Ontario has two compulsory trades that work on refrigerant systems, and the codes get mixed up constantly. The short version: 313A covers refrigeration and air conditioning systems broadly and is a Red Seal trade; 313D is limited to residential air conditioning and has a shorter apprenticeship. The details below come from Skilled Trades Ontario's trade pages.
How do 313A and 313D compare side by side?
| 313A | 313D | |
|---|---|---|
| Full name | Refrigeration and Air Conditioning Systems Mechanic | Residential Air Conditioning Systems Mechanic |
| Apprenticeship hours | 9,000 (8,280 on the job, 720 in school) | 4,500 (4,020 on the job, 480 in school) |
| Compulsory trade | Yes | Yes |
| Certifying exam | Yes: the interprovincial Red Seal exam, 125 questions | Yes: an Ontario certifying exam |
| Red Seal | Yes, as Refrigeration and Air Conditioning Mechanic | Not described as a Red Seal trade on its STO page |
Hours, compulsory status and exam requirements: Skilled Trades Ontario trade information pages, read 2026-09-21. Question count: the Red Seal examination weightings page.
What work does each trade cover?
The 313D description is built around residential air conditioning systems: planning, installing, starting up, servicing, repairing and commissioning them, and installing the piping that carries refrigerant for primary and secondary heating and cooling. 313A covers refrigeration and air conditioning systems without that residential limit, which is why its apprenticeship is twice as long and its exam follows the full Red Seal Major Work Activities.
If your work is mostly commercial refrigeration, walk-ins, rooftop units or anything outside a house, 313A is the trade that covers it. Check the exact scope of practice with Skilled Trades Ontario before you plan around it.
Is the 313A exam harder than the 313D exam?
They test different scopes, so "harder" depends on your background. The 313A exam draws from six work areas weighted by the Red Seal: maintenance and service is the largest at 25%, installation 21%, commissioning 17%, routine trade activities 16%, planning 13% and common occupational skills 8%. A residential mechanic moving to 313A usually has the most to learn in commercial refrigeration, controls and system planning. See how the 313A exam is weighted.
Which one should you study for?
The one on your training agreement or equivalency approval. If you are choosing a path, 313A carries the Red Seal and the broader scope; 313D is the shorter route into residential work. Examen Studio currently covers 313A only. Try five 313A questions to see where you stand.
Sources
- Skilled Trades Ontario: Refrigeration and Air Conditioning Systems Mechanic (313A)Hours, compulsory status, Red Seal title
- Skilled Trades Ontario: Residential Air Conditioning Systems Mechanic (313D)Hours, scope, compulsory status
- Red Seal: Refrigeration and Air Conditioning Mechanic examination weightings
Examen Studio is independent and not affiliated with the Red Seal Program or Skilled Trades Ontario. This article is a study aid; on the job, follow current codes, regulations and manufacturer instructions.