The 313D exam is the certifying exam for Ontario's Residential Air Conditioning Systems Mechanic trade. Skilled Trades Ontario (STO) sets and delivers it, and passing it is how you get the trade's Certificate of Qualification (C of Q). STO's 313D exam counselling sheet sets the pass mark at 70 per cent and weights six skill sets, but the sheet is dated 2016 and follows the older training standard, so the weights may not match today's exam. STO publishes no 313D question count: it says only that its certifying exams have between 90 and 150 multiple-choice questions and up to four hours. The exam fee is $150 + HST, and after a fail you wait 30 days before you rewrite. 313D is an Ontario-only trade, not a Red Seal trade.
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01What is the 313D Certificate of Qualification?
Residential Air Conditioning Systems Mechanic, trade code 313D, is a compulsory trade in Ontario. STO's trade page puts it plainly: because the trade is compulsory, to practise it legally a person must hold a registered training agreement, a provisional Certificate of Qualification or a Certificate of Qualification, and appear on STO's Public Register. The C of Q is issued once you pass the certifying exam, and it must be renewed every year ($60 + HST).
The trade covers residential air conditioning and heat pump systems, within limits set in law. O. Reg. 875/21 s. 119 gives 313D the same scope as the full 313A trade, but "limited to" systems installed "as an independent unit in a residential family dwelling", at no more than 240 volts single phase, a 60 amp branch circuit, 60,000 Btu/h of cooling and a saturated suction temperature above 2 degrees Celsius (35 degrees Fahrenheit). Commercial refrigeration, three-phase equipment and larger systems fall outside 313D, within the wider 313A scope.
313D is not a Red Seal trade. Its sister trade, 313A Refrigeration and Air Conditioning Systems Mechanic, is the Red Seal trade; 313A vs 313D compares the two. STO's Fair Registration Practices report counts 3,637 313D certificate holders in 2025 and 246 new C of Qs that year. For the routes to the exam, apprenticeship or a Trade Equivalency Assessment, read how to get your 313D licence in Ontario.
02What is the 313D exam format?
STO publishes the format of its certifying exams in general terms, in its 313D training standard and in its Exam Prep Guide (June 2026):
- Multiple choice, with four options and one correct answer;
- between 90 and 150 questions, a range STO gives for its exams in general;
- up to four hours to write;
- paper based or electronic, as your exam confirmation email says.
STO does not publish how many questions the 313D exam itself has. Sites that quote an exact count are giving their own figure, and so are we: our mock exam is 130 questions, a number we chose inside STO's range. STO also publishes no official sample questions for its provincial trades.
Since February 1, 2026 STO delivers its certifying exams itself instead of through a contractor. You book through the STO Portal and write at an STO exam centre, part of a network of 24 partnerships with colleges and institutions across Ontario, or on-site at some training providers. There is no option to write from home.
03How is the 313D exam scored?
The pass mark is 70 per cent. STO's 313D exam counselling sheet says so, and its Exam Prep Guide gives the same passing grade. No minimum for each skill set is published, so the whole paper counts toward the 70 per cent.
STO says results are provided within 15 business days and published to your STO Portal account, with an email when they are posted.
04What do the six skill sets cover?
STO's counselling sheet names six skill sets and gives each a weight. The summaries below are our own reading of what each covers, written from the coverage of the training standard and the curriculum; they do not reproduce STO's text. The question counts are from our 130-question mock, the sheet's percentages scaled to 130, not STO figures.
Skill set A: Plan and Prepare
7 per cent on the sheet, 9 questions in our mock. Reading work orders, house drawings, wiring diagrams and the maker's installation manual; arranging permits, inspections and other trades within the 313D scope; room-by-room heat loss and heat gain in outline, psychrometrics for comfort cooling, and matching equipment to the load and to the 313D limits; and choosing the system type, controls and refrigerant-circuit accessories.
Free skill set A practice questions: Plan and Prepare →
Skill set B: Assemble and Install
21 per cent, 27 questions. Receiving equipment and evaluating the site, setting and supporting the indoor and outdoor units, cutting, flaring, brazing and running the line set, the nitrogen pressure test, evacuation and the first charge, ductless and multi-zone heat pumps, condensate disposal, indoor air quality accessories, and the branch circuit and low-voltage wiring.
Free skill set B practice questions: Assemble and Install →
Skill set C: Commission
10 per cent, 13 questions. Pre-start checks, setting and testing the controls, verifying airflow and the charge by superheat or subcooling, recording operating readings against the nameplate and manual, and handing the system over to the owner.
Free skill set C practice questions: Commission →
Skill set D: Service
21 per cent, 28 questions. Running a service call; diagnosing refrigerant-circuit, heat-pump, ductless and inverter faults from pressures, temperatures and amps; recovery and decommissioning; replacing compressors, metering devices, reversing valves, driers and service valves; finding and repairing leaks; and repairing blowers, zoning and coils.
Free skill set D practice questions: Service and Troubleshooting →
Skill set E: Maintain
21 per cent, 27 questions. Inspecting, recording and advising the client, seasonal start-up and shut-down, filters, coils, blowers and ducts, condensate systems, humidifiers, HRVs and ERVs, and leak and charge checks under Ontario's refrigerant rules.
Free skill set E practice questions: Maintain →
Skill set F: Service or Maintain Electrical Components
20 per cent, 26 questions. Circuits, meters and safe testing; compressor motors and their starting components, capacitors, fan motors and ECMs; contactors, relays, transformers, fuses and disconnects; thermostats, safety and operating controls, sequences of operation and zone controls; sensors and inverter drives; and wiring repairs and electric heat.
The sheet leaves three areas without a weight: safety, customer service and tools. They are still part of the trade, so expect them inside the weighted skill sets; our bank folds them in the same way.
Free skill set F practice questions: Electrical Components and Controls →
05Are the 2016 weights still current?
Nobody outside STO can say for certain. The counselling sheet on STO's site has 2023 in its file name, but its body says "Updated as of December 5, 2016", and its six skill sets follow the 2003 training standard. The current training standard, in force since December 4, 2023, regroups the trade into eight skill sets. The table shows how the sheet's headings line up with them.
| Sheet skill set | Weight | 2023 training standard | Our mock |
|---|---|---|---|
| A Plan and Prepare | 7% | 9120 Plan and Prepare | 9 |
| B Assemble and Install | 21% | 9121 Install | 27 |
| C Commission | 10% | 9124 Commission | 13 |
| D Service | 21% | 9123 Service | 28 |
| E Maintain | 21% | 9122 Maintain | 27 |
| F Service or Maintain Electrical Components | 20% | the electrical parts of 9122 and 9123 | 26 |
The 2023 standard also has three skill sets the sheet does not weight: protecting yourself, others and the environment; business practices; and tools and equipment. The headings match closely, so the weights are still the best guide STO publishes to where the marks are. Treat them as a guide, not as the exact make-up of the paper you will write.
06How do you book the 313D exam, and what does it cost?
You reach the exam by one of two routes. Apprentices write it at the end of the 313D apprenticeship. Experienced workers who did not apprentice in Ontario apply for STO's Trade Equivalency Assessment, which costs $235 + HST and decides whether you may challenge the exam.
Once you are eligible, you pay the exam fee of $150 + HST in your STO Portal account and book a sitting there (STO exam scheduling). If you need accommodation, ask before you book; STO says some requests need supporting documents.
07What do you bring, and is it open book?
STO's Exam Prep Guide asks you to bring government-issued photo identification and to read your exam confirmation notice. Cellphones, watches, hats, wallets and smart technology such as smart watches, glasses and headphones are not permitted in the exam room, and the conduct rules are read at the start of the exam.
STO does not state whether the 313D exam is open or closed book, and it states no formula sheet. Its Examination Integrity and Compromise policy lists possession or use of unauthorized paper, notes or calculations as misconduct, so take nothing in that your confirmation does not allow, and prepare to work the arithmetic from memory. If it matters to you, ask STO before exam day.
08Do you need an ODP card as well?
Yes. The C of Q and the ODP card are separate. Ontario's refrigerant regulation, O. Reg. 463/10, says in s. 22(1): "No person shall service or test refrigeration equipment that contains a refrigerant unless the person is certified under section 34". That certification is the Ozone Depletion Prevention (ODP) card, which you get after a one-day course; the card is valid for five years.
It works the other way too: the province's refrigerant certificate page says the ODP card alone does not let you work on refrigeration equipment as a mechanic. You need both.
09What happens if you fail?
STO's exam scheduling page says that if you do not pass, there is a mandatory 30-day waiting period before you can write the exam again, and you pay the exam fee again before you rebook. Results come within 15 business days of the exam.
Use the 30 days on the skill sets that cost you marks. A practice score by skill set shows where to start; on a paper weighted like the counselling sheet, Assemble and Install, Service and Maintain carry 63 per cent of the marks between them.
10Which codes and standards does the trade use?
Three standards come up across the 313D trade: CSA B52, the Mechanical Refrigeration Code; CSA F280, on sizing residential heating and cooling equipment from room-by-room loads; and the Ontario Electrical Safety Code for the branch circuit and disconnect. All three are CSA Group publications, and their text, tables and definitions may not be reproduced without permission. This page names them only, and our questions explain any requirement in their own words.
The law is different: Ontario's regulations are public on e-Laws and may be quoted, which is why the scope (O. Reg. 875/21) and the refrigerant rules (O. Reg. 463/10) are quoted here. STO's training standard and curriculum are copyright too, so we use them only for what they cover. Neither the current training standard nor the curriculum mentions A2L refrigerants, and STO does not say whether the exam tests them.
11How should you study for the 313D exam?
Follow the weights. Service, Maintain and Assemble and Install are 21 per cent each, electrical components 20 per cent, Commission 10 and Plan and Prepare 7. That puts 83 per cent of the marks on installing, servicing, maintaining and the electrical side, so most of your time belongs there.
- Practise reading readings. Superheat and subcooling, a temperature drop along a liquid line, amps on the run, start and common leads: much of service and commissioning is working out what a set of numbers means.
- Know the electrical side cold. A fifth of the sheet is electrical components: capacitors, contactors, transformers, thermostats, ECMs, sequences of operation and safe meter use.
- Know the limits of the trade. The s. 119 limits and what falls to 313A or to a gas technician are easy marks once you know them.
- Time a full paper. Work at least one 130-question set in four hours with nothing beside you, and check your score on each skill set as well as the total.
12How does TicketPrep's 313D practice exam work?
Our bank has 550 original questions, 400 Standard and 150 Advanced, across all six skill sets. Every question has four options and one correct answer, and explains all four. None is a recalled or shared exam question: STO's integrity policy treats capturing or sharing exam content as misconduct, and our bank is written from public sources only.
The timed mock exam is 130 questions in four hours, drawn 9, 27, 13, 28, 27 and 26 from skill sets A to F. Both the length and the split are ours, the sheet's percentages scaled to 130, because STO publishes no 313D question count. Each mock is scored against the 70 per cent pass mark and shows your score on each skill set.
You can try five questions free on the 313D practice exam page and read ten more on the free 313D questions page, with eight more on each skill-set page.
13Questions people ask
- How many questions are on the 313D exam?
- Skilled Trades Ontario does not publish a 313D question count. It says its certifying exams have between 90 and 150 multiple-choice questions and up to four hours. Our timed mock exam is 130 questions in four hours, a number we chose inside that range.
- What is the pass mark for the 313D exam?
- 70 per cent, according to STO's 313D exam counselling sheet and its Exam Prep Guide. No per-skill-set minimum is published.
- What are the 313D exam weights?
- STO's counselling sheet gives Plan and Prepare 7 per cent, Assemble and Install 21, Commission 10, Service 21, Maintain 21 and Service or Maintain Electrical Components 20. The sheet is dated 2016 and follows the older training standard, so the weights may not match today's exam.
- How much does the 313D exam cost?
- The exam fee is $150 + HST, paid in your STO Portal account. If you do not pass, you wait 30 days and pay the fee again before you rewrite. A Trade Equivalency Assessment, for experienced workers without an Ontario apprenticeship, is $235 + HST.
- Is the 313D exam open book?
- STO does not say. It states no formula sheet, and its integrity policy treats unauthorized paper, notes or calculations as misconduct, so prepare to write it with only what your exam confirmation allows.
- Is 313D a Red Seal trade?
- No. 313D is an Ontario-only compulsory trade with a provincial Certificate of Qualification exam. Its sister trade, 313A Refrigeration and Air Conditioning Systems Mechanic, is the Red Seal trade.
14Sources
- Skilled Trades Ontario: Residential Air Conditioning Systems Mechanic: the trade description, compulsory status, the 4,500-hour apprenticeship in two levels, and links to the training standard, curricula and counselling sheet. Accessed November 1, 2026.
- STO: 313D Exam Counselling Sheet (PDF): the 70 per cent pass mark and the six weighted skill sets; body dated December 5, 2016. Accessed November 1, 2026.
- STO: 313D Apprenticeship Training Standard, December 4, 2023 (PDF): the current skill sets and the general exam details: 90 to 150 multiple-choice questions, up to four hours, 70 per cent. Accessed November 1, 2026.
- STO: Exam Prep Guide, June 12, 2026 (PDF): exam format, paper based or electronic, results within 15 business days, what to bring and what is not permitted. Accessed November 1, 2026.
- STO: Exam scheduling: the $150 + HST exam fee and the 30-day wait before a rewrite. Accessed November 1, 2026.
- STO: Skilled Trades Ontario to deliver certifying exams in-house: STO delivery for exams on or after February 1, 2026. Accessed November 1, 2026.
- STO: Trade Equivalency Assessment: the route for experienced workers and its $235 + HST cost. Accessed November 1, 2026.
- O. Reg. 875/21, Scopes of Practice (e-Laws): s. 116 and s. 119, the 313A and 313D scopes. Accessed November 1, 2026.
- O. Reg. 463/10, Ozone Depleting Substances and Other Halocarbons (e-Laws): s. 22(1), certification to service or test refrigeration equipment. Accessed November 1, 2026.
- Ontario: Get a certificate to handle refrigerants: the ODP card, its one-day course and five-year term. Accessed November 1, 2026.
- STO: Fair Registration Practices Report 2025 (PDF): 313D certificate holders and new Certificates of Qualification. Accessed November 1, 2026.
The exam rules were read on Skilled Trades Ontario's pages and documents on November 1, 2026. Where STO does not state something, such as the 313D question count or whether the exam is open book, we say so instead of filling it in. The skill-set summaries are our own reading, and no STO, CSA or code text is reproduced on this page apart from the short quotations of Ontario regulations. STO is the final word on its exam; if you find something here out of date, tell us.
Related: 313D practice exam · Free 313D Residential AC practice questions · How to get your 313D licence in Ontario · 313A vs 313D: which licence you need · 313A Refrigeration and AC Red Seal exam guide · All guides
15Practice for this exam
TicketPrep 313D practice exams cover all six skill sets on STO's counselling sheet, every answer is explained, all four options, and every timed mock is 130 questions in four hours scored against the 70 per cent pass mark. You can try five sample questions with no account. The 313D Exam Pass is $69 one time for 120 days, and All-Access at $119 includes it along with 313A and every other exam on the site.
Ten free questions per trade, no account: free practice questions. How our questions are written and checked: how our questions are made.