- OK-MECH is the trade exam for the HVACR Contractor Unlimited category under Oklahoma's mechanical licensing system.
- The Oklahoma Construction Industries Board sets requirements; PSI Services LLC administers the computer-based test.
- The trade exam has 90 questions in 240 minutes with a 70% passing score; PSI may add up to 10 unscored questions.
- Unlimited candidates must document experience on equipment above 25 tons and 500,000 Btu/h, not just residential-scale units.
What Is OK-MECH, Exactly?
"OK-MECH" on this site refers specifically to the Oklahoma Mechanical Trade License Exam - HVACR Contractor Unlimited track. It is the trade knowledge examination a candidate must pass to qualify for an Unlimited HVAC/R contractor license under Oklahoma's mechanical licensing structure. It is one piece of a larger licensing program administered by the Oklahoma Construction Industries Board (CIB), with the actual computer-based test delivered through PSI Services LLC.
This article focuses narrowly on the HVACR Contractor Unlimited trade portion - not the entire mechanical licensing program, and not the separate Business and Law examination that contractors must also pass. Understanding this distinction matters because Oklahoma's mechanical licensing covers multiple trade categories and specialty limits, and the questions, experience thresholds, and equipment-size requirements differ by category. If you want a full breakdown of what each domain covers, see the OK-MECH Exam Domains 2026 guide.
Who Takes This Exam and Why
The Unlimited designation is meaningful. Oklahoma's mechanical licensing includes limited and unlimited HVAC/R categories, and the Unlimited license is intended for contractors who work on larger commercial and industrial equipment. To sit for the HVACR Contractor Unlimited trade exam, applicants generally must:
- Be at least 18 years old.
- Meet the mechanical journeyman experience requirements, plus one additional year of qualifying experience.
- Be an owner, partner, officer, or permanent employee of a mechanical firm.
- Document qualifying work on equipment rated above 25 tons and 500,000 Btu/h - the threshold that separates Unlimited work from smaller-scale limited-category experience.
The standard experience-only path totals four years, though approved education can reduce the journeyman-experience component. Because these thresholds are specific and often misunderstood, candidates weighing whether they even qualify should review the full breakdown in OK-MECH Requirements 2026: Eligibility, Prerequisites & How to Qualify before spending time on exam prep.
In practical terms, this exam is aimed at working HVAC/R technicians and future contractors - people already installing, servicing, or supervising commercial-scale heating, cooling, and refrigeration systems who need the Unlimited license to bid larger jobs, pull permits as the licensed party, or advance into ownership or supervisory roles at a mechanical firm.
Exam Format and the Six Domains
The HVACR Contractor Unlimited trade exam is a computer-based test consisting of 90 questions delivered in 240 minutes, with a required passing score of 70%. PSI may embed up to 10 unscored experimental questions among the 90; time spent on those does not count against your working time, but you won't know which questions are experimental, so every item should be treated as scored.
Content is organized into six official subject areas with the following item allocations:
| Domain | Approx. Items |
|---|---|
| Electrical Knowledge and Controls | 15 |
| Natural Gas | 12 |
| Air Distribution Systems | 25 |
| Refrigeration and Air Conditioning Systems | 20 |
| Heating Systems | 15 |
| Safety | 3 |
Air Distribution Systems is the largest single domain at 25 of the 90 scored-and-unscored items combined - nearly a quarter of the entire exam. Refrigeration and Air Conditioning Systems is second-largest at 20 items. Together, those two domains account for close to half the test, which should directly shape how you allocate study time. For a domain-by-domain content breakdown, including subtopics within each area, see the complete domains guide.
Air Distribution Systems
As the highest-weighted domain, this area covers ductwork design principles, airflow calculations, static pressure concepts, and equipment sizing logic that Unlimited contractors are expected to apply on commercial-scale installations.
- Duct sizing and airflow balancing concepts
- Static pressure and system performance factors
- Use of ductulator-style calculation tools
Refrigeration and Air Conditioning Systems
The second-largest domain, testing knowledge of refrigeration cycles, system components, and AC-specific troubleshooting and installation practices relevant to unlimited-tonnage equipment.
- Refrigeration cycle fundamentals
- Component function and system troubleshooting logic
- Application to equipment above the 25-ton Unlimited threshold
If you're still forming a sense of how challenging this exam actually is relative to your current experience level, How Hard Is the OK-MECH Exam? Complete Difficulty Guide 2026 walks through that in more detail, and OK-MECH Passing Score 2026 explains exactly what the 70% threshold means in terms of correct answers needed.
Registration, Fees, and Eligibility Mechanics
Money and timing matter as much as content knowledge here. The trade examination fee is $92 per attempt, and the separate Business and Law portion also costs $92 per attempt - these are billed independently since they are separate exams. Beyond the exam fees themselves, the initial CIB application and license payment totals $330, made up of a $30 application fee and a $300 license fee.
Both required exams - the trade portion and Business and Law - must be passed within three years of eligibility approval under CIB rules. If you fail an attempt, retake timing is fixed: 30 days after a first failure, and 90 days after any subsequent failure. That waiting period makes it costly to walk in underprepared, since a failed attempt doesn't just cost $92 - it can push your licensing timeline back by a month or more.
Active contractor licensing also requires maintaining a $5,000 surety bond and $50,000 commercial general liability insurance, which are separate from the exam fees but necessary before the license becomes active. For a full line-item cost picture covering every fee in the process, see OK-MECH Certification Cost 2026: Complete Pricing Breakdown.
Key Takeaway
Budget for $92 per trade attempt, $92 for Business and Law, and $330 for the initial CIB application and license - and plan your study schedule around the 30/90-day retake waiting periods so a failed attempt doesn't stall your license timeline.
The current PSI bulletin governing this exam is effective August 31, 2026, and it's worth checking scheduling windows directly rather than assuming year-round availability. See OK-MECH Exam Dates 2026: Testing Windows, Deadlines & Scheduling for details on booking a seat.
Open-Book References and Allowed Materials
Unlike many trade exams, this one allows candidates to bring approved reference materials into the testing room - but the list is specific and it changes over time, so bringing the wrong edition can cause real problems on test day.
- Specified mechanical and fuel-gas codes
- A refrigeration textbook from the approved list
- An OSHA reference
- ACCA Manual N
- Mathematics for Plumbers and Pipefitters
- An ACCA ductulator
Edition timing matters: the 2024 IMC and IFGC become usable starting September 14, 2026, while the 2018 editions stop being allowed as of December 14, 2026 - meaning there's a window where either edition may work, and a firm cutoff after which only the newer code applies. Similarly, Modern Refrigeration and Air Conditioning, 22nd edition, became usable on August 13, 2026, while the 20th edition and the previously listed Refrigeration and Air Conditioning Technology, 5th edition, cease to be allowed on November 1, 2026.
You're allowed to bring books with pre-highlighting and permanent tabs, but handwritten notes are prohibited - so any prep involving marginalia needs to happen well before test day, in a study copy, not your test-day reference. A PSI-compliant non-programmable calculator is also permitted.
Building a Study Plan Around the Domain Weights
Generic study techniques only help if they're pointed at the right targets. Because Air Distribution Systems (25 items) and Refrigeration and Air Conditioning Systems (20 items) together make up nearly half the scored content, a study calendar that spends equal time on all six domains is a mistake. Safety, at only 3 items, still needs review - but it shouldn't consume a full study week when Air Distribution deserves multiple.
Air Distribution Systems & Refrigeration/AC
- Work through duct sizing, static pressure, and ductulator practice problems
- Review refrigeration cycle diagrams and component troubleshooting scenarios
Electrical Knowledge/Controls & Heating Systems
- Practice control circuit logic and wiring diagram interpretation
- Review heating system types, combustion basics, and venting concepts
Natural Gas, Safety & Full Review
- Cover fuel-gas code references and gas piping questions
- Run timed full-length practice covering all six domains together
Practicing under real time pressure matters because 240 minutes for 90 questions gives roughly 2.5 minutes per question on average - comfortable if you know the material, tight if you're still working through calculations by hand. Running full practice tests on our practice test platform before scheduling your official exam is one of the most direct ways to find out where your pacing breaks down. A structured week-by-week plan with more detail is available in the OK-MECH Study Guide 2026.
After You Pass: Licensing and Renewal
Passing the trade exam and the Business and Law exam is the gateway, not the finish line. Once licensed, contractors renew annually in their birth month, paying a $200 contractor renewal fee. Continuing education requires six approved hours every 36 months, though there's an initial three-year examination exemption after first licensing.
This ongoing structure is worth factoring into any decision about whether pursuing the Unlimited license makes sense for your career stage - the $92 exam fee and $330 initial license payment are just the entry cost; renewal and CE are recurring. If you're weighing the long-term value against the cost and effort, Is the OK-MECH Certification Worth It? Complete ROI Analysis 2026 covers that tradeoff, and OK-MECH Salary Guide 2026 looks at earnings-side considerations for licensed contractors.
For candidates who want a quick-reference summary of every number in this article - fees, timing, domain weights, and reference editions - the OK-MECH Cheat Sheet 2026 condenses it to one page, and running a few timed sets on the practice test site is a fast way to confirm readiness before you commit to a scheduled seat.
Frequently Asked Questions
OK-MECH is this site's identifier for the Oklahoma Mechanical Trade License Exam - HVACR Contractor Unlimited. It is not a separately branded credential; it's the trade exam within Oklahoma's CIB-administered mechanical licensing program.
The HVACR Contractor Unlimited trade exam has 90 questions to answer in 240 minutes, with a required score of 70% to pass. Up to 10 additional unscored experimental questions may appear without extra time penalty.
Air Distribution Systems, with 25 of the 90 items, is the single largest domain. Refrigeration and Air Conditioning Systems follows at 20 items. Together they represent nearly half the exam's content.
You must wait 30 days before retaking after a first failure, and 90 days after any subsequent failure. Both the trade exam and the Business and Law exam must be passed within three years of eligibility approval.
No. Handwritten notes are prohibited. You may use approved reference books with pre-highlighting and permanent tabs, plus a PSI-compliant non-programmable calculator, but nothing handwritten is allowed at the testing station.