Mixed Deck — All HVAC Topics Flashcards

A recovery cylinder is color-coded gray with a yellow top. What does this indicate?

Answer: The cylinder contains a mixed or unknown refrigerant

Gray body with yellow top is the standard color code for cylinders containing mixed or unknown refrigerant, as established by ARI (now AHRI) guidelines for recovery cylinders.

Which component in a refrigeration system separates refrigerant vapor from liquid to ensure only vapor enters the compressor in a flooded evaporator system?

Answer: Suction accumulator

A suction accumulator is installed in the suction line to separate and hold any liquid refrigerant, allowing only vapor to pass to the compressor.

What IAQ hazard does a malfunctioning heat exchanger in a forced-air furnace pose?

Answer: Carbon monoxide (CO) poisoning from combustion gases leaking into the supply air stream

A cracked or corroded heat exchanger allows combustion gases—including deadly carbon monoxide—to mix with the circulated air supply, posing serious carbon monoxide poisoning risk.

What role does collaboration play in energy efficiency for HVAC professionals?

Answer: It enhances outcomes through diverse perspectives and shared expertise

Collaboration leverages diverse perspectives and combined expertise to achieve better outcomes than any individual could alone.

In a demand-controlled ventilation (DCV) system, CO2 sensors are used to:

Answer: Modulate outdoor air dampers based on occupancy levels

DCV uses CO2 as a proxy for occupancy; as CO2 rises above setpoint (typically 1100 ppm), the controller opens outdoor air dampers to dilute contaminants and provide fresh air.

What type of mastic sealant is recommended for sealing HVAC duct joints in unconditioned spaces?

Answer: UL 181-listed water-based duct mastic applied with mesh tape

UL 181-listed duct mastic reinforced with fiberglass mesh tape provides a durable, airtight seal that remains flexible across temperature cycles in unconditioned spaces.

What is the primary advantage of a variable-speed compressor in a heat pump?

Answer: It modulates capacity to match load, improving efficiency

Variable-speed compressors adjust their output to match the heating or cooling demand, reducing energy consumption and improving comfort.

Which EPA section governs the handling and recovery of refrigerants?

Answer: Section 608

EPA Section 608 regulates the servicing, maintenance, repair, and disposal of stationary refrigeration and air conditioning equipment to prevent refrigerant venting.

An HVAC technician notices condenser coil fins are bent and restricting airflow. What is the most likely energy impact?

Answer: Increased condensing pressure and reduced system efficiency

Restricted condenser airflow raises head pressure, forcing the compressor to work harder and reducing overall system efficiency.

What is a 'Variable Air Volume' (VAV) system and how does it differ from a 'Constant Volume' (CAV) system?

Answer: VAV varies supply air volume to each zone while maintaining constant supply temperature; CAV delivers constant air volume at varying temperatures

A VAV system delivers conditioned air at constant supply temperature but modulates the volume delivered to each zone using VAV terminal boxes, matching supply to actual demand.

What problems arise from excessively high water velocity in hydronic piping?

Answer: High velocity causes erosion-corrosion, noise, and air entrainment

Excessively high water velocity causes erosion-corrosion at fittings and elbows, generates flow noise, and can cause air bubbles to be entrained.

A geothermal heat pump has a much higher COP than an air-source heat pump in winter. Why?

Answer: Ground temperatures remain relatively stable year-round, providing a more favorable heat source than cold outdoor air

Ground temperatures at depth stay near 50–55°F year-round, giving geothermal heat pumps a much warmer heat source than outdoor air during cold winters, greatly improving COP.

What is the maximum fill level (by weight) allowed when filling a refrigerant recovery cylinder?

Answer: 80% of the cylinder's rated capacity

Recovery cylinders must not be filled beyond 80% of their rated capacity to allow for liquid refrigerant expansion with temperature changes.

What is the term for the condition where chemical contaminants from one area migrate into another area through HVAC ductwork or building pressurization?

Answer: Cross-contamination

Cross-contamination occurs when airborne pollutants from one zone — such as a copy room or lab — migrate through shared HVAC systems into occupied spaces.

What is the purpose of a heat exchanger when connecting a hydronic loop to a pool or snowmelt slab?

Answer: To provide thermal and hydraulic isolation between loops with different water quality, chemicals, or pressure ratings

A plate heat exchanger separates the primary heating loop from secondary loops that may contain different chemicals or operate at different pressures, while efficiently transferring heat.

In a variable air volume (VAV) system, what happens to the outdoor air fraction when supply airflow decreases at part-load conditions?

Answer: The outdoor air fraction increases if outdoor air is fixed in volume

If the outdoor air volume is fixed (not reset), reducing total supply airflow at part load increases the outdoor air fraction, which can cause overcooling or excess humidity issues.

Which approach is recommended for troubleshooting system design issues?

Answer: Use systematic isolation and testing methods

Systematic isolation and testing methodically narrows down the root cause, making troubleshooting efficient and accurate.

Which professional attribute is most valued in ductwork within the HVAC field?

Answer: Accountability and commitment to standards

Accountability and commitment to professional standards build trust and ensure consistent, high-quality practice.

A technician discovers that a customer's existing refrigerant lines contain R-22. Which statement about handling this refrigerant is CORRECT?

Answer: R-22 must be recovered using EPA Section 608-certified equipment

EPA Section 608 prohibits venting R-22 and requires recovery using certified equipment; R-22 production ended in 2020 but existing supplies must still be properly handled.

What is the 'breathing zone' as defined by ASHRAE 62.1?

Answer: The region within an occupied space between 3 and 72 inches above the floor and more than 2 feet from walls—where occupants breathe

ASHRAE 62.1 defines the breathing zone as 3-72 inches above floor level, more than 2 feet from walls or fixed HVAC equipment—this zone must meet ventilation rate requirements.