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Question 1Core (safety, tools, basic refrigeration and electrical fundamentals)

When connecting gauges to a residential split system to handle liquid refrigerant, which personal protective equipment is required?

  1. Insulating gloves and splash goggles Correct answer.
  2. Safety glasses only
  3. Cotton work gloves
  4. Ear plugs and a dust mask

Explanation

Liquid refrigerant at atmospheric pressure boils far below freezing, so a splash or a wetted glove causes instant frostbite. Insulating gloves and splash goggles protect the hands and eyes from liquid spray and from a burst of cold vapor.

Question 2Core (safety, tools, basic refrigeration and electrical fundamentals)

On a standard three-hose manifold gauge set, which color identifies the low-side gauge and hose?

  1. Green
  2. Red
  3. Blue Correct answer.
  4. Yellow

Explanation

Manifold sets follow a standard color code so a technician can connect quickly without crossing the high and low sides. Blue is the low-side (suction) gauge and hose, red is the high-side (discharge) gauge and hose, and yellow is the center hose used for charging or evacuation.

Question 3Core (safety, tools, basic refrigeration and electrical fundamentals)

Electrical resistance is measured in which unit?

  1. Watts
  2. Volts
  3. Ohms Correct answer.
  4. Amperes

Explanation

Resistance opposes current flow and is expressed in ohms, symbolized by the Greek letter omega. Volts describe electrical potential difference, amperes describe current flow, and watts describe power.

Question 4Core (safety, tools, basic refrigeration and electrical fundamentals)

In a vapor-compression refrigeration system, which component absorbs heat from the air being cooled?

  1. Evaporator Correct answer.
  2. Metering device
  3. Compressor
  4. Condenser

Explanation

The evaporator is the indoor coil where low-pressure refrigerant boils and absorbs heat from the airstream passing over it. The condenser rejects that heat outdoors, the compressor raises the vapor pressure and temperature, and the metering device controls refrigerant flow into the evaporator.

Question 5Core (safety, tools, basic refrigeration and electrical fundamentals)

Before opening the electrical compartment of an energized rooftop unit, a technician should first:

  1. Remove the blower panel and the filter
  2. Discharge the run capacitor and start the unit
  3. Lock out the disconnect and verify with a meter Correct answer.
  4. Turn the thermostat to fan-on and wait

Explanation

Lockout/tagout isolates the equipment from its power source and prevents another person from energizing it while work is in progress. The circuit must then be verified de-energized with a meter, because a disconnect or breaker label alone does not prove the line is dead.

Question 6Core (safety, tools, basic refrigeration and electrical fundamentals)

Which instrument is used to measure the vacuum level in a system during evacuation?

  1. Electronic micron gauge Correct answer.
  2. Manifold gauge set
  3. Sling psychrometer
  4. Anemometer

Explanation

A micron gauge reads deep vacuum directly at the system, in microns of mercury, and can resolve levels far below what a manifold gauge can show. Its resolution is what allows a technician to confirm that evacuation has removed moisture-laden air.

Question 7Core (safety, tools, basic refrigeration and electrical fundamentals)

A 24-volt control circuit has a total resistance of 8 ohms. What current flows through the circuit?

  1. 12 A
  2. 0.33 A
  3. 3 A Correct answer.
  4. 192 A

Explanation

Ohm's law states that current equals voltage divided by resistance. Dividing 24 volts by 8 ohms gives 3 amperes.

Question 8Core (safety, tools, basic refrigeration and electrical fundamentals)

R-410A is a zeotropic blend. To keep the composition correct, refrigerant should be removed from the cylinder:

  1. as a vapor
  2. as a vapor after warming the cylinder
  3. as a liquid Correct answer.
  4. in either state, because the composition does not change

Explanation

In a zeotropic blend the components have different boiling points, so drawing vapor off the top removes the more volatile component first and leaves the remaining charge with a different composition. Charging as a liquid keeps the blended ratio intact.

Question 9Core (safety, tools, basic refrigeration and electrical fundamentals)

What is the maximum liquid fill level for a refrigerant recovery cylinder?

  1. 95 percent
  2. 50 percent
  3. 80 percent Correct answer.
  4. 100 percent

Explanation

Recovery cylinders must be filled to no more than 80 percent of their capacity by liquid volume so that liquid expansion with rising temperature leaves vapor space. Filling beyond that can result in a hydrostatic condition and relief valve discharge.

Question 10Core (safety, tools, basic refrigeration and electrical fundamentals)

What is the correct way to prepare a run capacitor before removing it from a circuit?

  1. Discharge it through a bleeder resistor, then verify Correct answer.
  2. Replace it whenever the cabinet is opened
  3. Test it with an ohmmeter while the unit is energized
  4. Assume it is empty once the disconnect is open

Explanation

A capacitor can store a dangerous charge after the power is removed, so its terminals must be bled down through a resistor rated for the job. Verifying with a meter confirms the stored voltage is gone before the terminals are touched.

Question 11Core (safety, tools, basic refrigeration and electrical fundamentals)

Which gas is used for pressure testing a refrigeration system?

  1. Acetylene
  2. Dry nitrogen Correct answer.
  3. Compressed air
  4. Oxygen

Explanation

Dry nitrogen is inert and does not introduce moisture, oxygen, or fuel into the system, and it is supplied through a pressure regulator to a safe test pressure. Oxygen and compressed air can combine with refrigerant oil under pressure and create a fire or explosion hazard.

Question 12Core (safety, tools, basic refrigeration and electrical fundamentals)

Subcooling is defined as:

  1. suction line temperature minus evaporating saturation temperature
  2. temperature rise measured across the condenser coil
  3. liquid line temperature minus condensing saturation temperature Correct answer.
  4. pressure drop measured across the metering device

Explanation

Subcooling measures how far the liquid leaving the condenser has been cooled below its condensing saturation temperature. It is a check of how much liquid is stacked in the condenser and is used to verify charge on a fixed-orifice system.

Question 13Core (safety, tools, basic refrigeration and electrical fundamentals)

In a 24-volt control circuit, which component closes the line-voltage contacts that power the compressor?

  1. Contactor Correct answer.
  2. Thermostat
  3. Transformer
  4. Capacitor

Explanation

The contactor coil is energized by the low-voltage control circuit, and its magnetic pull closes the heavy line-voltage contacts feeding the compressor. The thermostat only switches the low-voltage signal that energizes the coil.

Question 14Core (safety, tools, basic refrigeration and electrical fundamentals)

Evaporator outlet superheat measures 2°F on a system with a piston metering device. This indicates:

  1. An overcharged system with excess liquid in the condenser
  2. Liquid refrigerant flooding the evaporator coil Correct answer.
  3. Normal operation at design conditions
  4. A restricted liquid line or clogged filter-drier

Explanation

Superheat is the margin above saturation at the evaporator outlet, so a very low value means the refrigerant has not fully boiled off before leaving the coil. That condition can return liquid to the compressor and cause slugging and oil dilution.

Question 15Core (safety, tools, basic refrigeration and electrical fundamentals)

Under ASHRAE Standard 34, which of these refrigerants carries the A1 safety classification?

  1. R-717 (ammonia)
  2. R-410A Correct answer.
  3. R-290 (propane)
  4. R-32

Explanation

The A1 classification means low toxicity in Group A and no flame propagation in Group 1 according to ASHRAE 34 testing. R-410A is rated A1, while propane, ammonia, and R-32 fall into more hazardous classes.

Question 16Core (safety, tools, basic refrigeration and electrical fundamentals)

A voltmeter placed across a switch in an energized circuit reads 0 volts. This means:

  1. The switch has developed high contact resistance
  2. The switch contacts are open and the circuit is broken
  3. The switch is closed with negligible voltage drop Correct answer.
  4. The circuit is de-energized at the panel

Explanation

Voltage is a difference in potential, so a good closed switch has nearly the same potential on both terminals and shows almost no drop. A reading of full circuit voltage across the switch is what indicates open contacts.

Question 17Core (safety, tools, basic refrigeration and electrical fundamentals)

A cylinder of R-134a reads 71 psig at 70°F. A second cylinder of the same refrigerant at 70°F that contains only half as much liquid will read:

  1. a higher pressure because of the larger vapor space
  2. about 35 psig
  3. the same 71 psig Correct answer.
  4. zero until the cylinder is inverted

Explanation

As long as liquid and vapor are both present, a refrigerant's pressure is its saturation pressure at that temperature and depends only on temperature. The amount of liquid in the cylinder does not change the pressure until the liquid is completely gone.

Question 18Core (safety, tools, basic refrigeration and electrical fundamentals)

A single-phase compressor shows 1.2 ohms from common to run, 2.0 ohms from common to start, and 3.2 ohms from run to start. These readings indicate:

  1. Normal windings Correct answer.
  2. A shorted run winding
  3. An open start winding
  4. A winding grounded to the shell

Explanation

The run and start windings are joined at the common terminal, so the resistance measured run-to-start should equal the sum of the two individual windings. Here 1.2 plus 2.0 equals 3.2 ohms, which matches the measured value and confirms the windings are intact.

Question 19Core (safety, tools, basic refrigeration and electrical fundamentals)

A system has low suction pressure, high evaporator superheat, and a clear sight glass. Which condition best explains these readings?

  1. A restricted liquid line filter-drier Correct answer.
  2. A metering device that is overfeeding
  3. A dirty condenser coil
  4. An overcharge of refrigerant

Explanation

A restriction in the liquid line limits how much refrigerant reaches the evaporator, so the coil is starved and superheat rises while suction pressure falls. Because the restriction is downstream of the receiver, the sight glass can still show a clear liquid stream.

Question 20Core (safety, tools, basic refrigeration and electrical fundamentals)

Line-to-line voltage readings on a three-phase unit are 240 V, 236 V, and 244 V. How should the technician evaluate this supply?

  1. Unacceptable, because the imbalance exceeds 2%
  2. Acceptable, but only if the current readings are also balanced
  3. Acceptable, because the imbalance is under 2% Correct answer.
  4. Unacceptable, because the imbalance exceeds 5%

Explanation

Voltage imbalance is found by taking the greatest deviation from the average and dividing it by the average. The average here is 240 V with a maximum deviation of 4 V, giving about 1.7 percent, which is within the commonly applied 2 percent limit for motor-powered equipment.

Question 21Air Conditioning

Superheat is best described as:

  1. the temperature drop of the air as it passes across the evaporator coil
  2. the difference between the liquid line temperature and the saturation temperature at discharge pressure
  3. the difference between the actual suction line temperature and the saturation temperature at suction pressure Correct answer.
  4. the temperature difference between the entering and leaving condenser air

Explanation

Superheat is the amount by which the refrigerant vapor is above its saturation temperature at the measured suction pressure. It is found by subtracting the saturation temperature for the suction pressure from the actual suction line temperature. It confirms that no liquid refrigerant is returning to the compressor.

Question 22Air Conditioning

In a properly operating direct-expansion system, the refrigerant entering the evaporator is:

  1. a superheated low-pressure vapor
  2. a low-pressure liquid and vapor mixture Correct answer.
  3. a high-pressure subcooled liquid
  4. a high-pressure superheated vapor

Explanation

The metering device drops pressure and flashes part of the refrigerant before it enters the distributor and coil. This two-phase mixture boils at a low saturation temperature and absorbs heat from the air. By the evaporator outlet, all liquid should be boiled off and a small amount of superheat added.

Question 23Air Conditioning

The primary function of the condenser in a split air conditioning system is to:

  1. reduce the refrigerant pressure before the evaporator
  2. meter the flow of refrigerant into the evaporator
  3. absorb heat from the conditioned space
  4. reject heat from the refrigerant and condense it to a liquid Correct answer.

Explanation

The condenser removes sensible heat from the discharge vapor until it reaches saturation, then removes latent heat to condense it into a liquid. This heat is rejected to the outdoor air moving across the coil. A small additional amount of sensible heat is removed as the liquid is subcooled.

Question 24Air Conditioning

Wet-bulb temperature is best described as:

  1. the saturation temperature of the refrigerant at suction pressure
  2. the temperature of the air measured with a dry-bulb thermometer
  3. the temperature at which water condenses inside the ductwork
  4. the lowest temperature that air can reach by evaporative cooling Correct answer.

Explanation

A wet-bulb thermometer has a moistened wick, and evaporation cools the bulb below the dry-bulb reading. The wet-bulb temperature therefore reflects the moisture content of the air and represents the limit of evaporative cooling. The difference between dry-bulb and wet-bulb is the wet-bulb depression.

Question 25Air Conditioning

The thermostatic expansion valve controls:

  1. refrigerant flow into the evaporator to maintain a set superheat Correct answer.
  2. refrigerant flow into the condenser to maintain head pressure
  3. the compressor discharge pressure during low ambient conditions
  4. the volume of air moving across the evaporator coil

Explanation

The TXV modulates a needle and seat to hold a target superheat at the evaporator outlet. It responds to the bulb pressure at the outlet, the evaporator pressure below the diaphragm, and the spring setting. Because it regulates superheat, charging on these systems is normally done by subcooling.

Question 26Air Conditioning

A heavily fouled evaporator coil most directly causes:

  1. higher than normal subcooling with normal head pressure
  2. reduced airflow and a lower suction pressure Correct answer.
  3. higher head pressure with a normal suction pressure
  4. higher than normal superheat with unchanged airflow

Explanation

A dirty coil blocks airflow and reduces heat transfer, so less heat reaches the refrigerant and the suction pressure drops. Because less of the coil is actively boiling refrigerant, the superheat reading is often unsteady or low. Cleaning the coil and verifying airflow is the correction.

Question 27Air Conditioning

A system shows a suction pressure of 60 psig and a suction line temperature of 62°F. The saturation temperature at 60 psig is approximately 34°F. The measured superheat is:

  1. 96°F of superheat
  2. 28°F of superheat Correct answer.
  3. 2°F of superheat
  4. 28°F of subcooling

Explanation

Superheat equals the suction line temperature minus the saturation temperature for the suction pressure. Subtracting 34°F from 62°F gives 28°F, which is well above the typical target and suggests the coil is being starved of refrigerant. A common cause is undercharge or a restriction in the metering device or liquid line.

Question 28Air Conditioning

On a TXV system, subcooling measured at the condenser outlet is 2°F while the manufacturer specifies 10°F. The most likely cause is:

  1. an undercharge of refrigerant Correct answer.
  2. excessive condenser airflow
  3. an overcharge of refrigerant
  4. a restricted suction line

Explanation

Subcooling indicates how much liquid refrigerant is stacked in the bottom of the condenser, so low subcooling means not enough liquid is being backed up. That points to an undercharge or to the TXV feeding more refrigerant than the system holds. Charge is added only after confirming airflow and that no leaks exist.

Question 29Air Conditioning

Compared with R-22, R-410A systems require:

  1. POE oil and gauges rated for higher pressures Correct answer.
  2. no special attention to oil return in the piping
  3. mineral oil and standard R-22 gauge sets
  4. lower condensing pressures at the same ambient temperature

Explanation

R-410A operates at roughly 50 to 60 percent higher pressures than R-22, so manifold gauge sets and hoses must be rated for it. It is also a blend that uses polyolester (POE) oil, which readily absorbs moisture. Recovery equipment and cylinders must likewise be rated for the higher pressure.

Question 30Air Conditioning

To determine the operating superheat of a system, a technician needs:

  1. condensing temperature and outdoor ambient temperature
  2. suction pressure and entering air wet-bulb temperature
  3. liquid line temperature and discharge pressure
  4. suction line temperature and suction pressure Correct answer.

Explanation

Superheat is the suction line temperature minus the saturation temperature corresponding to the suction pressure. Both readings must be taken at the same point on the suction line, near the evaporator outlet. Comparing that value against the manufacturer's target confirms whether the coil is properly fed.

Question 31Air Conditioning

The difference between the condensing saturation temperature and the outdoor ambient temperature is called the:

  1. condensing split Correct answer.
  2. approach
  3. superheat
  4. evaporator temperature drop

Explanation

The condensing split compares the saturation temperature in the condenser with the air entering the coil. A large split suggests the condenser is rejecting heat poorly, often from dirt, recirculated air, or low airflow. A small split with high head pressure may point to a non-condensable or an overcharge.

Question 32Air Conditioning

Latent heat removal at the evaporator coil:

  1. increases the sensible-to-total ratio of the coil
  2. raises the dry-bulb temperature of the supply air
  3. converts water vapor to liquid without changing air temperature Correct answer.
  4. has no measurable effect on the amount of condensate the coil produces

Explanation

Latent heat is the heat removed when water vapor changes to liquid water on the coil, and it occurs without a change in dry-bulb temperature. The liquid drains away as condensate, which lowers the moisture content of the supply air. Sensible heat removal is the separate process that lowers the air's dry-bulb temperature.

Question 33Air Conditioning

A typical acceptable dry-bulb temperature drop across a properly operating evaporator coil is:

  1. 25°F to 35°F
  2. 16°F to 22°F Correct answer.
  3. 40°F to 50°F
  4. 4°F to 8°F

Explanation

Most residential and light commercial coils are designed for roughly a 16°F to 22°F difference between return and supply air under design conditions. The exact target varies with the wet-bulb entering the coil and must be checked against the manufacturer's data. A drop outside this range usually signals an airflow or charge problem.

Question 34Air Conditioning

An air conditioner satisfies the thermostat quickly on every cycle and then short-cycles, while the refrigerant charge and airflow have been verified as correct. The most likely cause is that the unit:

  1. is oversized for the building load Correct answer.
  2. has a blower set to low speed
  3. has a restricted metering device
  4. has a failed compressor

Explanation

An oversized unit removes sensible heat faster than the space gains it, so the thermostat is satisfied before the coil can remove much moisture. The result is short run times, uneven temperatures, and poor humidity control. Correct sizing to the calculated load is the lasting solution.

Question 35Air Conditioning

Bubbles visible in the liquid line sight glass of a TXV system indicate:

  1. a liquid line restriction or insufficient subcooling Correct answer.
  2. normal operation during high ambient conditions
  3. an excess refrigerant charge
  4. too much airflow across the condenser

Explanation

Flash gas appears when liquid refrigerant pressure drops below its saturation pressure or when not enough liquid is available, such as from a restriction or an undercharge. On a TXV system the correct response is to verify subcooling at the condenser outlet and check for a temperature drop across the filter drier. A solid column of liquid is expected at the sight glass under normal conditions.

Question 36Air Conditioning

A coil removes 36,000 Btu/h of sensible heat with a 20°F temperature drop across it. Using the sensible heat equation, the airflow is approximately:

  1. 3,300 cfm
  2. 800 cfm
  3. 1,200 cfm
  4. 1,670 cfm Correct answer.

Explanation

The sensible heat equation is Btu/h = 1.08 × cfm × temperature difference, so cfm equals Btu/h divided by (1.08 × ΔT). Dividing 36,000 by (1.08 × 20), or 21.6, gives about 1,667 cfm. The 1.08 constant applies to standard air at sea level.

Question 37Air Conditioning

A TXV system shows high superheat with subcooling that matches the manufacturer's target. This most likely means the:

  1. condenser has poor airflow
  2. TXV is overfeeding the evaporator
  3. system is overcharged with refrigerant
  4. TXV is underfeeding the evaporator Correct answer.

Explanation

Normal subcooling shows the condenser has the right amount of liquid, so the problem lies on the low side. High superheat with a properly charged system indicates the valve is not admitting enough refrigerant, as with a lost bulb charge, a sticking valve, or a blocked inlet screen. The starved coil will show a low suction pressure and a small temperature drop.

Question 38Air Conditioning

A coil has a sensible heat ratio of 0.70 and a total capacity of 40,000 Btu/h. The latent capacity is:

  1. 28,000 Btu/h
  2. 12,000 Btu/h Correct answer.
  3. 8,000 Btu/h
  4. 40,000 Btu/h

Explanation

The sensible heat ratio is the sensible capacity divided by the total capacity, so the latent share is one minus that ratio. Here 30 percent of 40,000 Btu/h is the latent portion, or 12,000 Btu/h. The remaining 28,000 Btu/h is sensible capacity.

Question 39Air Conditioning

A fan-cycling or head pressure control on an air-cooled condenser operating in cold weather is used to:

  1. increase superheat at the evaporator outlet
  2. raise the evaporator airflow rate
  3. reduce the running current of the compressor
  4. maintain adequate condensing pressure for proper metering and lubrication Correct answer.

Explanation

Low ambient temperatures drop the condensing pressure, which reduces the pressure difference across the metering device and can starve the evaporator. It also lowers the mass flow of refrigerant returning to the compressor for cooling and oil movement. Cycling the fan or modulating its speed keeps head pressure in a workable range.

Question 40Air Conditioning

A fixed-orifice (piston) system operating at design indoor wet-bulb shows only 3°F of superheat. The most appropriate action is to:

  1. add refrigerant to raise the superheat
  2. recover refrigerant to raise the superheat Correct answer.
  3. install a larger metering piston
  4. increase the condenser airflow

Explanation

With a fixed orifice, superheat rises as charge is removed and falls as charge is added. A superheat well below the target indicates the evaporator is flooded, which risks liquid floodback to the compressor, so refrigerant is recovered. Charge is adjusted in small increments while allowing the system to stabilize.

Question 41Air Distribution

Which supply duct sizing method holds the friction loss per foot of duct constant from the fan to the last outlet?

  1. Equal friction Correct answer.
  2. Constant velocity
  3. Static regain
  4. Velocity reduction

Explanation

The equal friction method sizes every section so that the pressure loss per foot of length is the same throughout the supply system. This simplifies layout work and gives a reasonably self-balancing system with a single friction-rate calculation.

Question 42Air Distribution

A pitot tube reads a velocity pressure of 0.25 in. w.c. in a main supply duct. The air velocity is closest to:

  1. 2500 fpm
  2. 1500 fpm
  3. 1000 fpm
  4. 2000 fpm Correct answer.

Explanation

Velocity in fpm equals 4005 times the square root of velocity pressure in inches of water column. The square root of 0.25 is 0.5, and 4005 times 0.5 is about 2000 fpm.

Question 43Air Distribution

A 12 in. by 12 in. duct carries air at 800 fpm. What is the airflow through the duct?

  1. 533 cfm
  2. 800 cfm Correct answer.
  3. 267 cfm
  4. 400 cfm

Explanation

Airflow equals velocity multiplied by cross-sectional area. A 12 in. by 12 in. duct has an area of 144 square inches, exactly 1 square foot, so 800 fpm times 1 square foot equals 800 cfm.

Question 44Air Distribution

Flexible duct runs should be supported at intervals no greater than:

  1. 4 ft Correct answer.
  2. 10 ft
  3. 8 ft
  4. 6 ft

Explanation

Industry and manufacturer installation standards require flexible duct to be supported at approximately 4 ft intervals, with the duct not allowed to sag between supports. Sagging flattens the duct, reduces its effective diameter, and sharply increases pressure loss and airflow reduction.

Question 45Air Distribution

Which term describes the distance from a supply outlet to the point where the airstream velocity has decayed to a specified terminal value, commonly 50 fpm?

  1. Drop
  2. Entrainment
  3. Spread
  4. Throw Correct answer.

Explanation

Throw is the measured distance from the outlet face to the point where the airstream slows to the stated terminal velocity. It is the primary number used to decide outlet spacing and whether conditioned air reaches the occupied zone.

Question 46Air Distribution

Total pressure at a point inside a duct is equal to:

  1. Velocity pressure alone
  2. Static pressure plus velocity pressure Correct answer.
  3. Static pressure only, measured at the fan outlet
  4. Static pressure minus velocity pressure

Explanation

Total pressure is the algebraic sum of static pressure and velocity pressure at the same point. Static pressure acts against the duct walls, while velocity pressure represents the kinetic energy of the moving airstream.

Question 47Air Distribution

A rectangular duct measures 8 in. by 32 in. What is its aspect ratio?

  1. 8:1
  2. 4:1 Correct answer.
  3. 6:1
  4. 2:1

Explanation

Aspect ratio is the duct width divided by its depth, so 32 divided by 8 equals a 4:1 ratio. Ratios wider than about 4:1 increase friction and make the duct harder to fabricate and support.

Question 48Air Distribution

A blower is rated at 0.50 in. w.c. external static pressure. The filter, coil, and grilles account for 0.15, 0.20, and 0.05 in. w.c. respectively. What static pressure remains available for the duct system?

  1. 0.30 in. w.c.
  2. 0.35 in. w.c.
  3. 0.10 in. w.c. Correct answer.
  4. 0.20 in. w.c.

Explanation

Available static pressure equals the blower's rated external static pressure minus the pressure drops of the components that are not part of the duct run. The three components total 0.40 in. w.c., leaving 0.50 minus 0.40, or 0.10 in. w.c.

Question 49Air Distribution

Where should a volume damper be installed to balance a single branch run off a trunk duct?

  1. In the return air plenum at the air handler
  2. At the branch takeoff near the main trunk Correct answer.
  3. On the fan discharge side of the air handler
  4. At the last outlet on the branch run

Explanation

A damper placed in the branch takeoff controls the entire branch and can be locked in position, which is what balancing requires. Locating it at the last outlet leaves the rest of the run unregulated and the branch cannot be trimmed as a unit.

Question 50Air Distribution

A bedroom with a supply register and a closed door needs a return path. This is normally provided by:

  1. A larger supply diffuser in the room
  2. Opening a window in the adjacent room
  3. A transfer grille or a door undercut Correct answer.
  4. A barometric relief damper in the ceiling

Explanation

A closed door can pressurize the room and choke off supply airflow, so a dedicated return path such as a transfer grille, jumper duct, or door undercut must be sized for the return airflow. This keeps the room at neutral pressure and allows the supply air to enter.