Mixed Deck — All 313A Topics Flashcards

In Canadian HVAC wiring, what voltage is most commonly used for low-voltage control circuits?

Answer: 24 V AC

24 V AC is the standard low-voltage control circuit voltage in Canadian and North American HVAC systems, provided by a step-down transformer from 120 V or 240 V.

Under Canadian ODSHAR regulations, what must technicians do with recovered refrigerant that cannot be reused?

Answer: Store it in an approved container and send it to a licensed refrigerant reclaimer or destruction facility

Intentional venting of controlled refrigerants is prohibited in Canada; recovered refrigerant that cannot be reused must be sent to a licensed reclaimer or destruction facility in approved containers.

What is the function of the suction accumulator in a refrigeration system?

Answer: To trap liquid refrigerant and oil returning to the compressor, allowing only vapour to enter

A suction accumulator is a reservoir installed in the suction line before the compressor. It catches and holds liquid refrigerant and oil that might otherwise enter the compressor, protecting it from liquid slugging. A small metering orifice at the bottom gradually returns oil and small amounts of liquid to the compressor.

What symptom would a restricted liquid line filter-drier produce in a refrigeration system?

Answer: Low suction pressure, high superheat, subcooling drop across the drier, and possibly a cold or frosted drier body

A restricted filter-drier creates a pressure drop across it, starving the expansion device of liquid — the result is low suction pressure, high superheat, a measurable subcooling temperature drop across the drier, and possibly frost on the drier body where pressure drops sharply.

When cutting copper refrigerant tubing, which tool provides the cleanest cut with the least internal deformation?

Answer: Wheel-type tubing cutter

A wheel-type tubing cutter produces a clean, square cut with only a small internal burr that is easily removed by reaming, while saws leave rough edges and metal filings.

What is the difference between a fin-and-tube evaporator and a plate evaporator?

Answer: A fin-and-tube uses tubes with attached fins for air-cooled applications; a plate evaporator uses stacked plates for liquid-cooled or direct-contact applications

Fin-and-tube evaporators use copper or aluminium tubes with aluminium fins pressed onto them to increase surface area for air-to-refrigerant heat exchange. Plate evaporators use corrugated stainless steel plates to create channels for refrigerant and the fluid being cooled, offering high efficiency in compact liquid-cooling applications.

What does a high suction pressure reading typically indicate in a refrigeration system?

Answer: High heat load or overcharge of refrigerant

High suction pressure usually indicates an excessive heat load on the evaporator or a refrigerant overcharge, both of which cause more refrigerant vapour to enter the compressor suction.

What is 'evaporator flooding' and what are its consequences?

Answer: Liquid refrigerant carrying over from the evaporator into the compressor suction, risking liquid slugging

Evaporator flooding occurs when the expansion device allows too much liquid refrigerant into the evaporator, and unevaporated liquid travels to the compressor suction, where it can cause liquid slugging and compressor damage.

What is the recommended method to confirm a refrigerant leak location after an electronic detector gives an alarm?

Answer: Apply an approved refrigerant-compatible leak detection solution (bubble solution) or use a UV dye and UV light to pinpoint the exact leak location

After an electronic detector alerts to a possible leak, bubble solution or UV dye with a UV lamp is used to pinpoint the exact location; UV dye that was pre-charged into the system glows brightly at the leak site under UV light.

What is the saturation temperature of a refrigerant?

Answer: The temperature at which the refrigerant changes state (boils or condenses) at a given pressure

Saturation temperature is the temperature at which a refrigerant changes between liquid and vapour states at a specific pressure. At saturation, liquid and vapour coexist. Every refrigerant has a unique pressure-temperature relationship that technicians use for system diagnosis.

What low-GWP refrigerant is being widely adopted as a replacement for R-410A in residential HVAC systems?

Answer: R-32

R-32 (difluoromethane) has a GWP of 675 — significantly lower than R-410A — and is being widely adopted as a more climate-friendly replacement for residential air conditioning globally, including in Canada.

Under Canadian OHS regulations, what is required before a technician enters a confined space that may contain refrigerant vapour?

Answer: A confined space entry permit, atmospheric testing for oxygen level, flammable gases, and toxic contaminants, and a standby person outside the space

Provincial OHS regulations across Canada require a formal confined space entry program including written permits, atmospheric testing (O2, flammable gas, toxic substances including refrigerants), and a trained attendant outside before any worker enters a confined space.

What is the purpose of a contactor in an HVAC electrical circuit?

Answer: To act as an electrically operated switch that uses a low-voltage control coil to open and close high-voltage power contacts to the compressor or fan motor

A contactor uses a low-voltage coil (typically 24V) energized by the control circuit to magnetically close heavy-duty power contacts, allowing full line voltage to energize loads like compressors and fan motors.

What is the purpose of a defrost timer in a refrigeration system?

Answer: To initiate defrost cycles at preset time intervals and terminate them after a set duration or when a termination thermostat trips

A defrost timer initiates defrost at programmed intervals (e.g., every 6 or 8 hours) and terminates the defrost cycle when a time limit or defrost termination thermostat setpoint is reached, then returns the system to normal cooling.

What is the purpose of a nitrogen purge when brazing refrigerant lines?

Answer: To displace oxygen inside the pipe during brazing, preventing oxide scale formation inside the copper tube that would contaminate the refrigerant system

Flowing dry nitrogen through the tubing during brazing displaces oxygen inside the pipe, preventing the formation of copper oxide scale (cupric oxide) that would otherwise flake off and contaminate the compressor valves and expansion devices.

What is the purpose of calculating the refrigeration effect in system design?

Answer: To determine how much heat the evaporator can absorb per kilogram of refrigerant

The refrigeration effect (kJ/kg) tells the designer how much heat each kilogram of refrigerant absorbs as it passes through the evaporator, which is used to size the system for the required cooling load.

Under Canadian regulations (Environmental Protection Act and provincial codes), what certification is required to purchase and handle refrigerants?

Answer: An ODP (Ozone Depletion Prevention) licence from the provincial authority and/or an Environmental Awareness Certificate for handling refrigerants

In Canada, technicians must hold valid certification to purchase, handle, and recover refrigerants. Requirements vary by province but generally include completion of an approved environmental awareness course and obtaining a certificate or licence from the provincial authority (e.g., TSSA in Ontario, BCSA in BC).

What is the purpose of a high-pressure safety switch (cutout) on a refrigeration system?

Answer: To shut off the compressor if discharge pressure exceeds a safe limit, preventing equipment damage or rupture

The high-pressure cutout is a safety device that opens the compressor control circuit if the discharge (head) pressure exceeds a predetermined setpoint. This protects against conditions such as condenser blockage, overcharge, non-condensable gases, or condenser fan failure that could cause dangerous pressures or compressor damage.

What is the purpose of a lockout-tagout (LOTO) procedure when servicing HVAC equipment in Canada?

Answer: To isolate and lock all energy sources (electrical, refrigerant pressure, etc.) to prevent unexpected re-energization during maintenance, protecting the technician from injury

LOTO procedures, required under provincial occupational health and safety (OHS) regulations across Canada, ensure that electrical power and other energy sources are isolated and locked before service work begins, preventing accidental startup.

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

Answer: To keep the compressor oil warm during off cycles, preventing refrigerant migration and liquid slugging on startup

A crankcase heater keeps the oil sump warm when the compressor is off. Without it, refrigerant can migrate to the cold compressor crankcase and mix with the oil. On startup, the sudden pressure drop would cause the liquid refrigerant to flash to vapour (foam), washing oil off bearings and causing potential liquid slugging.