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 CRST exam has 150 questions and runs 3 hours.
These 10 free CRST questions are organized by exam domain, so you can see how each part of the Certified Refrigeration Service Technician blueprint is tested. Reveal the answer and explanation under each question.
While approaching an ammonia machinery room, a service technician's functioning monitor indicates 420 ppm ammonia and 20.9% oxygen. The nearest manual isolation valve is inside the room. The technician is trained for routine maintenance but is not authorized for emergency response. What is the appropriate immediate response?
Correct answer: A - Withdraw, keep others out, and activate the site's emergency response plan.
An oil-injected ammonia screw compressor develops a rising oil temperature at steady load. Oil flow and suction and discharge pressures are unchanged. The thermosyphon cooler's refrigerant outlet, normally a liquid-vapor mixture, now contains superheated vapor at the local outlet pressure. The oil-temperature regulating valve is confirmed in its full-cooling position. Which fault should be investigated first?
Correct answer: C - Inadequate liquid refrigerant circulation through the thermosyphon cooler.
A routine compressor oil report flags an unexpected increase in iron. Viscosity, water content, acid number, bearing temperatures, vibration, and oil differential remain near their established baselines. The sample came from a seldom-used drain whose stagnant contents were not cleared, rather than from the designated sampling point. How should the iron finding be investigated next?
Correct answer: B - Obtain a representative sample from the designated point using the approved procedure.
During a humid afternoon, an evaporative condenser's entering-air wet-bulb temperature and condensing pressure both rise. At the same refrigeration load, the measured difference between refrigerant saturation temperature and entering wet-bulb temperature remains within the unit's established clean-condition range. Fans, spray distribution, and water flow are normal, and operating limits remain satisfied. Which recommendation is justified?
Correct answer: B - Continue monitoring; higher entering wet-bulb temperature explains the pressure rise.
An ammonia liquid line contains a section that can be isolated between two shutoff valves. That section has no effective hydrostatic relief path. It can remain completely liquid-filled while surrounding air warms it, even with all compressors stopped. The design hazard being missed is:
Correct answer: D - Hydraulic overpressure from expansion of liquid with no available expansion space.
A horizontal centrifugal pump takes saturated liquid ammonia from a large recirculator. The liquid surface is 11 ft above the pump centerline, and suction-line losses are 3 ft of liquid at the required flow. Temperature change and velocity at the vessel surface are negligible. At this duty, the pump's required net positive suction head (NPSH) is 6 ft, and the manufacturer requires an additional 3-ft margin. Which assessment is correct?
Correct answer: A - Available NPSH is 8 ft; the specified margin is not met.
A compressor motor is connected directly to a balanced 480-V line-to-line, three-phase supply. At its present load it draws 100 A per line, with a power factor of 0.85 and an efficiency of 90%. For an electrical demand estimate, what power should be attributed to this motor at that operating point?
Correct answer: C - 70.7 kW
In a 120-V three-wire starter circuit, the normally closed STOP and overload contacts are in series with the coil. A normally open auxiliary contact is wired across the momentary START button. The motor runs smoothly while START is held; the contactor releases as soon as START is released. Supply voltage stays at 120 V. The fault is most likely in the:
Correct answer: D - Auxiliary holding circuit, which is failing to complete the parallel path.
A portable ammonia monitor is checked before use with certified, unexpired 100-ppm test gas at the specified flow. The manufacturer's acceptable display range is 90-110 ppm. The monitor stabilizes at 96 ppm, meets its response-time requirement, operates both alarms, and returns to zero in clean air. No full calibration is otherwise due. How should this check be recorded?
Correct answer: D - Calibration check passed; document the readings and retain the monitor in service.
A CO2 system is operating within its approved transcritical envelope. Gas-cooler outlet pressure is 92 bar absolute and outlet temperature is 36 degrees C. CO2's critical point is approximately 73.8 bar absolute and 31.1 degrees C. A commissioning form requests liquid subcooling at this outlet. What entry is technically valid?
Correct answer: C - No valid subcooling value; there is no saturation temperature at this pressure.
The CRST exam also covers these domains. Drill them in the full free practice test:
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