperature rise of 20°F across the indoor coil in heating mode is generally within the typical range for a heat pump without auxiliary heat. This indicates the system is absorbing and delivering heat properly.

Question 38Heat Pump Fundamentals and System Components

Which of the following components is unique to a heat pump system compared to a standard air conditioner?

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

Explanation

The reversing valve is a component specific to heat pumps, allowing the system to switch between heating and cooling by reversing refrigerant flow. Standard air conditioners only cool and do not have this valve.

Question 39Heat Pump Fundamentals and System Components

A heat pump is operating in heating mode and the outdoor coil begins to frost. Which condition will the defrost control use to initiate defrost?

  1. Only the indoor thermostat demand
  2. Only the suction pressure
  3. A combination of coil temperature and time Correct answer.
  4. Only the outdoor ambient temperature

Explanation

Defrost is typically initiated when the outdoor coil temperature falls below a set point and a predetermined time has elapsed, ensuring frost has accumulated. Some controls also use demand defrost based on temperature differential.

Question 40Heat Pump Fundamentals and System Components

What is the function of the check valve in a heat pump's outdoor unit?

  1. To control the direction of the reversing valve
  2. To prevent refrigerant from flowing through the outdoor coil
  3. To allow refrigerant to bypass the outdoor metering device in one mode Correct answer.
  4. To regulate the outdoor fan speed

Explanation

A check valve is often used in conjunction with a fixed orifice or piston to allow refrigerant to bypass the outdoor metering device when it is not needed, such as in heating mode. This ensures proper flow direction and metering.

Question 41Heat Pump Installation and Commissioning

Before brazing the refrigerant lines on a new split-system heat pump, the technician must flow dry nitrogen through the tubing. What is the primary purpose of this practice?

  1. To prevent oxidation and scale from forming inside the tubing Correct answer.
  2. To cool the joint so the filler alloy sets faster
  3. To purge moisture out of the compressor crankcase
  4. To pressurize the line so leaks can be detected during brazing

Explanation

Heating copper in the presence of air forms copper oxide scale on the inside of the tubing, and that scale later migrates to metering devices, reversing valves, and compressor bearings. A slow dry-nitrogen purge displaces oxygen so the interior stays clean. It does not cool the joint, dry the crankcase, or serve as a leak test.

Question 42Heat Pump Installation and Commissioning

A heat pump is being installed in a coastal location where the outdoor unit will sit on a pad. Which practice best protects the installation from corrosion and airflow problems?

  1. Seal the cabinet seams with silicone to keep salt air out
  2. Set the unit directly on the soil and backfill around the base
  3. Raise the unit on a pad above expected snow and water levels with clearances per the manufacturer Correct answer.
  4. Enclose the coil side with a solid fence tight against the cabinet

Explanation

Manufacturer clearances and elevation above snow or flood levels keep the coil clear for airflow and protect the base from standing water and corrosion. A solid barrier tight to the coil blocks discharge air and recirculation, and sealing cabinet seams traps moisture rather than excluding it. Setting the unit on bare soil accelerates rust and settling.

Question 43Heat Pump Installation and Commissioning

During commissioning of an air-source heat pump, the installer must verify that the condensate from the outdoor unit in heating mode has a path away from the unit. Why is this important?

  1. Drain water is required to lubricate the reversing valve
  2. The defrost board uses condensate as a sensor reference
  3. Defrost water can refreeze and damage the coil or fan Correct answer.
  4. Condensate improves the efficiency of the outdoor coil

Explanation

In heating mode the outdoor coil runs below freezing and collects frost, and defrost cycles melt it into water. If that water cannot drain away, it refreezes around the coil, fan, and base pan, which can damage components and block airflow. Condensate is a byproduct, not an efficiency aid, sensor reference, or lubricant.

Question 44Heat Pump Installation and Commissioning

Which action is required before opening the service valves on a factory-charged split heat pump after the line set and indoor coil have been connected?

  1. Energize the compressor to pull a vacuum through the gauge manifold
  2. Charge the line set with liquid refrigerant before evacuation
  3. Open both service valves fully and then leak test the system
  4. Evacuate the line set and indoor coil to the manufacturer's specified micron level Correct answer.

Explanation

The line set and indoor coil contain air and moisture that must be removed by deep evacuation before the factory charge is released. Evacuating to the specified micron level and holding a decay test confirms the circuit is dry and tight. Compressor-assisted evacuation, pre-charging, or opening valves before evacuation would contaminate the system.

Question 45Heat Pump Installation and Commissioning

A technician is setting up the low-voltage control wiring on a new heat pump with a variable-speed air handler. Which terminal must be connected so the indoor blower delivers the airflow the heat pump expects in heating mode?

  1. The R terminal only, since it powers the thermostat
  2. The dedicated blower-speed or communicating control terminal specified by the manufacturer Correct answer.
  3. The C terminal, which carries the blower speed signal
  4. The Y terminal, which controls indoor airflow directly

Explanation

Variable-speed and communicating air handlers select blower airflow from dedicated speed taps or a data link defined by the manufacturer, and heating airflow often differs from cooling airflow. The R terminal is 24 V power, C is common, and Y is the compressor contactor signal, none of which sets blower speed.

Question 46Heat Pump Installation and Commissioning

When performing a startup leak check on a newly installed heat pump, which method is appropriate for the refrigerant circuit before evacuation?

  1. Bubble solution on joints while the system is at 0 psig
  2. Dry nitrogen pressure test with a trace of refrigerant and an electronic leak detector Correct answer.
  3. Vacuum decay test only, with no pressure test
  4. Oxygen pressure test at the manufacturer's test pressure

Explanation

A pressure test with dry nitrogen, often with a small trace of refrigerant for the electronic detector, reveals leaks at joints before evacuation. Oxygen is never used because it is dangerous with refrigerant oil, bubble solution at 0 psig shows nothing, and a vacuum decay test alone is not a substitute for a positive-pressure leak check.

Question 47Heat Pump Installation and Commissioning

Which instrument is used to verify that the line voltage supplied to a new heat pump condensing unit matches the nameplate rating during commissioning?

  1. Manifold gauge set on the suction service port
  2. Megohmmeter connected across the compressor terminals
  3. Digital multimeter set to measure AC voltage at the disconnect Correct answer.
  4. Clamp meter set to measure current on the compressor common

Explanation

Line voltage is verified with a voltmeter at the disconnect or contactor line side and compared with the nameplate rating and allowable tolerance. A clamp meter reads current, gauges read pressures, and a megohmmeter checks insulation resistance, none of which confirm supply voltage.

Question 48Heat Pump Installation and Commissioning

A new heat pump installation requires the thermostat to control auxiliary heat. Which configuration ensures auxiliary heat is available only when it is actually needed?

  1. Energize auxiliary heat whenever the compressor runs
  2. Lock out auxiliary heat above a set outdoor temperature using the balance point setting Correct answer.
  3. Disable the outdoor temperature sensor so auxiliary heat always stages with second stage
  4. Wire auxiliary heat to the emergency heat terminal only

Explanation

A balance-point setting locks out auxiliary resistance heat above a chosen outdoor temperature so the compressor handles the load efficiently. Energizing auxiliary heat with every compressor call wastes energy, and removing the outdoor sensor defeats the lockout. Emergency heat is a manual mode, not a normal staging strategy.

Question 49Heat Pump Installation and Commissioning

A technician is commissioning a split heat pump and needs to verify the refrigerant charge in heating mode. Which approach is appropriate?

  1. Add refrigerant until the suction pressure equals the cooling-mode target
  2. Use the manufacturer's heating-mode charging chart or weigh-in method Correct answer.
  3. Charge to a fixed superheat of 20°F in all modes
  4. Judge charge by the temperature of the liquid line alone

Explanation

In heating mode the indoor coil becomes the condenser and the outdoor coil the evaporator, so cooling-mode subcooling targets no longer apply. Manufacturers provide heating-mode charts based on outdoor temperature and pressures, or specify a weigh-in charge for the line set and coil volume. Fixed superheat values and liquid-line feel are not valid charging methods.

Question 50Heat Pump Installation and Commissioning

During a cooling-mode startup, the technician measures a 12°F temperature difference across the indoor coil when the manufacturer expects 18°F to 22°F. Which condition is the most likely cause?

  1. Low indoor airflow or an undercharged system Correct answer.
  2. Outdoor ambient temperature below 60°F
  3. Excessive refrigerant charge
  4. A correctly operating system with high sensible capacity

Explanation

A small temperature split across the indoor coil in cooling suggests insufficient heat exchange, commonly from low airflow (dirty filter, restrictive duct, low blower speed) or low charge. Overcharge typically raises the split and pressures. A split far below the range is not a sign of correct operation, and low ambient alone does not explain the indoor split.