- The OH-REF trade exam has 60 scored questions across 5 domains, plus 10 unscored pretest items.
- Domain 1 (General Knowledge & Requirements) carries the most weight at 18 of 60 scored questions.
- Domain 4 (Refrigeration Systems & Controls) is second-heaviest at 15 of 60 scored questions.
- The exam is open-book, computer-based, and limited to a 3-hour session with a 70% passing score.
Exam Format Overview
Before breaking down each content area, it helps to understand how PSI structures the Ohio Refrigeration Contractor License Exam. The trade exam administers 70 total questions, but only 60 are scored - the remaining 10 are unscored pretest items PSI uses to evaluate future exam content. Candidates get 3 hours to complete the exam and must score 70% or higher on the scored portion to pass. The test is computer-based, delivered at PSI test centers, and it is open-book, meaning approved references can be brought to the testing station.
Understanding the exact domain breakdown matters because it tells you where to spend your limited study hours. If you're still deciding how much prep time you need overall, pairing this domain breakdown with the OH-REF Study Guide and a look at how hard the OH-REF exam actually is will give you a fuller picture before you schedule test day.
Domain 1: General Knowledge & Requirements (18 of 60 scored questions)
General Knowledge & Requirements is the largest domain on the OH-REF trade exam, and it's also the domain most tied to Ohio-specific regulatory content rather than pure trade skill. This is where the exam checks whether you understand the rules governing how refrigeration contracting is legally practiced in Ohio, not just how a compressor works.
Domain 1: General Knowledge & Requirements
Candidates must understand the regulatory and code framework surrounding refrigeration contracting in Ohio.
- Provisions of the 2024 Ohio Mechanical Code that apply to refrigeration installations
- Scope of work distinctions - refrigeration for food and product preservation versus comfort-cooling HVAC
- Permitting, licensing, and jurisdictional basics governed by OCILB
- General safety practices and code-referenced terminology used throughout the exam
Because Domain 1 touches nearly a third of the scored exam, candidates who under-prepare here often find their overall score drags even if they're strong on hands-on refrigeration mechanics. This is a domain where reading comprehension and code-navigation speed matter as much as memorized facts.
Domain 2: Refrigeration Piping (12 of 60 scored questions)
Refrigeration Piping covers the physical installation side of the trade - how refrigerant lines are sized, routed, supported, and protected across a system. Expect scenario-based questions that describe a piping situation and ask you to identify the correct code-compliant response.
Domain 2: Refrigeration Piping
Candidates must apply piping principles specific to refrigeration systems rather than general plumbing.
- Line sizing considerations for suction, discharge, and liquid lines
- Pipe support, insulation, and protection requirements
- Joining methods and materials appropriate for refrigeration piping
- Identifying installation errors in described or illustrated piping layouts
This domain rewards candidates who have real field time running refrigeration piping - book knowledge alone tends to fall short here because questions often describe a physical installation scenario rather than asking for a definition.
Domain 3: Refrigerants (6 of 60 scored questions)
Refrigerants is the smallest domain by question count, but that doesn't mean it's skippable. With only 6 scored questions, every missed question here has outsized impact on your percentage within the topic - though it has less overall weight on your total score than the larger domains.
Domain 3: Refrigerants
Candidates must know how refrigerants behave and how they're handled safely and legally.
- Basic refrigerant properties and behavior within a refrigeration cycle
- Handling, recovery, and containment practices
- Safety hazards associated with common refrigerants used in preservation systems
- Recognizing refrigerant-related terminology referenced in your approved code references
Because this domain is compact, it's an efficient place to build quick confidence early in your prep - a focused review session can cover the bulk of what's testable in a short amount of time.
Domain 4: Refrigeration Systems & Controls (15 of 60 scored questions)
Refrigeration Systems & Controls is the second-largest domain and the technical heart of the exam. This is where the test evaluates whether you actually understand how a refrigeration system functions as a whole - compressors, evaporators, condensers, and the controls that keep them operating safely for food and product preservation.
Domain 4: Refrigeration Systems & Controls
Candidates must understand system components, cycle behavior, and control logic.
- Compression cycle fundamentals as applied to preservation refrigeration (not comfort cooling)
- Component function: compressors, condensers, evaporators, metering devices
- Control devices - thermostats, pressure controls, defrost controls, and safety cutouts
- Troubleshooting logic when a described system behaves outside normal parameters
Combined, Domains 1 and 4 account for 33 of the 60 scored questions - more than half the exam. If you only have time to master two domains deeply, these are the two that carry the most weight toward your final score.
Domain 5: Testing & Inspection (9 of 60 scored questions)
Testing & Inspection covers the verification side of the trade: how a refrigeration installation is checked, tested, and signed off before it's considered complete and code-compliant.
Domain 5: Testing & Inspection
Candidates must know how to verify system performance and compliance after installation.
- Pressure and leak testing procedures for refrigeration piping and components
- Startup and commissioning checks for a completed refrigeration system
- Documentation and inspection sign-off expectations under Ohio code
- Identifying test results that indicate a failed or non-compliant installation
Domain Weight Comparison
Here's how the five domains stack up by scored question count on the OH-REF trade exam:
| Domain | Scored Questions | Share of 60 |
|---|---|---|
| Domain 1: General Knowledge & Requirements | 18 | Largest domain |
| Domain 2: Refrigeration Piping | 12 | Third largest |
| Domain 3: Refrigerants | 6 | Smallest domain |
| Domain 4: Refrigeration Systems & Controls | 15 | Second largest |
| Domain 5: Testing & Inspection | 9 | Fourth largest |
For a deeper breakdown of what "70%" actually means against these weightings, see the OH-REF Passing Score guide, which walks through how the scored total translates into a pass or fail result.
Key Takeaway
Because Domains 1 and 4 together make up 33 of 60 scored questions, prioritize General Knowledge & Requirements and Refrigeration Systems & Controls first, then layer in Piping, Testing & Inspection, and Refrigerants.
The Business and Law Companion Exam
The trade exam covered above is only half of the licensing requirement. Ohio also requires a separate Business and Law examination, administered by PSI as its own test with its own fee. It contains 50 scored questions plus 5 pretest questions, runs on a 2-hour limit, and also requires a 70% passing score. Unlike the trade exam's five technical domains, Business and Law focuses on contract law, licensing regulations, insurance obligations, and general business practices required of Ohio contractors.
Each exam - trade and Business and Law - is charged separately at $69 per attempt through PSI. If you fail either portion, Ohio requires a 60-day wait before you can retest that section, and PSI allows up to five retests within a year. Budgeting for both exams, plus potential retests, is worth planning ahead of time; the OH-REF Certification Cost breakdown lays out every fee from application through renewal.
Mapping a Study Timeline to the Domains
Rather than studying domains in the order they're listed, it makes more sense to sequence your prep by question weight and personal familiarity. A candidate with strong field experience in piping and systems work but limited exposure to Ohio-specific code language, for example, should front-load Domain 1.
Domain 1 & Domain 4 Foundation
- Work through the 2024 Ohio Mechanical Code sections relevant to refrigeration
- Review compressor, evaporator, condenser, and control device function
Domain 2 Piping Practice
- Study line sizing and support requirements using Modern Refrigeration and Air Conditioning, 22nd edition
- Practice scenario questions describing piping installations
Domain 5 and Domain 3 Review
- Cover testing, leak-checking, and commissioning procedures
- Finish with refrigerant handling and safety basics
Full Practice and Reference Indexing
- Take full-length timed practice sessions under the 3-hour limit
- Finalize tabbing and indexing in your approved open-book references
This kind of sequencing is a light structural overlay - it's not meant to replace deep review of the actual code material. If you want a condensed version of the highest-yield facts to revisit the night before your test, the OH-REF Cheat Sheet is built around exactly that kind of last-pass review.
Who This Domain Structure Actually Serves
It's worth remembering that these five domains exist to validate a very specific scope of work: refrigeration contracting for food and product preservation, not comfort-cooling HVAC. That distinction shapes every domain - the piping, controls, and testing questions are all framed around preservation refrigeration systems used by grocery, food service, cold storage, and commercial refrigeration employers across Ohio. If you're weighing whether this license is worth pursuing relative to other paths, the ROI analysis and salary guide both go deeper into how licensed contractors in this scope position themselves in the market, while OH-REF Jobs covers where licensed contractors typically find work.
Before you commit to a study plan built around these domains, double-check that you actually meet the eligibility path required to sit for the exam in the first place - Ohio's standard route requires five years of documented trade experience, and there are alternative paths for engineers and government trade inspectors. The full breakdown lives in OH-REF Requirements.
Once you've worked through each domain individually, it's worth checking your overall readiness against real performance data rather than gut feeling. The OH-REF Pass Rate article and the domain-by-domain practice questions on the main practice test site are good ways to stress-test your prep before you pay for an actual attempt.
FAQ
There are five domains: General Knowledge & Requirements, Refrigeration Piping, Refrigerants, Refrigeration Systems & Controls, and Testing & Inspection, totaling 60 scored questions.
General Knowledge & Requirements is the largest domain with 18 of 60 scored questions, followed by Refrigeration Systems & Controls with 15.
No. Business and Law is a separate exam with 50 scored questions and a 2-hour limit, required in addition to the trade exam's five domains.
You can bring approved references with advance highlighting, underlining, and indexing, but handwritten notes and additional loose papers are not permitted.
Since the exam is scored as a whole rather than domain-by-domain pass/fail, a failed attempt requires a 60-day wait before retesting, with up to five retests allowed per year.