RETA CARO Exam Flashcards

Q: What is the RETA CARO exam pass rate?

RETA does not publicly disclose first-time pass-rate data for the CARO exam. To pass, candidates must score at least 70 (the minimum passing score) out of 100 scored questions; the exam includes 110 total questions (100 scored plus 10 unscored pilot items) and a 3-hour time limit.

Q: How many questions are on the RETA CARO exam?

CARO has 110 multiple-choice questions total: 100 scored questions plus 10 unscored pilot questions used to evaluate future exam content. Candidates get 3 hours to complete the exam, and the minimum passing score is 70.

Q: Do I need work experience to take RETA CARO?

No. RETA CARO is designed as an entry-level credential with no minimum experience requirement, intended for operators who work under the supervision of a more experienced technician. RETA's more advanced CIRO credential requires two years of industrial refrigeration experience.

Q: What ammonia exposure limits should I know for the CARO exam?

Know OSHA's Permissible Exposure Limit (PEL) of 50 ppm as an 8-hour time-weighted average, a Short-Term Exposure Limit (STEL) of 35 ppm over 15 minutes, and NIOSH's Immediately Dangerous to Life or Health (IDLH) value of 300 ppm. Ammonia's odor threshold (roughly 5-50 ppm) gives a self-warning property well below hazardous concentrations.

Q: What regulatory threshold triggers OSHA PSM and EPA RMP for ammonia refrigeration?

Facilities storing 10,000 pounds or more of anhydrous ammonia are covered by OSHA's Process Safety Management standard (29 CFR 1910.119) and EPA's Risk Management Program rule (40 CFR Part 68). PSM protects on-site workers, while RMP focuses on protecting the surrounding community from an accidental release.

Q: Is ammonia flammable?

Yes. Ammonia has a flammable range of roughly 15% to 28% by volume in air (NIOSH Pocket Guide to Chemical Hazards), with an ignition temperature of about 1,204°F. It is harder to ignite than most hydrocarbon refrigerants and is rated a lower-flammability refrigerant, but it still requires an ignition source within its flammable range to burn.

Question 1

Ton of Refrigeration

Accepted Answer

The standard unit of cooling capacity: 12,000 Btu/hr, based on the heat required to melt one ton of ice in 24 hours.

Question 2

Btu (British Thermal Unit)

Accepted Answer

The amount of heat required to raise the temperature of 1 pound of water by 1°F. The base heat-measurement unit used throughout refrigeration calculations.

Question 3

Sensible Heat

Accepted Answer

Heat that changes a substance's temperature without changing its physical state (e.g., cooling liquid ammonia or heating vapor). Measured directly with a thermometer.

Question 4

Latent Heat

Accepted Answer

Heat that changes a substance's state (liquid to vapor or vapor to liquid) at a constant temperature. Latent heat of vaporization is what the evaporator absorbs from the load.

Question 5

Superheat

Accepted Answer

The temperature rise of refrigerant vapor above its saturation temperature at a given pressure, on the low (suction) side. Confirms all liquid has boiled off before vapor reaches the compressor.

Question 6

Subcooling

Accepted Answer

The temperature drop of liquid refrigerant below its saturation temperature at a given pressure, on the high (liquid) side after the condenser. Ensures solid liquid feeds the expansion device.

Question 7

Vapor-Compression Cycle Flow Order

Accepted Answer

Compressor (raises pressure/temp) → Condenser (rejects heat) → Expansion device (drops pressure) → Evaporator (absorbs heat) → back to the compressor.

Question 8

Expansion Device (Metering Device)

Accepted Answer

Meters refrigerant flow into the low side and drops pressure from condensing to evaporating pressure, causing a portion of the liquid to flash into vapor and cool the remaining liquid.

Question 9

Condenser Heat Rejection Balance

Accepted Answer

The condenser must reject the total heat absorbed by the evaporator PLUS the heat of compression added by the compressor. Condenser capacity is always sized above evaporator load.

Question 10

Cascade Refrigeration System

Accepted Answer

Two independent refrigeration circuits linked by a cascade condenser: the high-temperature circuit's evaporator cools the low-temperature circuit's condenser, reaching much lower temperatures than a single ammonia circuit can efficiently reach.

Question 11

Ammonia's ASHRAE Refrigerant Designation

Accepted Answer

R-717 — the '7' prefix marks it as an inorganic refrigerant, and '17' is ammonia's molecular weight (NH3).

Question 12

Ammonia Boiling Point

Accepted Answer

-28°F at atmospheric pressure (0 psig). This is why ammonia systems commonly operate under vacuum at very low evaporator temperatures.

Question 13

Ammonia Flammable Range

Accepted Answer

Roughly 15%-28% ammonia by volume in air (NIOSH Pocket Guide to Chemical Hazards), with an ignition temperature of about 1,204°F. Rated a lower-flammability refrigerant.

Question 14

Ammonia Vapor Density and Odor Threshold

Accepted Answer

Ammonia vapor is lighter than air (relative density about 0.6), so it rises and disperses when released. Its strong odor is detectable at roughly 5-50 ppm, well below hazardous exposure levels, giving a natural warning property.

Question 15

Reading an Ammonia Saturated P-T Table

Accepted Answer

Each pressure corresponds to exactly one saturation temperature at equilibrium. Anchor points to memorize: 0 psig = -28°F (atmospheric boiling point), 0°F ≈ 16 psig, and 68°F ≈ 110 psig. Rising head pressure with a clean condenser signals a real problem such as non-condensables, not a calibration error.

Question 16

Four Compressor Types in Ammonia Refrigeration

Accepted Answer

Reciprocating (pistons, positive displacement, strong at high pressure ratios), Screw/rotary (continuous, oil-flooded rotors, best for high volume), Centrifugal (high-volume, low-pressure-rise, no positive displacement), and Scroll (orbiting spiral, small capacity).

Question 17

Compression Ratio

Accepted Answer

Absolute discharge pressure divided by absolute suction pressure (both in psia, not psig). Higher ratios raise discharge temperature and reduce volumetric efficiency.

Question 18

Volumetric Efficiency

Accepted Answer

The ratio of refrigerant vapor actually pumped by a compressor to its theoretical (swept) displacement. It decreases as compression ratio increases because clearance-volume gas re-expands instead of being discharged.

Question 19

Unloaders

Accepted Answer

Devices that hold reciprocating compressor suction valves open to prevent pumping on selected cylinders, reducing starting load or providing stepped capacity control.

Question 20

Slide Valve

Accepted Answer

The primary capacity-control device on a screw compressor. It also sets the internal volume ratio (Vi), which should be matched to the system's actual compression ratio for efficient operation.

Question 21

Liquid Slugging

Accepted Answer

Liquid ammonia entering the compression chamber instead of vapor. Causes a sharp knocking sound and can destroy valves, pistons, or rotors; usually caused by flood-back from the evaporator or an aggressive defrost.

Question 22

Compressor Discharge Temperature

Accepted Answer

Rises with higher compression ratio and lower suction superheat. Excessive discharge temperature breaks down lubricating oil and risks compressor damage — a key troubleshooting indicator.

Question 23

Short Cycling

Accepted Answer

A compressor starting and stopping too frequently. Common causes include a faulty low-pressure control, an oversized compressor for the load, or a low refrigerant charge.

Question 24

Ammonia-Oil Miscibility

Accepted Answer

Ammonia and refrigeration lubricating oil are NOT miscible (unlike most CFC/HFC systems) — the oil separates from the liquid ammonia rather than dissolving in it, so it must be mechanically returned or periodically drained.

Question 25

Oil Separator

Accepted Answer

A vessel installed just after compressor discharge that removes oil entrained in the hot discharge gas and returns it to the compressor crankcase or system oil reservoir, keeping oil out of the evaporators and condensers.

Question 26

Net Oil Pressure

Accepted Answer

The actual pressure driving lubrication to bearings: oil pump discharge pressure minus crankcase (suction) pressure — not the gauge reading alone. Low net oil pressure triggers a compressor safety trip.

Question 27

Oil Logging

Accepted Answer

Oil accumulating in low-side vessels (evaporators, accumulators, surge drums) because it does not mix with liquid ammonia. Left unchecked, it insulates heat-transfer surfaces and starves the compressor of oil; must be periodically drained.

Question 28

Safe Oil Draining Procedure

Accepted Answer

Isolate the vessel, relieve pressure to a safe low level, wear proper PPE (chemical goggles, gloves, protective clothing), and drain slowly through a dedicated oil pot to avoid a sudden ammonia release.

Question 29

Synthetic vs. Mineral Refrigeration Oil

Accepted Answer

Synthetic oils (e.g., PAG/PAO-based) flow better at low evaporator temperatures and are common in modern ammonia systems. Mineral oils are more traditional but thicken and lose lubricity at very low temperatures.

Question 30

Oil Starvation Symptoms

Accepted Answer

Low net oil pressure, a compressor tripping on its low-oil-pressure safety switch, unusual bearing or piston noise, and rising bearing or discharge temperatures.

Question 31

Oil Charging

Accepted Answer

Oil is added to the compressor crankcase or system oil reservoir under positive pressure using an oil pump or pressurized charging drum — the system is never opened to atmosphere while pressurized.

Question 32

DX (Direct Expansion) Evaporator

Accepted Answer

Refrigerant flow is metered by a TXV that controls the superheat leaving the coil. Uses a smaller ammonia charge and simpler controls than a flooded system; common on smaller units.

Question 33

Flooded Evaporator

Accepted Answer

The coil stays liquid-full, with level controlled by a float or surge drum rather than superheat. Higher heat-transfer efficiency than DX; common on large industrial systems.

Question 34

TXV (Thermostatic Expansion Valve)

Accepted Answer

Senses suction line superheat through a sensing bulb and (usually) an external equalizer, then modulates refrigerant flow into the evaporator to hold a set superheat.

Question 35

Accumulator (Suction Trap)

Accepted Answer

A vessel installed ahead of the compressor suction line that traps any liquid ammonia carryover from the evaporator, protecting the compressor from slugging.

Question 36

Frost Buildup and Defrost

Accepted Answer

Frost on an evaporator coil insulates the surface and reduces heat transfer and cooling capacity. Defrost (hot gas, water, electric, or air) removes the frost and restores performance; hot gas defrost routes discharge gas back through the coil.

Question 37

Evaporative Condenser

Accepted Answer

Rejects heat using both a water spray and forced airflow across the coil. The most common and most efficient condenser type in industrial ammonia plants.

Question 38

Air-Cooled Condenser

Accepted Answer

Rejects heat using fans and airflow only, with no water spray. Simpler and lower-maintenance than evaporative condensers, but less efficient in hot climates.

Question 39

Condenser Approach Temperature

Accepted Answer

The difference between condensing temperature and outdoor wet-bulb (evaporative) or dry-bulb (air-cooled) temperature. A rising approach with clean coils and good airflow points to non-condensables or overcharge.

Question 40

High-Pressure Receiver

Accepted Answer

A vessel that stores liquid ammonia after the condenser, buffering the system's refrigerant charge to handle varying loads and maintain a steady liquid feed to the low side.

Question 41

King Valve

Accepted Answer

The main liquid outlet (shutoff) valve on the high-pressure receiver, used to isolate the receiver's liquid ammonia from the rest of the system.

Question 42

Pressure Relief Valve

Accepted Answer

A safety device that automatically vents excess pressure from a vessel to atmosphere or a flare/relief header once the set pressure is exceeded. Sized, installed, and tested per ASME and IIAR requirements.

Question 43

Non-Condensables

Accepted Answer

Air or other gases trapped in an ammonia system that will not condense at normal condenser conditions. They raise head pressure and reduce condenser efficiency even when charge and airflow are otherwise normal.

Question 44

Automatic Purger

Accepted Answer

A device, usually near the condenser or receiver high point, that periodically collects and vents accumulated non-condensable gas while minimizing ammonia loss. Purge logs should be checked regularly to catch chronic air in-leakage.

Question 45

Ammonia PEL (Permissible Exposure Limit)

Accepted Answer

OSHA's 8-hour time-weighted average exposure limit for ammonia: 50 ppm.

Question 46

Ammonia STEL (Short-Term Exposure Limit)

Accepted Answer

35 ppm as a 15-minute short-term exposure limit — the maximum average concentration workers may be exposed to for a brief period.

Question 47

Ammonia IDLH

Accepted Answer

300 ppm — NIOSH's Immediately Dangerous to Life or Health concentration. Only self-contained breathing apparatus (SCBA) may be used at or above this level, never a filtering respirator.

Question 48

OSHA PSM / EPA RMP Threshold Quantity

Accepted Answer

10,000 pounds of anhydrous ammonia on-site triggers coverage under OSHA's Process Safety Management standard (29 CFR 1910.119) and EPA's Risk Management Program rule (40 CFR Part 68).

Question 49

SCBA Requirement

Accepted Answer

Self-contained breathing apparatus is required for entry into any atmosphere at or above the IDLH (300 ppm for ammonia); air-purifying (cartridge/filter) respirators are not adequate at these concentrations.

Question 50

IIAR Ammonia Standards

Accepted Answer

IIAR 2 covers safe design of closed-circuit systems, IIAR 6 covers inspection/testing/maintenance, IIAR 7 covers developing operating procedures, and IIAR 9 covers minimum safety criteria for existing systems.

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