313D Certificate of Qualification · Ontario

313D Practice Exam: Residential Air Conditioning Systems Mechanic (Ontario C of Q)

Five original 313D exam questions to start, from four of the six skill sets: service clearances at a townhouse condensing unit, a liquid-line restriction under a deck, the record that proves a warranty's maintenance condition, a fan motor's power factor and the currents on a PSC compressor. Whether you are finishing a 313D apprenticeship or writing the 313D challenge exam after a Trade Equivalency Assessment, pick an answer, then open the explanation. Every question in the bank explains all four options, not just the right one.

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63 free 313D questions in all

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A residential air conditioning mechanic in safety glasses and gloves connecting a digital manifold to an outdoor heat pump beside a house's siding — Field study313D Residential AC

Critical thinking · Skill set B · Assemble and Install

The manual for a townhouse condensing unit requires at least 300 mm (12 in.) from walls on its coil sides, 610 mm (24 in.) clear in front of the service panel and 1 520 mm (60 in.) clear above the fan. At the proposed spot: coil side to house wall 330 mm (13 in.), coil side to fence 305 mm (12 in.), service panel to a deck post 455 mm (18 in.), open sky above. Which measurement rules the spot out?
1. The open clearance above the fan discharge.
2. The coil-side clearance to the privacy fence.
3. The coil-side clearance to the house wall.
4. The service panel clearance to the deck post.
Show the answer
D. Correct. 455 mm (18 in.) is 155 mm (6 in.) short of the 610 mm (24 in.) the manual requires in front of the service panel; the other three meet their minimums, so the unit moves or the post does.
Source: STO 313D counselling sheet, skill set B: Assemble and Install (our sub-task B-5.01)
Critical thinking · Skill set D · Service

An R-410A piston system will not cool; its line set runs 9 m (30 ft) from the outdoor unit, under a deck, to the house wall. At 29 °C (84 °F): suction 605 kPa (88 psig), dew −3.7 °C; suction line 11.5 °C; liquid 2 000 kPa (290 psig), bubble 34.2 °C. Liquid-line temperatures: drier inlet and outlet 26.0 °C, service valve 26.0 °C, at the house wall 9.0 °C (sweating), at the coil 8.0 °C. Where is the fault?
1. In the filter-drier at the outdoor unit.
2. In the liquid line under the deck.
3. In the piston at the indoor coil.
4. In the coil's distributor tubes.
Show the answer
B. Correct. Liquid should stay near 26 °C all the way to the piston. It falls to 9.0 °C between the service valve and the wall, so pressure is lost there and the liquid flashes: the line is kinked or crushed under the deck. Superheat 11.5 − (−3.7) = 15.2 K with subcooling 34.2 − 26.0 = 8.2 K is the restriction pattern.
Source: STO 313D counselling sheet, skill set D: Service (our sub-task D-14.02)
Procedural · Skill set E · Maintain

A client's four-year-old heat pump has a failed compressor. The maker's warranty, as the client's papers state it, covers the compressor only if the unit has had a maintenance visit every year. Which record shows that this condition was met?
1. The original installation invoice, which shows the date the unit went in.
2. Dated work orders for each yearly visit, naming the unit's serial number.
3. The thermostat's run-time log, which shows the unit was used normally.
4. Receipts for the replacement filters the client has bought and fitted.
Show the answer
B. Correct. A warranty that depends on yearly maintenance is proved by records of that maintenance: a dated work order for each visit naming the unit (model and serial number), what was done and the readings taken. Keeping these records, with a copy for the client, is part of every maintenance visit.
Source: STO 313D counselling sheet, skill set E: Maintain (our sub-task E-18.01)
Procedural · Skill set F · Service or Maintain Electrical Components

At the outdoor fan motor of a heat pump a wattmeter reads 270 W, a clamp meter 1.5 A and a voltmeter 240 V. Power factor is true power divided by apparent power (volts × amps). What is the motor's power factor?
1. 0.38
2. 0.43
3. 0.75
4. 1.33
Show the answer
C. Correct. Apparent power = 240 V × 1.5 A = 360 VA; power factor = 270 W ÷ 360 VA = 0.75. An induction fan motor draws magnetizing current that does no work, so its watts are less than its volts × amps, and only a wattmeter shows the power it uses.
Source: STO 313D counselling sheet, skill set F: Service or Maintain Electrical Components (our sub-task F-23.01)
Critical thinking · Skill set F · Service or Maintain Electrical Components

On a running PSC compressor the clamp meter reads 11.2 A on the run lead, 4.6 A on the start lead and 12.0 A on the common lead. A trainee expects the common to read 15.8 A and suspects the meter. What explains the readings?
1. The two winding currents are out of phase, so they add to less.
2. The meter is faulty, so the common lead must be read again.
3. The run capacitor is shorted, so some current bypasses the common.
4. The common terminal is loose, so it passes less of the current.
Show the answer
A. Correct. The run capacitor makes the start-winding current lead the run-winding current by close to 90°, so the two add as vectors, not as plain numbers. Here √(11.2² + 4.6²) = 12.1 A, close to the 12.0 A on the common: the readings agree and the motor is behaving as designed.
Source: STO 313D counselling sheet, skill set F: Service or Maintain Electrical Components (our sub-task F-23.02)

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Want ten more with every option explained? Free 313D Residential AC practice questions: no account, no email, printable (PDF). With eight more on each skill-set page below, that makes 63 free 313D questions in all.

The 313D exam at a glance

How many questions are on the 313D exam?

Skilled Trades Ontario (STO) does not publish a question count for the 313D exam. Its training standard and its Exam Prep Guide say only that its certifying exams have between 90 and 150 multiple-choice questions, with up to four hours to write, and its 313D exam counselling sheet sets the pass mark at 70%. Our timed mock exam is 130 questions in four hours; 130 is our own number, chosen inside STO's range. Sources: STO's 313D trade page, with the counselling sheet and training standard, and its Exam Prep Guide (June 2026) (read November 1, 2026).

Pass mark: 70 %
Time: Up to 4 h
Skill sets: 6 weighted
Our bank: 550

313D is Ontario's Residential Air Conditioning Systems Mechanic trade, and it is compulsory: to work in it you need a registered training agreement, a provisional Certificate of Qualification or a Certificate of Qualification (C of Q). STO sets and delivers the certifying exam, and passing it is how you get the C of Q, whether you come from a 313D apprenticeship or challenge the exam after a Trade Equivalency Assessment. 313D is not a Red Seal trade. Its Red Seal sister trade is 313A Refrigeration and Air Conditioning Systems Mechanic, the full trade; 313A vs 313D sets out the difference.

The weights come with a date. STO's 313D exam counselling sheet weights six skill sets, from Plan and Prepare at 7% to Assemble and Install, Service and Maintain at 21% each. The sheet's body says “Updated as of December 5, 2016”, and its skill sets follow the older (2003) training standard. The current training standard, in force since December 4, 2023, regroups the skill sets, so the weights may not match today's exam. They are still the only weights STO publishes for 313D, so our mock exams follow them.

Since February 1, 2026 STO delivers its certifying exams itself, at STO exam centres and on-site at some training providers, on paper or on screen as your exam confirmation says; there is no online option. The fee is $150 + HST, and results come within 15 business days. If you do not pass, you wait 30 days and pay the fee again before you rewrite. STO does not say whether the 313D exam is open book; its Exam Prep Guide asks you to bring government-issued photo ID and keeps phones, watches and smart devices out of the room. The 313D exam guide has the details.

The full 313D practice exam

Find out where you stand on all six skill sets.

550 original practice questions for the 313D exam, 400 Standard and 150 Advanced, across all six skill sets on STO's counselling sheet, with the reason for every option. Timed mock exams of 130 questions in four hours, drawn 9, 27, 13, 28, 27 and 26 from skill sets A to F in proportion to the sheet's weights, and scored against the 70% pass mark with your score on each skill set, so a weak one shows up before exam day.

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Also writing 313A or another exam on TicketPrep? All-Access covers 313D for $119, with 313A and every other exam on the site included.

What the 313D exam covers

Six skill sets, weighted by STO's counselling sheet.

The table gives the counselling sheet's weight for each skill set and how many questions each gets in our 130-question mock. The mock counts are ours: the sheet's percentages scaled to 130, not an STO figure. STO publishes no 313D question count, and the sheet is dated 2016, so treat the weights as a guide to where the marks are, not a promise of today's paper.

Skill set	Counselling sheet title (short)	Sheet weight	Our mock (of 130)
A	Plan and Prepare	7%	9
B	Assemble and Install	21%	27
C	Commission	10%	13
D	Service	21%	28
E	Maintain	21%	27
F	Service or Maintain Electrical Components	20%	26
	Total	100%	130

Weights: STO's Residential Air Conditioning Systems Mechanic 313D exam counselling sheet (body “Updated as of December 5, 2016”). The sheet leaves safety, customer service and tools unweighted; our bank folds them into the six skill sets. Our 313D study blueprint (PDF) lists every task and sub-task we wrote to.

A
Plan and Prepare · 7% · 38 in our bank
Reading work orders, house drawings and installation manuals; permits and other trades inside the 313D scope; room-by-room heat loss and gain in outline, psychrometrics, and matching equipment to the load and the 313D limits; choosing the system, controls and refrigerant-circuit accessories. Free skill set A questions: plan and prepare →
B
Assemble and Install · 21% · 109 in our bank
Receiving equipment and evaluating the site, setting the units, flaring, brazing and running the line set, the nitrogen pressure test, evacuation and charging a new system, ductless and multi-zone heat pumps, condensate and indoor air quality accessories, and the branch circuit and low-voltage wiring. Free skill set B questions: assemble and install →
C
Commission · 10% · 60 in our bank
Pre-start checks, setting and testing the controls, verifying airflow and the charge by superheat or subcooling, recording readings against the nameplate and manual, and handing the system over. Free skill set C questions: commissioning →
D
Service · 21% · 124 in our bank
Running a service call and diagnosing refrigerant-circuit, heat-pump, ductless and inverter faults from readings; recovery and decommissioning; replacing compressors, metering devices, reversing valves and driers; finding leaks; and repairing blowers, zoning and coils. Free skill set D questions: service and troubleshooting →
E
Maintain · 21% · 99 in our bank
Inspecting, recording and advising the client; seasonal start-up and shut-down; filters, coils, blowers and ducts; condensate, humidifiers, HRVs and ERVs; and leak and charge checks under the refrigerant rules. Free skill set E questions: maintenance →
F
Service or Maintain Electrical Components · 20% · 120 in our bank
Circuits, meters and safe testing; compressor motors, capacitors, fan motors and ECMs; contactors, relays, transformers and protective devices; thermostats, safety controls, sequences of operation and zone controls; sensors and inverter drives; wiring repairs and electric heat. Free skill set F questions: electrical and controls →

Where our questions come from

Every question original, every one inside the 313D scope.

The 28 tasks and 70 sub-tasks in our 313D bank are our own grouping, written from public sources: STO's counselling sheet for the six skill sets and their weights; the 313D training standard (in force since December 4, 2023) and the 313A and 313D curriculum standards, read for what they cover and never reproduced; and Ontario's regulations on e-Laws, with the scope of the trade in O. Reg. 875/21 and the refrigerant rules in O. Reg. 463/10. Questions that rest on CSA B52, CSA F280 or the Ontario Electrical Safety Code explain the requirement in their own words and cite the standard by name; we never reproduce their text or tables. Every question stays inside the scope O. Reg. 875/21 s. 119 sets for the trade: an independent unit in a residential family dwelling, at no more than 240 volts single phase, a 60 amp branch circuit and 60,000 Btu/h of cooling. Every question went through a separate, blind verification pass in which every calculation is recomputed. Nothing is copied from courses, workbooks or recalled exam questions. For the exam format, the fees and the licence route, read the 313D exam guide and how to get your 313D licence. Read how our questions are made.

Edited by Trevor Mulder · Last checked November 1, 2026 against Skilled Trades Ontario's 313D trade page, its exam counselling sheet, its Exam Prep Guide (June 2026) and O. Reg. 875/21.

Why practice scores mislead

Knowing the parts is not the same as reading the numbers.

Many of our 313D questions hand you a set of readings and ask what they mean. A liquid line that sweats at the house wall, a common lead that reads less than the run and start leads added together, a service clearance 155 mm short: each is one reading among several normal ones. Knowing what a filter-drier or a run capacitor does will not find it for you. Our explanations give the reason and the arithmetic behind every option, and our mock exams put 130 questions in front of you in four hours, weighted to the counselling sheet, so you find out which skill sets hold up under time, not just your average.

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How TicketPrep prepares you

Built like a study tool, not a quiz app.

All six skill sets

Every skill set on STO's counselling sheet and every one of the 70 sub-tasks we wrote for them, at Standard and Advanced levels.

Every answer explained

Why the right answer is right, and why each of the other three is wrong, with the arithmetic shown on every calculation.

Timed mock exams

130 questions in four hours, drawn 9, 27, 13, 28, 27 and 26 from skill sets A to F. STO publishes no 313D question count, so the 130 and the split are ours.

Inside the 313D scope

Residential split systems, heat pumps and ductless units within O. Reg. 875/21 s. 119: no commercial refrigeration, no three-phase power, no gas-side work.

313D exam questions

Before you start.

How many questions are on the 313D exam?

Skilled Trades Ontario does not publish a question count for the 313D exam. Its training standard and Exam Prep Guide say only that its certifying exams have between 90 and 150 multiple-choice questions, each with four options, and up to four hours to write. Our timed mock exam is 130 questions in four hours: 130 is our own number, inside STO's range, not a figure STO has given for 313D.

What is the pass mark for the 313D exam?

70 percent. STO's 313D exam counselling sheet gives a pass mark of 70%, and its Exam Prep Guide gives the same passing grade for its certifying exams. No per-skill-set minimum is published, so our mock exams score the whole paper against 70 percent and show your result on each skill set.

What is on the 313D exam?

STO's counselling sheet weights six skill sets: Plan and Prepare 7%, Assemble and Install 21%, Commission 10%, Service 21%, Maintain 21%, and Service or Maintain Electrical Components 20%. The sheet's body says it was updated as of December 5, 2016, and it follows the 2003 training standard; the current standard, in force since December 4, 2023, regroups the skill sets, so the weights may not match today's exam. Our 130-question mock draws 9, 27, 13, 28, 27 and 26 questions from them.

Can I write the 313D challenge exam without an apprenticeship?

Yes, if you qualify. Experienced workers who did not finish an Ontario apprenticeship start with STO's Trade Equivalency Assessment, which costs $235 + HST and decides whether you may challenge the certifying exam; STO looks for experience at least equal to the apprenticeship's total training time, which for 313D is 4,500 hours. If you are approved, you book the same exam as apprentices, for $150 + HST.

Is 313D a Red Seal trade?

No. 313D Residential Air Conditioning Systems Mechanic is an Ontario-only compulsory trade with its own provincial Certificate of Qualification exam. Its sister trade, 313A Refrigeration and Air Conditioning Systems Mechanic, is the Red Seal trade, with the full scope of the trade and a 9,000-hour apprenticeship against 313D's 4,500 hours.

Is the 313D practice exam free?

Yes, to start. You can try five free questions in the quiz with no account, and read 63 more with answers on this site: five on this page, ten on the free questions page and eight on each skill-set page. The full 550-question bank, 400 Standard plus 150 Advanced, and the timed mock exams come with Exam Pass, a one-time $69 purchase for 120 days of access, not a subscription. All-Access, $119, covers 313D, 313A and every other exam on TicketPrep.

Are these questions from the 313D exam?

No. Every question is original, written by TicketPrep from STO's public counselling sheet, the coverage of the 313D training standard and Ontario's regulations, and none is a recalled or shared exam question. STO publishes no official sample questions for its provincial trades, and its exam integrity policy treats capturing or sharing exam content as misconduct, so no practice bank, ours included, comes from STO. TicketPrep is not affiliated with Skilled Trades Ontario or CSA Group.

What if I fail the 313D exam?

STO publishes results within 15 business days. If you do not pass, there is a mandatory 30-day waiting period before you can write it again, and you pay the $150 + HST exam fee again before you rebook. With Exam Pass, if you write the 313D exam and don't pass, you get 120 more days of access free.

Find out where you actually stand.

Five free questions. No account and no email to start: you see right or wrong as you go and your score at the end. Your email is optional, only to unlock the written explanations. About five minutes.

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Then Exam Pass is $69 one-time for 120 days of access, not a subscription, with a 7-day money-back guarantee. Write the 313D exam and don't pass? You get 120 more days free. All-Access covers 313D, 313A and every other exam on TicketPrep for $119.

Also on TicketPrep

The 313D exam guide, the licence route, ten more free questions, and the 313A sister trade.

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