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Oklahoma HVACR Contractor Unlimited — Practice Exam Guide

What This Practice Exam Covers

The Oklahoma HVACR Contractor Unlimited licensing exam consists of 90 questions delivered over 240 minutes, with a passing score of 70% (63 correct answers). The exam spans six topic areas drawn from electrical systems, natural gas, air distribution, refrigeration, heating, and safety.

Two practice options are available here:

Free practice exam: 10 questions per attempt, pulled from a limited question pool. You can retake it as many times as you like — it costs nothing and gives you a quick feel for the question style, phrasing, and difficulty level before you commit to deeper preparation.

Full practice exam (paid): 90 questions with a 240-minute time limit, mirroring the real exam exactly. Questions are drawn from a pool of 282+ items, so every attempt produces a unique exam — you won't see the same set twice. All questions are based on the official topic breakdown provided by the exam authority.

What You'll Be Tested On

Air Distribution Systems — 25 items (28% of exam)

This is the heaviest topic and deserves the most study time. Expect calculation-based questions on mixed-air temperature (as shown in the sample below), duct sizing per ACCA Manual D, and ventilation rates including air changes per hour. You must know duct system configurations — radial, extended plenum, reducing trunk, perimeter loop, and small-duct high-velocity (SDHV) — and when each is appropriate. The 2021 IMC governs most of this content: duct construction materials and gauges fall under IMC 2021, Section 603.2; joining and sealing methods under Sections 603.4.2 and 603.9; insulation requirements and vapor retarders under Sections 604.2 and 604.7. Registers, diffusers, grilles, and damper types are tested on function and placement, not just definition. IMC 2021, Section 401.2 covers outdoor air requirements, while Section 403.3.2.1 Exception addresses demand-controlled ventilation. Flame-spread and smoke-developed ratings for duct materials appear regularly.

Refrigeration and Air Conditioning Systems — 20 items (22%)

Questions cover the full vapor-compression cycle and all four major components. Metering device questions — fixed orifice vs. TXV vs. electronic expansion valve — focus on selection criteria and operating behavior. Compressor types (reciprocating, scroll, screw, centrifugal) and their safety components are drawn from Modern Refrigeration and Air Conditioning, Chapter 18. Refrigerant classification under the EPA 608 framework is heavily tested: recovery requirements by refrigerant class, evacuation levels (see sample question below), and the distinction between low-pressure, medium-pressure, and high-pressure refrigerants. Leak detection methods, charging procedures, and proper cylinder handling all appear. Condenser and evaporator types, along with defrost methods for low-temperature applications, round out this section.

Electrical Knowledge and Controls — 15 items (17%)

Every candidate must be comfortable with Ohm's Law and Watt's Law calculations in series, parallel, and series-parallel circuits. Control system questions test range and differential adjustment and the ability to calculate cut-in and cut-out set points from given values. Motor starting relays are a reliable test target: know the operating principle of current relays, potential relays, solid-state relays, and PTC (positive temperature coefficient) relays — covered in Chapter 16, Sections 16.3.5. Pressure motor controls (high-pressure, low-pressure, oil pressure) appear in Chapter 16, Section 16.3.4. NEC Article 725 governs low-voltage control circuit wiring (see sample question). Ladder diagrams and pictorial wiring diagrams are tested on reading and interpretation, not drafting.

Heating Systems — 15 items (17%)

Gas-fired systems cover burner types, combination gas valves, ignition systems (standing pilot, intermittent, direct spark), and heat exchanger inspection. Oil-fired heating questions include combustion efficiency testing: CO₂ percentage, stack temperature measurement, draft testing, and smoke spot number — drawn from Modern Refrigeration and Air Conditioning, Oil-Fired Heating Systems. Hydronic heating questions address boiler components, circulator pumps, expansion tank sizing, and piping configurations (series loop, one-pipe, two-pipe, radiant). Electric resistance heating covers duct heaters, baseboard units, and sequencer operation. Load calculation questions use R-values, U-values, and the Manual J method — know the difference between R (resistance) and U (conductance) and how to apply design temperature differences.

Natural Gas — 12 items (13%)

Gas piping sizing uses three methods: longest length, branch length, and hybrid pressure — with questions drawn from IFGC 2018, Page 32 (Table 402.4) and Appendix A. Allowable pressure drop and maximum operating pressure limits are tested directly. Combustion air sizing calculations require knowing the indoor, outdoor, and combination methods. Venting questions cover appliance categories (Category I–IV), vent types (Type B, Type BW, Type L), and termination clearances under IFGC 2018, Sections 305.3 and 305.5. Pipe materials — steel, copper, CSST, polyethylene — and their allowable applications appear in Section 401.4 and 401.5.

Safety — 3 items (3%)

Three questions, but missing one still hurts your score. Expect one question on LOTO procedures, one on SDS/GHS labeling (the nine pictogram system under HVACR Textbook, Chapter 2, Section 2.2.6), and one on fire extinguisher operation (P.A.S.S.) or refrigerant cylinder pressure safety (Chapter 2, Section 2.2.4). PPE selection and respiratory protection requirements also appear.

Worked Sample Questions

Sample 1 — Air Distribution Systems

A rooftop unit mixes 2,000 CFM at 65°F with 1,000 CFM at 90°F. What is the mixed air temperature?

• A. 70°F
• B. 73°F
• C. 75°F
• D. 80°F

Correct Answer: B — 73°F

Use the mass-weighted average formula: multiply each airstream's CFM by its temperature, sum the results, then divide by total CFM.

[(2,000 × 65) + (1,000 × 90)] ÷ 3,000
= [130,000 + 90,000] ÷ 3,000
= 220,000 ÷ 3,000
= 73.3°F → 73°F

The larger airstream dominates the result. Candidates who average the two temperatures (65 + 90 ÷ 2 = 77.5°F) ignore airflow weighting and select a wrong answer. Always weight by CFM.

Sample 2 — Refrigeration and Air Conditioning Systems

What evacuation level is required for low-pressure refrigerants (R-123)?

• A. 10" Hg
• B. 15" Hg
• C. 20" Hg
• D. 25 mm Hg absolute

Correct Answer: D — 25 mm Hg absolute

EPA Section 608 establishes recovery and evacuation requirements by refrigerant pressure class. Low-pressure refrigerants (such as R-123, used in centrifugal chillers) must be evacuated to 25 mm Hg absolute — a much deeper vacuum than medium- or high-pressure refrigerants require. Note that the unit is mm Hg absolute, not inches Hg vacuum. Confusing the unit or the pressure class is a common error on this question type.

Sample 3 — Electrical Knowledge and Controls

A heat pump has a reversing valve rated at 24V control voltage. What NEC Article governs control circuit wiring?

• A. 430
• B. 440
• C. 725
• D. 760

Correct Answer: C — NEC Article 725

NEC Article 430 covers motors generally; Article 440 covers hermetic refrigerant motor-compressors. Article 760 governs fire alarm circuits. Article 725 covers Class 1, Class 2, and Class 3 remote-control, signaling, and power-limited circuits — which includes the 24V low-voltage control wiring found throughout HVACR systems. Any time a question involves thermostat wire, control transformer output, or low-voltage relay coils, Article 725 is the governing reference. This is cited in Chapter 16, Section 16.4.1 of the study materials.

How to Read Your Score

The passing threshold is 70%, meaning you need at least 63 of 90 questions correct on the real exam.

On your first practice attempt, treat your score as a diagnostic — a map of where you stand, not a prediction of what will happen on exam day. A score in the 50s tells you which topic areas need focused work. A score in the 60s means you're in the right range but not yet safe; scoring 68–69% on practice typically indicates you need more repetition before the real exam, because practice familiarity can inflate results slightly.

The full practice exam provides a topic-by-topic breakdown after each attempt. Use it. If you scored 85% on Electrical but 55% on Air Distribution Systems (the largest topic at 25 items), your study time should reflect that imbalance — not split equally across all six areas. Run multiple attempts over several days, watching for consistent weak spots versus questions you missed once due to rushing. Consistent misses in one subtopic — say, duct sizing calculations or gas piping table lookups — tell you exactly what to review before sitting for your license.

Where Candidates Lose Points

Air Distribution Systems is where most exams are won or lost. At 25 items, a weak performance here can knock you below passing even if you ace everything else. The most common errors are unit confusion in ventilation calculations (CFM vs. ACH) and failing to apply ACCA Manual D correctly to duct sizing problems.

Multi-step calculations across all topics — mixed-air temperature, combustion air sizing, circuit calculations — reward candidates who write out every step. Skipping steps causes unit errors and arithmetic mistakes under time pressure.

Code table lookups in Natural Gas trip up candidates who memorize concepts but haven't practiced using IFGC Table 402.4 or Appendix A sizing tables. The exam expects you to read a table accurately, not recall a number from memory.

Motor relay identification in Electrical is a point-loss trap. Current relays, potential relays, PTC relays, and solid-state relays have distinct operating principles. Mixing up when a relay opens or closes relative to motor start loses easy points.

Refrigerant pressure class errors — applying medium-pressure evacuation standards to a low-pressure refrigerant, or misidentifying a refrigerant's safety group — cost points in Refrigeration.

Time management: 240 minutes for 90 questions averages 2 minutes 40 seconds per question. Calculation-heavy sections like Air Distribution and Heating can consume disproportionate time if you're not careful.

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