You are about to braze the joints on a new line set for an R-410A split system. How should the nitrogen purge be set up?

A low flow of dry nitrogen through the line with the far end open to vent, maintained while each joint is heated

A quick blast of nitrogen through the line before brazing, then the line capped to keep it in

Nitrogen at 100 psig (690 kPa) held in the sealed line set so the joint is tested as it is brazed

No purge is needed on R-410A line sets because BCuP alloys are self-fluxing

Where should the micron gauge be connected so that it reads the true system pressure during the evacuation of a split system and in the decay test with the pump valved off?

On the system, at a port away from the pump connection

On the system, on a tee at the port the pump hose uses

At the vacuum pump's inlet, where the gauge responds fastest

On the manifold's centre hose, where one gauge sees pump and system

Which zoning method supplies air at a fixed temperature, throttles a damper at each zone terminal to match that zone's load, and lets the supply fan ride a duct static-pressure setpoint?

Constant-volume terminal reheat

When assembling a heat-pump reversing valve into the circuit, which tube connects to the compressor discharge?

The single tube on one side of the valve body.

The centre tube of the three on the other side.

The tube nearest the solenoid coil.

Either outer tube of the three; they are interchangeable.

Insulated suction lines are being hung on clevis hangers. What is placed at each hanger?

A shield or saddle (or a rigid insert) so the insulation and its vapour barrier are not crushed.

A rubber strip between hanger and copper, with the insulation cut away.

Nothing; the insulation is stiff enough to carry the line.

The hanger directly on the copper, with the insulation cut away at each support.

When reading a P/T chart for a zeotropic blend such as R-407C or R-448A, which column is used for superheat and which for subcooling?

Dew point for superheat; bubble point for subcooling

Either column; the glide is small enough to ignore on all blends

Bubble point for superheat; dew point for subcooling

The average of the two columns for both readings

How should the high-pressure safety switch on a new air-cooled condensing unit be proven at commissioning?

With gauges on, block condenser airflow and confirm the trip point and reset

Lower the set point until it trips at running pressure, then leave it there as the new setting

Check the switch contacts for continuity with an ohmmeter and record that they are closed

Remove it and bench-test it with regulated nitrogen to read its opening point

A rooftop unit's aluminum-fin condenser coil is heavily fouled with cottonwood seed and road dust. How should it be cleaned?

Brush off debris, apply an approved cleaner and rinse from the clean side at low pressure

Brush and vacuum the outside face only; liquid cleaners corrode aluminum fins

Pressure-wash the outside face at full pressure to drive the packed debris through the coil

Apply an acid coil brightener to cut the road film, then rinse from the clean side

A laboratory ultra-low freezer holding −80 °C (−112 °F) uses a cascade refrigeration system. What is the defining feature of a cascade system?

Two separate refrigerant circuits joined by an interstage heat exchanger

Two compressors piped in parallel on a common suction header

A single circuit with a secondary glycol loop for distribution

One refrigerant compressed in two stages by two compressors in series

10 Free Red Seal 313A Refrigeration & AC Questions + PDF

Ten 313A Refrigeration & AC Systems Mechanic questions in the format of the Red Seal exam: four options, one correct answer, no trick questions. They are free to use, print and share. There is nothing to sign up for on this page.

01How to use these

The questions come from the TicketPrep 313A bank and are spread across the exam's work activities in the order and roughly the proportion the Red Seal Program publishes for this trade: A (performs common occupational skills), B (performs routine trade activities), C (plans installation), D (performs installation), E (performs commissioning), F (performs maintenance and service). Answer each one before opening the explanation. Every explanation covers all four options, because, in the Red Seal Program's words, the incorrect options on the exam are not always obvious, and knowing why they are wrong is most of the skill.

Pace. The Red Seal Exam Preparation Guide gives four hours of writing time; for the 125 questions on this exam that is about 1 min 55 s per question. Try these at that pace.
Print. The printed version shows the questions and the answer key without the explanations, so it works as a handout. The explanations are on the web page. Download PDF
Mark. The Red Seal Exam Preparation Guide gives the pass mark as 70 percent; seven of ten here is the same bar.

02The questions

Recall · Performs common occupational skills

When setting up an oxy-acetylene brazing outfit, what is the maximum acetylene working pressure that should ever be set at the regulator?
1. 34 kPa (5 psig)
2. 103 kPa (15 psig)
3. 690 kPa (100 psig)
4. 207 kPa (30 psig)
Show the answer

B. Correct. Above about 103 kPa (15 psig) free acetylene becomes unstable and can decompose explosively without any oxygen present, so regulators are set at or below this value regardless of tip size. Related rules: keep acetylene cylinders upright (the gas is dissolved in acetone), withdraw no more than one-seventh of the cylinder's capacity per hour, and check the regulator gauges, hoses and flashback arrestors before lighting up.

Why not the others

A. About 34 kPa (5 psig) is a common working setting for small brazing tips, but it is a tip setting, not the limit. The safety limit for free acetylene is 103 kPa (15 psig).

C. This is in the range of a nitrogen purge or pressure-test setting, and would be catastrophic with acetylene. The acetylene limit is 103 kPa (15 psig).

D. This is in the range of an oxygen setting for a cutting tip, not an acetylene limit; brazing tips run at much lower oxygen pressures. The two gases have very different limits, and acetylene above 103 kPa (15 psig) is unstable.

Source: Red Seal Occupational Standard, sub-task A-2.03
Procedural · Performs routine trade activities

You are about to braze the joints on a new line set for an R-410A split system. How should the nitrogen purge be set up?
1. A quick blast of nitrogen through the line before brazing, then the line capped to keep it in
2. A low flow of dry nitrogen through the line with the far end open to vent, maintained while each joint is heated
3. Nitrogen at 100 psig (690 kPa) held in the sealed line set so the joint is tested as it is brazed
4. No purge is needed on R-410A line sets because BCuP alloys are self-fluxing
Show the answer

B. Correct. The purge displaces the oxygen inside the tube so that the heat does not form cupric-oxide scale on the inner wall. It is a gentle flow (about 1 to 2 L/min, 2 to 4 ft³/h) through a regulator, entering one end and leaving through an open port at the other, kept flowing until the joint has cooled below the oxidizing temperature. The purge is started before the torch is lit, because scale forms as soon as the inside of the copper reaches oxidizing temperature.

Why not the others

A. A blast does not keep the tube oxygen-free once the caps are on and the copper heats; air is drawn in as the gas expands and contracts. The purge must flow while the joint is heated.

C. Pressure inside the joint blows the molten filler out and leaves pinholes. Brazing is done at near-atmospheric pressure with a flowing purge; the pressure test comes after the joints are complete and cool.

D. Self-fluxing describes the outside of the joint, where the phosphorus deals with copper oxide. Inside the tube the heat still forms black scale unless the oxygen is displaced. The scale later plugs the TXV screen and the drier.

Source: Red Seal Occupational Standard, sub-task B-6.01
Procedural · Performs routine trade activities

Where should the micron gauge be connected so that it reads the true system pressure during the evacuation of a split system and in the decay test with the pump valved off?
1. On the system, on a tee at the port the pump hose uses
2. At the vacuum pump's inlet, where the gauge responds fastest
3. On the system, at a port away from the pump connection
4. On the manifold's centre hose, where one gauge sees pump and system
Show the answer

C. Correct. The gauge must read the pressure in the system, not in the pump. Connected at a system port remote from the pump hose, it sees the true system pressure; with the pump isolated by a valve, any rise is the system's own (leak or moisture), not pump performance. Reading at the pump shows the pump's vacuum while the system may still be thousands of microns higher.

Why not the others

A. This is on the system, but right where the pump draws: while the pump runs, gas flowing toward the hose makes the gauge read lower than the rest of the system, so the evacuation looks finished too soon. A port away from the pump connection reads the system itself.

B. The pump inlet is the lowest pressure in the whole set-up and can read a few hundred microns while the far end of the system is still at several thousand. It measures the pump, not the system.

D. The centre hose is in the pumping path: while the pump runs it reads near the pump's vacuum, lower than the system at the far end of the hoses, and in the decay test it also measures the manifold and hoses, whose own leaks and outgassing get blamed on the system.

Source: Red Seal Occupational Standard, sub-task B-6.03
Recall · Plans installation

Which zoning method supplies air at a fixed temperature, throttles a damper at each zone terminal to match that zone's load, and lets the supply fan ride a duct static-pressure setpoint?
1. Constant-volume terminal reheat
2. Multizone (hot and cold deck)
3. Variable air volume
4. Dual duct
Show the answer

C. Correct. A VAV system supplies cool air at a fixed temperature (about 13 °C / 55 °F) and each zone's terminal damper throttles airflow to match the load, with the supply fan riding a static-pressure setpoint. It saves fan energy at part load; perimeter zones usually add reheat or a separate heating system.

Why not the others

A. Terminal reheat delivers constant-volume cold air and reheats it at each zone to the temperature the zone wants. Temperature, not volume, is the variable.

B. A multizone unit mixes hot-deck and cold-deck air at the unit through a damper pair for each zone and sends it down that zone's duct. Each zone gets a constant volume at a varying temperature; there are no zone terminal dampers throttling flow.

D. A dual-duct system runs hot and cold decks to every zone and a mixing box blends them at the zone; airflow is constant and temperature varies. It is flexible but energy-intensive.

Source: Red Seal Occupational Standard, sub-task C-7.03
Procedural · Performs installation

When assembling a heat-pump reversing valve into the circuit, which tube connects to the compressor discharge?
1. The centre tube of the three on the other side.
2. The tube nearest the solenoid coil.
3. Either outer tube of the three; they are interchangeable.
4. The single tube on one side of the valve body.
Show the answer

D. Correct. The lone port on one side is the hot-gas inlet from the compressor discharge. On the opposite side, the centre tube of the three goes to the compressor suction, and the two outer tubes go to the indoor and outdoor coils; which outer tube serves which coil follows the manufacturer's piping diagram and the O/B energize convention. Wrap the valve body when brazing so the slide and seals are not heat-damaged.

Why not the others

A. The centre of the three is the suction connection back to the compressor. Putting discharge there would pump hot gas into the suction and the valve slide would never shift correctly.

B. The pilot solenoid sits on top of the valve and its position says nothing about the port function. Identify ports by the single-versus-three layout, not by the coil.

C. The outer tubes connect to the two coils, not to the compressor. They are not fully interchangeable either: the manufacturer's diagram assigns indoor and outdoor coil to match the valve's energized position.

Source: Red Seal Occupational Standard, sub-task D-9.02
Procedural · Performs installation

Insulated suction lines are being hung on clevis hangers. What is placed at each hanger?
1. A shield or saddle (or a rigid insert) so the insulation and its vapour barrier are not crushed.
2. A rubber strip between hanger and copper, with the insulation cut away.
3. Nothing; the insulation is stiff enough to carry the line.
4. The hanger directly on the copper, with the insulation cut away at each support.
Show the answer

A. Correct. The hanger must bear on something that spreads the load: a sheet-metal shield or saddle over the insulation, or a rigid high-density insert at the hanger point with the shield outside it. Crushed elastomeric insulation loses thickness and its vapour seal, and the line sweats and ices at every hanger. The saddle length grows with pipe size per the insulation manufacturer's table.

Why not the others

B. The rubber addresses galvanic contact but still leaves an uninsulated gap that sweats. Continuous insulation with a shield is the answer.

C. Closed-cell insulation compresses under a loaded clevis and stays compressed. The line ends up sitting on a thin, wet strip of foam.

D. Bare copper at every hanger is a cold spot that sweats and, on a low-temperature line, ices; the vapour barrier is broken at each gap. Insulation runs continuous through the hanger.

Source: Red Seal Occupational Standard, sub-task D-9.04
Recall · Performs commissioning

When reading a P/T chart for a zeotropic blend such as R-407C or R-448A, which column is used for superheat and which for subcooling?
1. Dew point for superheat; bubble point for subcooling
2. Either column; the glide is small enough to ignore on all blends
3. Bubble point for superheat; dew point for subcooling
4. The average of the two columns for both readings
Show the answer

A. Correct. A zeotropic blend evaporates and condenses over a temperature glide. Superheat begins once the last drop of liquid evaporates, which is the dew point, so suction-side superheat uses the dew-point column. Subcooling begins once the last bubble of vapour condenses, which is the bubble point, so liquid-side subcooling uses the bubble-point column. Using the wrong column mis-states the reading by the full glide.

Why not the others

B. That is roughly true for near-azeotropes such as R-410A, but R-407C and the R-448A/R-449A family have glides of several kelvin. On those blends the column choice changes the superheat or subcooling reading materially.

C. Reversed. The dew point is where the vapour is just saturated (end of evaporation), so it anchors superheat; the bubble point is where the liquid is just saturated (end of condensation), so it anchors subcooling.

D. Averaging discards the information the chart gives you and introduces an error of half the glide in each reading. Each side of the system has its own correct column.

Source: Red Seal Occupational Standard, sub-task E-11.03
Procedural · Performs commissioning

How should the high-pressure safety switch on a new air-cooled condensing unit be proven at commissioning?
1. With gauges on, block condenser airflow and confirm the trip point and reset
2. Lower the set point until it trips at running pressure, then leave it there as the new setting
3. Check the switch contacts for continuity with an ohmmeter and record that they are closed
4. Remove it and bench-test it with regulated nitrogen to read its opening point
Show the answer

A. Correct. A safety is proven only by producing the out-of-range condition and watching the control act. Raise head pressure in a controlled way (block airflow or interrupt the fan) while watching the high-side gauge, note the trip point against the manufacturer's setting, confirm the compressor stops and that the manual or automatic reset behaves as specified, then restore airflow. Never let the pressure approach the relief-valve setting.

Why not the others

B. That proves the contacts work but leaves the switch set far below the manufacturer's value, so the unit trips on every hot day. After a trip test the control is returned to the specified setting.

C. Closed contacts at normal pressure prove only that the switch is not open now. A safety must be shown to open at its set point; that requires reaching the set point.

D. A bench test reads the switch's opening point but leaves the installed circuit unproven: whether the compressor actually stops and whether the reset behaves as specified are only shown by tripping it in place, on the running unit.

Source: Red Seal Occupational Standard, sub-task E-12.02
Procedural · Performs maintenance and service

A rooftop unit's aluminum-fin condenser coil is heavily fouled with cottonwood seed and road dust. How should it be cleaned?
1. Brush and vacuum the outside face only; liquid cleaners corrode aluminum fins
2. Pressure-wash the outside face at full pressure to drive the packed debris through the coil
3. Brush off debris, apply an approved cleaner and rinse from the clean side at low pressure
4. Apply an acid coil brightener to cut the road film, then rinse from the clean side
Show the answer

C. Correct. Cleaning follows the manufacturer's cleaner recommendation (non-acid on aluminum and microchannel), rinsing from the clean side so dirt is pushed out the way it came in, and low pressure so the fins are not bent. A cleaner not compatible with the coil metals corrodes the thin fins and tubes and shortens coil life.

Why not the others

A. Dry brushing lifts the surface mat of seed fluff but leaves road film and dirt packed between the fins and through the coil depth. A non-acid cleaner approved for the coil is made for this, followed by a low-pressure rinse from the clean side.

B. Full-pressure washing from the dirty side drives debris deeper into the coil and flattens fins. Rinse from the clean side at low pressure.

D. Acid brighteners etch thin aluminum fins and attack the fin-to-tube bond, shortening coil life. The cleaner is the non-acid one the coil manufacturer approves; the rinse direction is right, the chemical is not.

Source: Red Seal Occupational Standard, sub-task F-13.02
Recall · Performs maintenance and service

A laboratory ultra-low freezer holding −80 °C (−112 °F) uses a cascade refrigeration system. What is the defining feature of a cascade system?
1. Two compressors piped in parallel on a common suction header
2. A single circuit with a secondary glycol loop for distribution
3. Two separate refrigerant circuits joined by an interstage heat exchanger
4. One refrigerant compressed in two stages by two compressors in series
Show the answer

C. Correct. The low-stage circuit uses a refrigerant suited to very low temperatures, and its condenser is cooled by the evaporator of the high-stage circuit in a cascade (interstage) heat exchanger. Each stage keeps a manageable compression ratio.

Why not the others

A. That is a parallel rack, used for capacity control in supermarkets. It does not reach ultra-low temperatures on its own.

B. A secondary loop moves cooling with a brine or glycol; it is not a second refrigeration stage. Cascade systems use two vapour-compression circuits.

D. That describes a compound system: one refrigerant, two stages of compression with an intercooler. A cascade uses two separate refrigerant circuits.

Source: Red Seal Occupational Standard, sub-task F-14.01

03Answer key

Question	Answer	Work activity
Q1	B	Performs common occupational skills
Q2	B	Performs routine trade activities
Q3	C	Performs routine trade activities
Q4	C	Plans installation
Q5	D	Performs installation
Q6	A	Performs installation
Q7	A	Performs commissioning
Q8	A	Performs commissioning
Q9	C	Performs maintenance and service
Q10	C	Performs maintenance and service

04More free questions

For the 313A exam itself, the 313A exam guide covers the work activities, their weights and how the exam is scored, and the 313A Refrigeration & AC Systems Mechanic practice exam page describes the full TicketPrep 313A question bank. The same free format is available for the other 17 trades, plus the free guides on the pass mark, question counts, exam day and how to study.

How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.

05Questions by exam block

Working on one part of the 313A exam? Each block has its own page with five more free questions, the tasks the block covers and their weights.