Blog
The readings, rules and reasoning behind 313A questions
Explanations of concepts that come up again and again, each tied to the work areas it belongs to and linked to its sources.
- October 16, 2026 · Area B + F
Oil pressure safety control: what pressure is it checking?
Read an oil safety control as a differential measurement: pump outlet pressure minus crankcase pressure, with a model-specific time delay.
- October 13, 2026 · All areas
Does US HVAC experience qualify you to challenge Ontario 313A?
How a US-trained mechanic can check the 313A Trade Equivalency Assessment route, document work across the trade and avoid assuming a US credential grants exam access.
- October 13, 2026 · Area B + D + F
Suction burnout drier vs liquid-line drier: which job is each doing?
Read the flow path after compressor burnout and distinguish a suction-line cleanup drier from a routine liquid-line filter drier without assuming one replaces the other.
- October 12, 2026 · All areas
Is your first Ontario 313A exam attempt free?
STO's completed-apprentice first-attempt waiver, the January 2025 cutoff, and why a trade qualifier should check the fee shown in their own portal.
- October 12, 2026 · Area B + E + F
Start capacitor, run capacitor, or potential relay: which stays in circuit?
Read a single-phase compressor start circuit: what the potential relay removes after starting and when a run capacitor remains connected.
- October 10, 2026 · All areas
How should you study 313A equipment you rarely work on?
A practical way to review unfamiliar refrigeration and HVAC equipment for the Ontario 313A without relying on rumours about the exam mix.
- October 10, 2026 · Area B + E + F
Sight glass bubbles or a yellow indicator: what is the difference?
Separate visible vapour in a liquid-line sight glass from its moisture indicator, and learn why neither observation alone proves a refrigerant charge fault.
- October 9, 2026 · All areas
Can you use a dictionary on the Ontario 313A exam?
STO's current language and dictionary rules for booked 313A candidates, including how to request approval for a word-to-word foreign-language dictionary.
- October 9, 2026 · Area B + F
Why does a compressor short-cycle despite a time delay?
Separate a short compressor run from a protective restart delay, then trace the control sequence without assuming one universal timer setting.
- October 8, 2026 · All areas
Do you need your rsexam.ca password on Ontario 313A exam day?
STO's current scheduling page and an older candidate PDF give different exam-day password instructions. Here is how to resolve the conflict before your sitting.
- October 8, 2026 · Area D + F
TXV equalizer line or sensing bulb: what does each sense?
Trace temperature and pressure inputs to a TXV, then explain why an external equalizer matters across an evaporator pressure drop.
- October 7, 2026 · All areas
How should a 313A candidate use the Red Seal self-assessment?
Use the current-exam refrigeration self-assessment to find unfamiliar tasks, without treating its result as an exam score or pass prediction.
- October 7, 2026 · Area E + F
What stops the compressor in an automatic pump-down cycle?
Follow the thermostat, liquid-line solenoid and low-pressure control through a refrigeration pump-down and restart.
- October 6, 2026 · All areas
Are Red Seal 313A sample questions like the actual exam?
What the official refrigeration sample questions show, what they cannot predict, and how to review each answer before a booked 313A sitting.
- October 6, 2026 · Area A + F
Compressor megohmmeter or ohmmeter: what does each test tell you?
Separate winding continuity from insulation leakage to ground, and understand why one compressor reading should not become a universal pass threshold.
- October 5, 2026 · All areas
Which formulas are supplied on the 313A Red Seal exam?
Find the official refrigeration formula list and practise choosing and using a formula instead of memorizing a page blindly.
- October 5, 2026 · Area B + E + F
Crankcase heater or suction fix: when does liquid reach a compressor?
Distinguish off-cycle refrigerant migration from liquid floodback while the compressor runs, using the timing of the symptom.
- October 4, 2026 · All areas
Where do you find Ontario 313A exam results?
Find your certifying exam result through Skilled Trades Ontario and turn it into a focused next study step.
- October 4, 2026 · Area B + D + F
When does a heat pump need a bi-flow filter drier?
A simple flow-direction exercise for distinguishing a one-way liquid-line drier from a bi-flow design.
- October 3, 2026 · All areas
Need to reschedule a booked Ontario 313A exam?
What to check in your booking confirmation and rsexam.ca profile, and how to get rescheduling help from Skilled Trades Ontario.
- October 3, 2026 · Area B + F
Why can an open fuse show voltage across it?
Use a simple HVAC control-circuit sketch to distinguish voltage across an open point from voltage drop across a loaded closed contact.
- October 2, 2026 · All areas
Can you use AI to study for the 313A Red Seal exam?
A practical way to check AI-generated 313A explanations and practice questions against the current exam standard and reliable trade sources.
- October 2, 2026 · Area D + F
Where should a TXV sensing bulb go, and why?
Trace what a thermostatic expansion valve bulb senses, why pipe position matters, and how an external equalizer differs.
- October 1, 2026 · All areas
Is a paid 313A pre-exam course worth it?
A decision checklist for Ontario 313A candidates comparing a paid prep course with official free resources and their own study gaps.
- October 1, 2026 · Area B + F
Motor overload relay vs contactor: which one stops the motor?
Trace an overload trip through the motor starter control circuit without confusing overload protection with short-circuit protection.
- September 30, 2026 · All areas
What should you bring to your Ontario 313A exam?
A booked 313A candidate's exam-day check: confirmation, government photo ID, restricted belongings and who to ask about the room's instructions.
- September 30, 2026 · Area B + E + F
Defrost termination vs fan delay: why do the fans wait?
Follow a unit cooler's defrost thermostat from warm-coil termination to cold-coil fan restart, using a Heatcraft manual as a model-specific example.
- September 29, 2026 · All areas
Where will you write the 313A exam under STO's in-house delivery?
How a booked Ontario 313A candidate can confirm the actual exam site, time and delivery details after Skilled Trades Ontario brought exams in-house.
- September 29, 2026 · Area B + E + F
High-pressure cutout or condenser-fan control: which switch opens?
Read open-high and open-low pressure-switch action using a simple rising-pressure example, without confusing fan cycling with a safety cutout.
- September 28, 2026 · All areas
Finished your 313A apprenticeship? Check your provisional certificate
What Ontario's provisional Certificate of Qualification means while a completed 313A apprentice prepares for the certifying exam, and what to verify before booking.
- September 28, 2026 · Area B + E + F
How do you calculate three-phase voltage unbalance?
Work a three-line-voltage example: find the average, largest deviation and percent unbalance, then explain what the number can and cannot diagnose.
- September 27, 2026 · All areas
Failed the 313A exam? What to check before a rewrite
Ontario's 30-day rewrite wait, repeat exam fee and booking checks, plus a practical way to choose what to study for your next 313A attempt.
- September 27, 2026 · Area B + E + F
Why volts × amps is not always motor watts
A worked single-phase motor calculation for 313A study: distinguish volt-amperes, watts, power factor and efficiency before choosing a formula.
- September 26, 2026 · All areas
Need 313A exam accommodations? Ask before booking
How to request Ontario certifying-exam accommodations, what the STO form asks for, and what to confirm before choosing your 313A exam date.
- September 26, 2026 · Area A + E + F
Why can parallel paths lower an ohmmeter reading?
A 313A study example showing why in-circuit resistance can be lower than a component's value, with parallel-path arithmetic and a check on the conclusion.
- September 25, 2026 · All areas
Booked the Ontario 313A? Set up your rsexam.ca account
When Ontario's Red Seal exam activation email arrives, what to check, how long the temporary password lasts, and what to do if your session details are wrong.
- September 25, 2026 · Area C + E + F
How do you use the 1.08 × CFM × ΔT formula?
A worked 313A study example for sensible heat, airflow and temperature difference, including units and the limits of a dry-bulb calculation.
- September 24, 2026 · All areas
Which Red Seal standard should a 313A candidate study?
The Red Seal site shows a newer refrigeration standard and a separate standard for current exams. Here is how to tell them apart before planning 313A study time.
- September 24, 2026 · Area E + F
Low-pressure control cut-in and cut-out: which happens first?
A worked 313A study example for reading a low-pressure control's cut-in, cut-out and differential without confusing an operating control with a safety lockout.
- September 22, 2026 · All areas
313A vs 313D: which Ontario refrigeration trade is which?
The difference between the 313A Refrigeration and Air Conditioning Systems Mechanic and the 313D Residential Air Conditioning Systems Mechanic: scope, hours, exams and Red Seal status.
- September 22, 2026 · All areas
Challenging the 313A exam: the Trade Equivalency Assessment explained
Experienced but never apprenticed in Ontario? How the Trade Equivalency Assessment decides whether you can challenge the 313A certificate of qualification exam, what it costs, and what evidence counts.
- September 21, 2026 · Area E + F
Superheat vs subcooling: what each reading tells you
Superheat reads the evaporator, subcooling reads the condenser. How to calculate both, which one to charge by, and how to read them together.
- September 21, 2026 · Area F
Undercharge or restriction? Telling two starved evaporators apart
Low suction pressure and high superheat can mean a leak or a restriction. Subcooling and a temperature drop across the drier tell you which.
- September 21, 2026 · Area B
Reading a vacuum decay test: leak or moisture?
What a micron gauge is telling you after you valve off the pump, why the compound gauge can't, and how to set up an evacuation that finishes.
- September 21, 2026 · Area B + E
Temperature glide, dew point and bubble point, explained
Why zeotropic blends like R-407C have two PT values, which one to use for superheat and subcooling, and why they must be charged as liquid.
- September 21, 2026 · Area B
What Canada's Federal Halocarbon Regulations, 2022 actually say
A section-by-section summary of the rules on release, recovery, leak testing and charging, who they apply to, and where Ontario's own regulation takes over.
- September 21, 2026 · Area A + D
A2L refrigerants: what the safety class means for the job
What the A and the 2L stand for, which common refrigerants are A2L, and what changes in tools, recovery and installation practice.
- September 21, 2026 · Area F
Identifying compressor terminals with an ohmmeter
How to find common, start and run on a single-phase compressor from three resistance readings, check the math, and test for a grounded winding.
- September 21, 2026 · All areas
How to build a 90-day 313A study plan
How to verify the Red Seal breakdown for your exam, find weak areas early, and use the last weeks for review instead of new material.