Mixed Deck — All 313D Topics Flashcards

Which insulation vapor barrier placement is correct for a duct located in a hot, humid unconditioned attic?

Answer: Vapor barrier on the outside of the insulation facing the attic

In a hot-humid attic, the vapor barrier must face outward to block moisture from the warm attic air from reaching the cold duct surface.

When installing ductwork for a new residential AC system, what is the purpose of using mastic sealant instead of standard duct tape?

Answer: Mastic provides a durable, long-lasting airtight seal that duct tape cannot maintain over time

Mastic sealant creates a permanent, flexible, airtight bond at duct joints, whereas standard duct tape degrades and loses adhesion over time, allowing air leaks.

A technician is called for a no-cool complaint and finds the suction pressure is unusually low, near 0 psig, and the head pressure is also significantly lower than normal. The suction line at the outdoor unit feels warm to the touch. What is the most likely cause?

Answer: Severe refrigerant leak or empty system

When a system has lost most or all of its refrigerant, there is very little medium to absorb heat in the evaporator or reject it in the condenser. This results in extremely low pressures on both the high and low sides. The lack of refrigerant means no cooling is occurring, leading to a warm suction line.

Which type of refrigerant oil is exclusively used with R-410A systems?

Answer: Polyolester oil (POE)

R-410A systems require polyolester (POE) oil because R-410A is not miscible with mineral or alkylbenzene oils, which would cause oil separation and compressor failure.

What does EPA Section 608 certification test require technicians to know?

Answer: Proper refrigerant handling and leak prevention

EPA Section 608 certification is required for technicians who work with refrigerants in stationary refrigeration and air conditioning equipment. The certification tests knowledge of regulations concerning ozone-depleting substances and substitutes, emphasizing proper recovery, recycling, and reclamation of refrigerants. It also covers leak detection, repair, and safe disposal practices to protect the environment from harmful refrigerant emissions.

When calculating latent heat loads, which source contributes the most latent load in a typical residential kitchen?

Answer: Cooking appliances and occupants

Cooking appliances release significant steam and moisture, and occupants also produce latent heat through perspiration and respiration.

On a standard psychrometric chart, which property is represented on the horizontal (x) axis?

Answer: Dry-bulb temperature

The horizontal axis of a psychrometric chart represents dry-bulb temperature, the fundamental measured air temperature read by a standard thermometer.

What is the primary difference between refrigerant 'recovery,' 'recycling,' and 'reclaiming'?

Answer: Recovery=remove from system; recycling=oil separation/filter on-site; reclaiming=AHRI 700 purity at certified facility

EPA defines recovery as removing refrigerant from a system, recycling as basic on-site cleaning (oil separation, filtering), and reclaiming as reprocessing to AHRI 700 purity at a certified facility.

What does a 'U-factor' (U-value) measure in building envelope load calculations?

Answer: Rate of heat transfer through a building assembly

The U-factor measures how readily heat flows through a building assembly; it is the inverse of R-value (U = 1/R).

What are the primary negative effects of high indoor relative humidity on occupants?

Answer: It promotes mold growth, makes occupants feel warmer, and can cause respiratory irritation

High indoor humidity fosters mold and mildew, makes occupants feel hotter because perspiration evaporates more slowly, and can aggravate asthma and allergies.

The primary purpose of installing a filter-drier in the liquid line of a new residential AC system is to:

Answer: Remove moisture and contaminants that could damage the system

A filter-drier absorbs moisture and traps particulates, protecting the metering device and compressor from contamination and acid formation.

A blueprint's mechanical plan shows a duct line labeled '12x8' and an airflow value of '400 CFM'. What do these two pieces of information represent?

Answer: The duct's dimensions in inches (width x height) and the volume of air it must carry.

On HVAC blueprints, ductwork is dimensioned by its width and height in inches (e.g., 12" wide by 8" high). CFM stands for Cubic Feet per Minute, which is the standard unit for measuring the volume of airflow required for a specific space or duct run.

What causes a compressor to 'short cycle' in a residential air conditioning system?

Answer: Oversized system or faulty thermostat causing rapid on/off cycling

Short cycling typically results from an oversized system that satisfies the thermostat setpoint too quickly or a malfunctioning thermostat, leading to excessive starts and stops.

What happens to airflow velocity when a duct transitions from a smaller to a larger cross-section?

Answer: Velocity decreases and static pressure partially recovers

When a duct expands, the air slows down (by continuity) and some velocity pressure converts back to static pressure—this is called static regain.

Which electrical test would BEST confirm that a compressor motor winding has a ground fault?

Answer: Measure resistance between each winding terminal and the compressor shell/ground

A megohmmeter or ohmmeter reading between a winding terminal and the grounded shell detects insulation breakdown indicating a ground fault.

A technician is preparing to braze a copper suction line to a steel compressor stub. Which of the following is essential for creating a strong, leak-free joint?

Answer: Applying a separate flux to the joint before heating.

When brazing dissimilar metals like copper and steel, a separate flux is required. Phosphorus-bearing alloys (like Phos-Copper) are self-fluxing only on copper-to-copper joints; using them on steel without a flux will result in a brittle, weak joint. The flux cleans the surfaces, prevents oxidation during heating, and promotes the flow of the filler metal.

Which regulation governs the transportation of refrigerant cylinders by road and specifies proper labeling and packaging requirements?

Answer: DOT 49 CFR Part 173

DOT 49 CFR Part 173 establishes packaging, labeling, and hazmat shipping requirements for compressed gas cylinders including refrigerants transported by road.

Which of the following describes the state of the refrigerant as it enters the metering device in a properly functioning air conditioning system?

Answer: High-pressure, warm liquid

After leaving the condenser, the refrigerant has rejected heat to the outdoors and has condensed from a high-pressure vapor into a high-pressure, warm liquid. This subcooled liquid then flows to the metering device.

What is the Apparatus Dew Point (ADP) of a cooling coil?

Answer: The effective average surface temperature of the coil at which moisture condenses

ADP is the effective mean surface temperature of a cooling coil — the theoretical temperature at which the coil would saturate leaving air if bypass factor were zero.

When installing refrigerant piping through a fire-rated wall, what is required by most building codes?

Answer: A fire stop seal must be applied around the penetration

Building codes require fire-stopping materials around any penetration through a fire-rated assembly to maintain the assembly's fire resistance rating.