10 exam-style questions with answers and explanations, straight from our 1,030-question bank. Tap an answer to check yourself. When you're ready, take the scored version in the free practice test.
The OH-REF exam has 70 questions and runs 3 hours.
These 10 free OH-REF questions are organized by exam domain, so you can see how each part of the Ohio Refrigeration Contractor License Exam blueprint is tested. Reveal the answer and explanation under each question.
Domain 1: General Knowledge & Requirements
Question 1
Frost is visible on an exposed suction-line section at a walk-in cooler's evaporator outlet. A clamped, insulated probe beside the TXV bulb reads 28°F. At that location, the zeotropic refrigerant's chart gives a 10°F bubble point and a 20°F dew point. Pressure measured farther downstream at the compressor corresponds to a 14°F dew point. With normal airflow, steady load, and a specified evaporator superheat range of 6-10°F, what do these measurements support?
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Correct answer: D - 8°F superheat; retain the present TXV adjustment.
Question 2
An ice plant converts 160 lb of water at 68°F into ice at 14°F over 4 hours. Use specific heats of 1.0 Btu/(lb·°F) for water and 0.5 Btu/(lb·°F) for ice, with 144 Btu/lb removed during freezing at 32°F. Compressor work adds an average of 4,000 Btu/h to the refrigerant. Neglect all other heat gains. What average heat-rejection rate must the condenser handle during this batch?
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Correct answer: B - 11,560 Btu/h
Question 3
An electrical submittal for a refrigeration condensing unit lists MCA 28 A and MOCP 45 A. The proposed conductor ampacities already include all required corrections and adjustments, and the installation instructions permit the proposed breaker type. Considering these two nameplate limits, which combination is acceptable?
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Correct answer: D - Conductors with 35 A allowable ampacity and a 40 A breaker.
Domain 2: Refrigeration Piping
Question 4
A parallel-compressor rack returns oil reliably at full load but leaves oil in its vertical suction riser when compressors unload. The existing riser is too large to maintain oil-return velocity at minimum load. Calculations also show that a smaller single riser would exceed the allowable full-load pressure drop. Which piping revision accommodates both operating conditions?
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Correct answer: B - Use a double riser with a properly sized low-load leg.
Question 5
Soon after a new copper liquid line is commissioned, black flakes plug the TXV inlet strainer. A removed brazed joint has matching black scale on its inner surface. The tubing was clean before assembly. Which omitted fabrication practice would most directly have prevented this contamination?
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Correct answer: A - Sweeping dry nitrogen through the tubing, with an open outlet, during brazing.
Domain 3: Refrigerants
Question 6
An approved R-448A charging procedure calls for completing a weighed charge through the suction service connection while the compressor runs. The supply cylinder has separate vapor and liquid withdrawal connections. Which transfer method preserves the blend composition without sending a liquid slug to the compressor?
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Correct answer: D - Withdraw liquid and meter the flow so only vapor reaches the compressor.
Domain 4: Refrigeration Systems & Controls
Question 7
A store manager reports, 'The compressor keeps running after the walk-in reaches temperature.' The thermostat controls a normally closed liquid-line solenoid, and a low-pressure control operates the compressor contactor. When the thermostat is satisfied, the solenoid closes, suction pressure falls, and the compressor stops at its specified low-pressure cutout. How should the contractor assess this sequence?
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Correct answer: C - Normal automatic pumpdown; no control change is indicated.
Question 8
A walk-in freezer blows a burst of warm, moisture-laden air across stored cartons when cooling resumes after electric defrost. Heater termination and the drip period match the service instructions. The fans start with the compressor while the coil is still warm. Which control change addresses this discharge?
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Correct answer: C - Restore fan delay so airflow waits until the coil has cooled.
Question 9
A distributor-fed evaporator was fitted with an internally equalized TXV. Subcooled liquid reaches the valve, and the sensing bulb is properly secured at the evaporator outlet, but the coil starves as distributor pressure drop increases with load. The long suction line to the compressor adds further pressure loss. Which specification belongs on the replacement order?
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Correct answer: C - Externally equalized TXV; take equalizer pressure at the evaporator outlet.
Domain 5: Testing & Inspection
Question 10
Service readings from a warm walk-in cooler show 24°F evaporator-outlet superheat against an 8-12°F specification during steady operation. Evaporator airflow is normal. Liquid entering the filter-drier has 12°F subcooling. Pressure taps show a 14 psi drop across the drier, versus a permitted maximum of 2 psi at this flow, and the downstream sight glass bubbles. Which fault best accounts for the combined findings?
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Correct answer: A - A restriction in the liquid-line filter-drier.
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