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The CARO exam has 110 questions and runs 3 hours.
These 10 free CARO questions are organized by exam domain, so you can see how each part of the Certified Assistant Refrigeration Operator blueprint is tested. Reveal the answer and explanation under each question.
An ice-making batch must turn 600 lb of water at 52°F into ice at 32°F in two hours. Use 1.0 Btu/(lb·°F) for water's specific heat and 144 Btu/lb for its latent heat of freezing. Ignore the containers and heat gain from the surroundings. What average refrigeration duty is required for the batch?
Correct answer: C - 49,200 Btu/h
Saturated liquid ammonia enters an insulated expansion valve and leaves at lower pressure as a liquid-vapor mixture. Flow is steady, and changes in velocity and elevation are negligible. Which statement correctly describes the process through the valve?
Correct answer: D - Specific enthalpy stays approximately constant while some of the liquid flashes.
A fixed-speed rotary screw compressor reduces capacity by moving its capacity slide valve. Which internal mechanism produces this unloading?
Correct answer: B - Part of the trapped vapor is bypassed back to suction.
At steady operating temperature, a reciprocating ammonia compressor has an oil-pump discharge pressure of 76 psig and a crankcase pressure of 31 psig. Its specified acceptable net oil pressure is 35-60 psi, referenced to the crankcase. All other readings are normal. What does the lubrication-pressure check show?
Correct answer: A - 45 psi, within the specified range; continue normal monitoring.
Routine oil analyses from one compressor showed rising iron concentrations over three samples. The next sample, taken shortly after a large addition of fresh approved oil, shows a sharp drop. The sampling method and laboratory are unchanged, and no mechanical repair has been made. What is the soundest use of this new result?
Correct answer: A - Account for makeup-oil dilution before judging the wear trend.
During a round on a pumped liquid-overfeed ammonia system, an operator observes liquid and vapor returning from an evaporator to the low-pressure separator. Separator level is stable, cooling is on target, and the compressor receives vapor without evidence of liquid carryover. The appropriate response to this wet return is to:
Correct answer: D - Maintain operation; the separator normally receives a two-phase return.
An evaporative condenser runs at higher head pressure on a humid day, although refrigeration load and outdoor dry-bulb temperature match yesterday's conditions. Its fans and water distribution are operating normally. Which air measurement is the correct ambient reference for checking the condenser's rated heat-rejection performance?
Correct answer: C - Entering-air wet-bulb temperature.
Two calibrated pressure gauges agree on a high-side ammonia vessel that has been shut down long enough for its liquid and vapor to reach the same uniform temperature. Both gauges, expressed in absolute pressure, read above the R717 saturation pressure at that temperature. Which condition best explains the pressure excess?
Correct answer: C - Noncondensable gas in the vapor space.
An operator splashes liquid ammonia into one eye and immediately reaches a functioning eyewash in an uncontaminated area. A coworker is calling emergency medical services. Which first-aid action should begin without waiting for that call to finish?
Correct answer: B - Irrigate the eye continuously with water, holding the eyelids open.
Before servicing a compressor coupling, an authorized mechanic has controlled all non-electrical energy sources and verified that they cannot reaccumulate. The motor is stopped, and the local selector switch is padlocked in OFF, but the power disconnect is still closed. What additional action is necessary to control the motor's energy supply?
Correct answer: D - Open and lock the disconnect, then verify effective isolation.
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