RETA Certified Assistant Refrigeration Operator (CARO) — Questions and Answers

Question 1: During a large ammonia release, how should non-responding employees evacuate?

Downwind toward the release
Into the machinery room for shelter
Toward the lowest point of the building
Upwind or crosswind to the designated assembly point (Correct answer)

Correct answer: Upwind or crosswind to the designated assembly point

Evacuating upwind or crosswind keeps people out of the plume and moves them to a safe assembly point.

Question 2: In a gravity-flooded evaporator, where is the surge drum normally located?

Below the evaporator coil
Next to the condenser
Inside the high-pressure receiver
Above the evaporator coil (Correct answer)

Correct answer: Above the evaporator coil

The drum sits above the coil so liquid can flow by gravity into the coil and vapor can rise back to the drum.

Question 3: What is the CERCLA/EPCRA reportable quantity for an anhydrous ammonia release within 24 hours?

500 pounds
100 pounds (Correct answer)
1,000 pounds
10 pounds

Correct answer: 100 pounds

A release of 100 pounds or more of ammonia in 24 hours must be reported to the National Response Center and to state and local authorities.

Question 4: What is the function of an automatic purger in an ammonia refrigeration system?

Remove non-condensable gases such as air from the system (Correct answer)
Defrost evaporator coils
Add refrigerant charge automatically
Drain oil from the low side

Correct answer: Remove non-condensable gases such as air from the system

Automatic purgers remove air and other non-condensables that raise condensing pressure and waste energy.

Question 5: In a hot gas defrost system, what heat source melts the frost from the evaporator coil?

Warm condenser cooling water sprayed on the coil
Electric heaters mounted on the drain pan only
Compressor discharge vapor routed into the coil (Correct answer)
Outdoor air drawn through the coil

Correct answer: Compressor discharge vapor routed into the coil

Hot gas defrost sends high-pressure discharge vapor into the coil, where it condenses and releases heat.

Question 6: An operator gets liquid ammonia splashed in the eyes. What is the correct first-aid action?

Rub the eyes gently to remove the liquid
Cover the eyes with a dry bandage and wait for EMS
Flush with clean water for at least 15 minutes (Correct answer)
Apply a neutralizing vinegar solution

Correct answer: Flush with clean water for at least 15 minutes

Immediate, continuous flushing with water for at least 15 minutes is the standard first aid for ammonia eye exposure.

Question 7: A pressure relief valve on an ammonia vessel has been found to have a small weeping/dripping of refrigerant. What should the operator do?

Apply pipe sealant to stop the weep
Tighten the valve spring to stop the leak
Leave it alone as minor weeping is normal
Tag the valve out of service, install a second relief valve if required by code, and arrange for immediate replacement of the leaking valve (Correct answer)

Correct answer: Tag the valve out of service, install a second relief valve if required by code, and arrange for immediate replacement of the leaking valve

A weeping relief valve should be replaced promptly — it may not reseat properly and could fail to protect at the correct pressure; follow your jurisdiction's code requirements for maintaining pressure relief protection during valve replacement.

Question 8: What material is most commonly used for ammonia refrigeration piping in industrial systems?

PVC pipe
Aluminum tubing
Carbon steel pipe (Correct answer)
Copper tubing

Correct answer: Carbon steel pipe

Carbon steel pipe is the standard material for ammonia refrigeration because ammonia is incompatible with copper, brass, and zinc, which corrode rapidly in its presence.

Question 9: What is the primary purpose of a crankcase heater on a reciprocating compressor?

To raise discharge pressure during startup
To keep the oil warm and limit refrigerant migration into the crankcase during the off cycle (Correct answer)
To preheat suction gas before compression
To prevent the motor windings from freezing

Correct answer: To keep the oil warm and limit refrigerant migration into the crankcase during the off cycle

Crankcase heaters keep oil warmer than the coldest point in the system so refrigerant does not condense and dilute the oil while the compressor is off.

Question 10: What is subcooling and why is it beneficial in a refrigeration system?

Reducing suction superheat for better heat transfer
Cooling liquid refrigerant below its saturation temperature to increase system capacity and prevent flash gas (Correct answer)
Cooling vapor below dew point to improve suction line efficiency
Lowering discharge temperature to reduce compressor wear

Correct answer: Cooling liquid refrigerant below its saturation temperature to increase system capacity and prevent flash gas

Subcooling cools liquid refrigerant below its condensing temperature, increasing the system's net refrigerating effect and preventing flash gas in the liquid line.

Question 11: Excessive vibration in a reciprocating ammonia compressor is best diagnosed using which method?

Monitoring suction temperature
Checking refrigerant charge level
Visual inspection combined with vibration analysis and listening for unusual mechanical noises (Correct answer)
Checking system pressures only

Correct answer: Visual inspection combined with vibration analysis and listening for unusual mechanical noises

Vibration analysis and listening for unusual sounds (knocking, rattling) combined with visual inspection help identify loose mounts, worn bearings, valve issues, or liquid slugging causing the vibration.

Question 12: Why is vibration data on compressors and pumps trended over time rather than checked only once?

To determine the refrigerant's saturation temperature
To satisfy the electric utility's demand requirements
To detect gradual changes that signal developing bearing, alignment, or balance problems (Correct answer)
To calculate refrigerant charge

Correct answer: To detect gradual changes that signal developing bearing, alignment, or balance problems

Trending reveals changes from a baseline, allowing repairs before a failure occurs.

Question 13: Why does a flooded evaporator generally transfer heat better than a DX evaporator of the same size?

Its refrigerant is always superheated
It runs at a higher condensing pressure
It uses no surge drum
Nearly all of its internal surface is wetted with liquid refrigerant (Correct answer)

Correct answer: Nearly all of its internal surface is wetted with liquid refrigerant

Liquid-wetted surfaces have far higher heat transfer coefficients than surfaces contacting superheated vapor.

Question 14: What is the main function of a high-pressure receiver in a refrigeration system?

Superheat vapor before the compressor
Remove noncondensable gases
Store liquid refrigerant leaving the condenser (Correct answer)
Separate oil from discharge gas

Correct answer: Store liquid refrigerant leaving the condenser

The receiver holds liquid refrigerant and absorbs charge fluctuations as load changes.

Question 15: Why might a reciprocating compressor crankcase heater be used during the off cycle?

To raise discharge pressure
To boil off refrigerant that has migrated into the oil, preventing foaming at startup (Correct answer)
To cool the oil
To purge noncondensables

Correct answer: To boil off refrigerant that has migrated into the oil, preventing foaming at startup

Keeping the crankcase warm limits refrigerant dissolved in the oil, which reduces foaming and oil loss at startup.

Question 16: What type of heat does refrigerant primarily absorb as it boils in the evaporator?

Latent heat of vaporization (Correct answer)
Heat of compression
Sensible heat
Latent heat of fusion

Correct answer: Latent heat of vaporization

Boiling is a change of state, so most of the heat absorbed is latent heat of vaporization.

Question 17: What is the function of an oil pressure safety switch on an ammonia compressor?

To shut down the compressor if oil pressure falls below a safe minimum (Correct answer)
To monitor refrigerant purity
To maintain refrigerant charge
To regulate discharge temperature

Correct answer: To shut down the compressor if oil pressure falls below a safe minimum

The oil pressure safety switch monitors lubrication oil pressure and trips the compressor off if pressure drops below the minimum required to protect compressor bearings.

Question 18: Why is preventive maintenance critical in refrigeration systems?

To allow unplanned shutdowns
To extend equipment lifespan (Correct answer)
To reduce staff training
To maximize repair costs

Correct answer: To extend equipment lifespan

Preventive maintenance is critical in refrigeration systems because it helps identify and address minor issues before they escalate into major failures. Regular inspections, cleaning, and adjustments reduce wear and tear, optimize system performance, and significantly extend the operational lifespan of expensive refrigeration equipment. This proactive approach ultimately saves on costly repairs and replacements.

Question 19: What two things happen to refrigerant as it passes through the expansion (metering) device?

Pressure drops and part of the liquid flashes to vapor (Correct answer)
Pressure stays constant and temperature rises
Pressure rises and the liquid subcools
Pressure drops and all of the liquid condenses

Correct answer: Pressure drops and part of the liquid flashes to vapor

The sudden pressure drop causes some liquid to flash, cooling the remaining liquid to evaporator temperature.

Question 20: In an ammonia plant, what is the purpose of a thermosiphon oil cooler on a screw compressor?

Separate oil from refrigerant vapor
Heat oil before start-up
Cool compressor oil using liquid refrigerant circulated by natural convection (Correct answer)
Return oil from the low side

Correct answer: Cool compressor oil using liquid refrigerant circulated by natural convection

Thermosiphon oil coolers use liquid ammonia from the receiver that boils in the cooler and returns by gravity and density difference.

Question 21: An evaporative condenser rejects heat mainly by which process?

Evaporation of water sprayed over the coil (Correct answer)
Radiation to the sky
Direct contact between refrigerant and water
Conduction to the building structure

Correct answer: Evaporation of water sprayed over the coil

Water evaporating on the coil surface carries away large amounts of latent heat.

Question 22: What does a continuously running compressor that never shuts off, combined with a warm refrigerated space, most likely indicate?

Insufficient refrigeration capacity — possible refrigerant loss, dirty coils, or excessive load (Correct answer)
Normal operation under peak summer conditions
Oversized compressor
The thermostat setpoint is too low

Correct answer: Insufficient refrigeration capacity — possible refrigerant loss, dirty coils, or excessive load

A compressor that runs continuously without achieving the setpoint indicates the system lacks sufficient capacity, which may be due to refrigerant loss, fouled heat exchangers, or an unusually high heat load.

Question 23: Which oil type is commonly used with HFC refrigerants because of miscibility requirements?

Mineral oil
Vegetable oil
Polyolester (POE) oil (Correct answer)
Hydraulic fluid

Correct answer: Polyolester (POE) oil

HFC refrigerants are not miscible with mineral oil, so POE oils are usually used for proper oil return.

Question 24: What is the effect of a higher condensing pressure on system performance?

Increased capacity and lower power use
No change in capacity or power
Lower discharge temperature
Reduced capacity and higher power per ton (Correct answer)

Correct answer: Reduced capacity and higher power per ton

Higher head pressure raises the compression ratio, cutting capacity and increasing energy use.

Question 25: Why are routine oil analyses done on large industrial compressors?

To check the condenser water treatment
To set the purger timer
To find wear metals, moisture, and oil breakdown before a failure happens (Correct answer)
To measure the ammonia charge

Correct answer: To find wear metals, moisture, and oil breakdown before a failure happens

Lab oil analysis shows the oil condition and internal wear trends so problems can be fixed early.

Question 26: Which condition will most likely cause an excessively high compressor discharge temperature?

Liquid floodback
High suction pressure with low superheat
Low compression ratio
High compression ratio combined with high suction superheat (Correct answer)

Correct answer: High compression ratio combined with high suction superheat

Large compression ratios and hot suction gas both raise the temperature of the gas leaving the compressor.

Question 27: After completing maintenance on an ammonia system, how should the technician confirm there are no refrigerant leaks before restarting?

Use electronic ammonia leak detector or sulfur stick test, and check all joints at operating pressure (Correct answer)
Pressurize with nitrogen and check pressure drop over 24 hours only
Visual inspection of all fittings is sufficient
Smell for ammonia odor only

Correct answer: Use electronic ammonia leak detector or sulfur stick test, and check all joints at operating pressure

Electronic leak detectors or sulfur sticks (which produce white smoke with ammonia) should be used to check all opened connections at operating pressure, as visual inspection alone cannot detect small leaks.

Question 28: At atmospheric pressure, approximately what is the boiling point of ammonia (R-717)?

-41°F
32°F
-15°F
-28°F (Correct answer)

Correct answer: -28°F

Ammonia boils at about -28°F (-33°C) at 14.7 psia.

Question 29: What is superheat in a refrigeration system, and where is it measured?

The temperature of refrigerant vapor above its saturation temperature, measured at the evaporator outlet (Correct answer)
The subcooling temperature, measured at the liquid line
The heat added by the compressor, measured at discharge
The temperature difference between condensing and ambient, measured at the condenser

Correct answer: The temperature of refrigerant vapor above its saturation temperature, measured at the evaporator outlet

Superheat is the degrees of temperature a refrigerant vapor has above its saturation point, and it is measured at the evaporator outlet to ensure no liquid enters the compressor.

Question 30: An operator measures a condenser pressure that is well above the saturation pressure for the liquid temperature leaving the condenser. What does this most likely indicate?

Noncondensable gases are present (Correct answer)
The system is short of refrigerant
The evaporator is overfed
The oil separator is working correctly

Correct answer: Noncondensable gases are present

Pressure above the saturation pressure at the measured temperature points to air or other noncondensables in the condenser.

Question 31: According to the ASHRAE refrigerant safety classification system, what does the designation 'B2L' indicate about a refrigerant like ammonia (R-717)?

Lower toxicity, higher flammability
Lower toxicity, mildly flammable
Higher toxicity, mildly flammable (Correct answer)
Higher toxicity, no flame propagation

Correct answer: Higher toxicity, mildly flammable

The ASHRAE safety classification is a two-part code. The letter (A or B) indicates toxicity, where 'A' is lower toxicity and 'B' is higher toxicity. The number (1, 2, 2L, or 3) indicates flammability. '2L' specifically designates a refrigerant as 'mildly flammable,' meaning it has low burning velocity and requires significant energy to ignite. Therefore, B2L means higher toxicity and mild flammability.

Question 32: Under EPCRA Sections 311/312, the annual Tier II hazardous chemical inventory report is due by what date?

January 1
July 1
December 31
March 1 (Correct answer)

Correct answer: March 1

Tier II reports covering the previous calendar year are due by March 1 each year.

Question 33: A worker gets liquid ammonia splashed in their eyes. What is the correct first-aid action?

Cover the eyes with a dry bandage and wait for EMS
Rinse briefly and apply eye drops
Flush with clean water for at least 15 minutes (Correct answer)
Apply a neutralizing vinegar solution

Correct answer: Flush with clean water for at least 15 minutes

Immediate, prolonged flushing with water for at least 15 minutes is the accepted first aid for ammonia eye exposure.

Question 34: Which agency issues and enforces the Clean Air Act 112(r) RMP regulations?

OSHA
NFPA
EPA (Correct answer)
DOT

Correct answer: EPA

The EPA administers the Risk Management Program under 40 CFR Part 68.

Question 35: Raising the evaporator (suction) pressure while keeping condensing pressure constant generally does what?

Increases compression ratio
Has no effect on capacity
Decreases capacity and efficiency
Increases capacity and improves efficiency (Correct answer)

Correct answer: Increases capacity and improves efficiency

Higher suction pressure means denser suction gas and a lower compression ratio, improving capacity and efficiency.

Question 36: Which maintenance strategy uses condition-monitoring data, such as vibration or oil analysis, to schedule repairs before failure?

Predictive maintenance (Correct answer)
Reactive maintenance
Run-to-failure maintenance
Emergency maintenance

Correct answer: Predictive maintenance

Predictive maintenance bases its actions on the measured condition of equipment.

Question 37: An automatic purger is usually connected to which points in the system?

Evaporator oil drain points
Purge points at the tops of condensers and high-pressure receivers (Correct answer)
The compressor suction strainer
The low-side liquid line

Correct answer: Purge points at the tops of condensers and high-pressure receivers

Purgers sample gas from high-side points where noncondensables collect, such as condenser outlets and receiver tops.

Question 38: An operator notices a strong ammonia odor in the engine room, but the permanently installed ammonia detectors have not gone into alarm. Which of the following statements is the most accurate explanation for this situation?

The odor threshold for ammonia is very low, and it can be easily detected by smell well below the concentration required to trigger a low-level alarm. (Correct answer)
The human nose is less sensitive to ammonia than electronic detectors, so it must be a false alarm.
The ammonia concentration is likely above the Upper Explosive Limit (UEL) and therefore too rich to be detected.
The detectors are likely malfunctioning and should be ignored until the next scheduled calibration.

Correct answer: The odor threshold for ammonia is very low, and it can be easily detected by smell well below the concentration required to trigger a low-level alarm.

Ammonia has a very low odor threshold, typically detectable by humans at concentrations around 5 parts per million (ppm). Safety alarm systems are set at much higher concentrations, often with a low-level alarm at 25-50 ppm (the TWA-TLV) and high-level alarms at 150 ppm or more. Therefore, it is common to smell ammonia before a detector alarms, serving as an early warning of a small leak.

Question 39: What is the role of the evaporator in a refrigeration system?

Absorb heat and cool air (Correct answer)
Increase refrigerant pressure
Reject heat to ambient
Filter refrigerant

Correct answer: Absorb heat and cool air

The evaporator's role in a refrigeration system is to absorb heat from the space or substance being cooled. Low-pressure liquid refrigerant enters the evaporator, where it boils and changes into a low-pressure vapor by absorbing heat from the surrounding air or liquid. This process effectively cools the desired area.

Question 40: When ammonia dissolves in water, what compound is formed?

Hydrogen sulfide
Ammonium chloride
Ammonium hydroxide (Correct answer)
Nitric acid

Correct answer: Ammonium hydroxide

Ammonia combines with water to form ammonium hydroxide, a caustic alkaline solution.

Question 41: Which valve is recommended on the final drain point of an ammonia oil drain?

A globe valve chained in the open position
A spring-loaded self-closing (dead-man) valve (Correct answer)
A check valve
A pressure relief valve

Correct answer: A spring-loaded self-closing (dead-man) valve

A self-closing valve shuts automatically if the operator lets go, which limits ammonia release during draining.

Question 42: Which condition is most likely if non-condensable gases accumulate in an ammonia condenser?

Abnormally high condensing (head) pressure (Correct answer)
Increased system capacity
Decreased compressor power use
Abnormally low discharge pressure

Correct answer: Abnormally high condensing (head) pressure

Non-condensables add their partial pressure and blanket heat transfer surfaces, raising head pressure and energy use.

Question 43: Under OSHA's Process Safety Management standard (1910.119), what quantity of anhydrous ammonia triggers PSM coverage?

50,000 lb
1,000 lb
500 lb
10,000 lb (Correct answer)

Correct answer: 10,000 lb

Facilities with more than 10,000 lb of anhydrous ammonia in a process are covered by PSM.

Question 44: What is the most reliable reference for the correct running oil level in a reciprocating compressor sight glass?

The level observed when the compressor was last shut down
A full sight glass at all times
The compressor manufacturer's specifications (Correct answer)
The level recorded by the previous shift, regardless of conditions

Correct answer: The compressor manufacturer's specifications

Correct oil level varies by machine design, so the manufacturer's specification is the authoritative reference.

Question 45: How can air most commonly enter an ammonia system?

Through the oil separator return line
Through the water bubbler
Through the high-pressure side when it runs above atmospheric pressure
Through leaks in parts of the system running below atmospheric pressure (vacuum) (Correct answer)

Correct answer: Through leaks in parts of the system running below atmospheric pressure (vacuum)

Low-side parts that run in a vacuum can pull air in through leaking seals, valve packings, and fittings.

Question 46: What is the EPA Risk Management Program (RMP) threshold quantity for anhydrous ammonia in a process?

5,000 pounds
500 pounds
10,000 pounds (Correct answer)
20,000 pounds

Correct answer: 10,000 pounds

Processes holding more than 10,000 pounds of anhydrous ammonia are subject to the EPA RMP rule under Clean Air Act Section 112(r).

Question 47: A screw compressor is consistently tripping on its high-temperature safety cutout. The condenser appears to be operating normally, and the refrigerant charge is correct. Which of the following maintenance issues is the most likely cause?

A partially closed suction service valve
A malfunctioning capacity slide valve
A dirty or clogged oil cooler/filter (Correct answer)
Excessive non-condensable gases

Correct answer: A dirty or clogged oil cooler/filter

In a screw compressor, oil is used not only for lubrication but also for cooling and sealing the rotors. If the oil cooler or oil filter is dirty or clogged, oil flow will be restricted, and its cooling efficiency will be greatly reduced. This leads to the compressor overheating and tripping the high-temperature safety control.

Question 48: High evaporator superheat combined with low suction pressure usually indicates what condition?

Starved evaporator from low charge or restricted feed (Correct answer)
Dirty condenser
Overcharged system
Excessive load on the evaporator

Correct answer: Starved evaporator from low charge or restricted feed

Too little refrigerant feed makes it boil off early, leaving excess superheat and low suction pressure.

Question 49: A low-pressure controller on an ammonia system is set to cut out at a specific suction pressure. What does a cut-in pressure setting represent?

The discharge pressure limit
The pressure at which the compressor restarts after a low-pressure shutdown (Correct answer)
The oil pressure safety setpoint
The pressure at which the compressor shuts down

Correct answer: The pressure at which the compressor restarts after a low-pressure shutdown

The cut-in pressure is the suction pressure at which the low-pressure controller closes and allows the compressor to restart after conditions have returned to acceptable levels.

Question 50: In a hot gas defrost system, what is used to melt frost from the evaporator?

Electric heaters only
Hot compressor discharge vapor (Correct answer)
Warm condenser cooling water
Subcooled liquid from the receiver

Correct answer: Hot compressor discharge vapor

Discharge gas is routed into the evaporator, where it condenses and releases heat to melt the frost.

Question 51: What is the main operating penalty of running a refrigeration system at a higher-than-necessary condensing pressure?

Increased compressor power per ton of refrigeration (Correct answer)
Lower discharge temperature
Higher evaporator capacity
Reduced risk of oil carryover

Correct answer: Increased compressor power per ton of refrigeration

A higher compression ratio requires more horsepower per ton and lowers efficiency.

Question 52: Frequent compressor short cycling on and off is harmful mainly because it:

Reduces refrigerant charge
Causes excessive motor starts, overheating windings and increasing wear (Correct answer)
Improves oil return too much
Lowers condenser pressure

Correct answer: Causes excessive motor starts, overheating windings and increasing wear

Every start draws high inrush current and puts stress on parts, so frequent cycling shortens motor and compressor life.

Question 53: Which component protects a compressor from liquid slugging by separating liquid from returning suction vapor?

Oil separator
Suction accumulator or low-pressure receiver (Correct answer)
King valve
High-pressure receiver

Correct answer: Suction accumulator or low-pressure receiver

Accumulators and low-pressure receivers trap liquid so only vapor reaches the compressor suction.

Question 54: What does a liquid level indicator (sight glass) on an ammonia receiver tell the operator?

Suction superheat level
The amount of liquid refrigerant in the vessel (Correct answer)
Refrigerant purity
Oil contamination level

Correct answer: The amount of liquid refrigerant in the vessel

A sight glass or liquid level indicator shows the operator the quantity of liquid refrigerant in the receiver, ensuring adequate charge without overfilling.

Question 55: A system runs at 150 psig discharge and 15 psig suction at sea level. What is the approximate compression ratio?

5.5 (Correct answer)
10.0
6.3
4.8

Correct answer: 5.5

Using absolute pressures, 164.7 psia ÷ 29.7 psia ≈ 5.5.

Question 56: When isolating a section of refrigeration piping for repairs, the correct procedure is to:

Close the isolation valves, then immediately open flanges and cut pipe
Pressurize the isolated section with nitrogen before cutting to purge refrigerant
Close isolation valves, relieve trapped pressure safely, verify pressure is zero, then open the line (Correct answer)
Remove the relief valve from the section first, then close the isolation valves

Correct answer: Close isolation valves, relieve trapped pressure safely, verify pressure is zero, then open the line

After closing isolation valves, any trapped refrigerant must be safely relieved and pressure verified at zero before opening piping, to prevent sudden release of pressurized refrigerant or ammonia exposure.

Question 57: Why is a pressure relief valve required on a condenser or other pressure vessel that can be isolated?

To purge non-condensables automatically
To protect it from over-pressure, such as from fire or heat with valves closed (Correct answer)
To control normal condensing pressure
To regulate liquid flow to the receiver

Correct answer: To protect it from over-pressure, such as from fire or heat with valves closed

Relief valves vent refrigerant if pressure exceeds the vessel's design limit, preventing rupture.

Question 58: Most people can smell ammonia at roughly what concentration?

About 5 ppm (Correct answer)
About 1,000 ppm
About 15%
About 300 ppm

Correct answer: About 5 ppm

Ammonia's odor threshold is around 5 ppm, well below harmful levels, which makes it self-alarming.

Question 59: Which piece of information must a facility keep on hand to support EPCRA Tier II reporting for ammonia?

The building's lease agreement
The compressor warranty
The Safety Data Sheet (SDS) (Correct answer)
The electrical one-line diagram

Correct answer: The Safety Data Sheet (SDS)

EPCRA Section 311 is built on SDS availability, and SDS data supports accurate hazardous chemical inventory reporting.

Question 60: Non-condensable gases trapped in a condenser most directly cause which problem?

Abnormally high head pressure (Correct answer)
Excess liquid in the evaporator
Reduced oil in the crankcase
Low discharge temperature

Correct answer: Abnormally high head pressure

Non-condensables occupy condenser surface and add their partial pressure, raising head pressure.

Question 61: A V-belt drive is being checked during routine maintenance. What is the common rule of thumb for proper belt deflection?

1/4 inch per inch of span
1 inch regardless of span
1/64 inch per inch of span (Correct answer)
No deflection at all

Correct answer: 1/64 inch per inch of span

A deflection of about 1/64 inch per inch of span is the widely used guideline for V-belt tension.

Question 62: Why is EPA Section 608's refrigerant recovery and certification program generally not the main compliance framework for ammonia systems?

Ammonia systems are too small to be covered
Section 608 focuses on ozone-depleting and HFC substitute refrigerants, and ammonia is exempt from its venting prohibition (Correct answer)
Section 608 only applies to vehicles
Ammonia is regulated only by the FDA

Correct answer: Section 608 focuses on ozone-depleting and HFC substitute refrigerants, and ammonia is exempt from its venting prohibition

Section 608 targets halocarbon refrigerants, and ammonia is exempt from its venting prohibition, though other laws still restrict ammonia releases.

Question 63: What protective suit level is required when there is a high potential for skin contact with liquid ammonia and the highest respiratory protection?

Level D
Level C
Level B
Level A (Correct answer)

Correct answer: Level A

Level A provides a fully encapsulating vapor-tight suit with SCBA, the highest level of protection.

Question 64: Why is closing valves on both ends of a liquid-full ammonia line segment dangerous?

It allows noncondensables to collect
Liquid expansion from warming can generate pressures high enough to rupture the pipe (Correct answer)
It lowers suction pressure and frosts the compressor
It causes oil to foul the evaporator

Correct answer: Liquid expansion from warming can generate pressures high enough to rupture the pipe

Trapped liquid expands as it warms (hydrostatic lockup) and can build enough pressure to burst piping or valves.

Question 65: What does an electronic expansion valve (EEV) use to adjust its opening?

A controller signal driving a stepper motor or pulse-width modulated actuator (Correct answer)
A float ball in the evaporator
A temperature bulb filled with refrigerant
A fixed orifice size

Correct answer: A controller signal driving a stepper motor or pulse-width modulated actuator

EEVs use sensors and a controller to position the valve electronically for precise superheat or level control.

Question 66: What problem can result from over-greasing an electric motor bearing?

Longer bearing life in all cases
Overheating and possible seal or winding damage (Correct answer)
Lower motor amperage
Improved cooling of the bearing

Correct answer: Overheating and possible seal or winding damage

Excess grease increases friction and heat and can be forced into the windings.

Question 67: The primary purpose of the expansion valve (or metering device) in the refrigeration cycle is to:

Filter contaminants and moisture from the liquid refrigerant.
Create a large pressure drop, which reduces the refrigerant's boiling point. (Correct answer)
Pump the liquid refrigerant from the condenser to the evaporator.
Increase the refrigerant's temperature to assist in heat rejection.

Correct answer: Create a large pressure drop, which reduces the refrigerant's boiling point.

The expansion valve meters the flow of liquid refrigerant into the evaporator and creates a significant pressure drop. This sudden drop in pressure lowers the refrigerant's saturation temperature (boiling point) to a level where it can absorb heat from the refrigerated space.

Question 68: Which of the following is a primary thermodynamic property of ammonia (R-717) that makes it a highly efficient refrigerant for large industrial systems?

Compatibility with copper and brass piping
High latent heat of vaporization (Correct answer)
High miscibility with mineral oil
High Global Warming Potential (GWP)

Correct answer: High latent heat of vaporization

Ammonia (R-717) has a very high latent heat of vaporization, meaning it can absorb a large amount of heat per unit of mass as it changes from a liquid to a gas in the evaporator. This property makes the refrigeration cycle more efficient, requiring less refrigerant to be circulated to achieve the desired cooling effect, which is particularly advantageous in large-scale industrial applications.

Question 69: Flash gas formed at the expansion device serves what purpose in the cycle?

It raises the evaporator pressure
It increases the refrigerating effect per pound
It cools the remaining liquid down to evaporator temperature (Correct answer)
It lubricates the expansion valve

Correct answer: It cools the remaining liquid down to evaporator temperature

The portion that flashes absorbs heat from the remaining liquid, dropping it to the evaporator saturation temperature.

Question 70: If the pressure in an evaporator is lowered, what happens to the refrigerant's saturation (boiling) temperature?

It becomes equal to the condensing temperature
It rises
It stays the same
It drops (Correct answer)

Correct answer: It drops

Saturation temperature is directly tied to pressure, so lower pressure means a lower boiling point.

Question 71: Why are purge points usually purged one at a time instead of all at once?

So the purger can focus on the point with the most air and avoid pulling mostly ammonia (Correct answer)
Because purging all points at once raises suction pressure
It is required to keep the oil warm
So the condenser fans can be shut off

Correct answer: So the purger can focus on the point with the most air and avoid pulling mostly ammonia

Sequencing through the points one at a time lets the purger draw air-rich gas from each location more effectively.

Question 72: A thermostatic expansion valve (TXV) senses which two conditions to regulate refrigerant flow?

Compressor speed and refrigerant charge
Discharge temperature and condenser pressure
Evaporator outlet temperature and suction pressure (Correct answer)
Suction pressure and oil level

Correct answer: Evaporator outlet temperature and suction pressure

The TXV uses a sensing bulb at the evaporator outlet and an external equalizer sensing suction pressure to maintain a constant superheat and regulate refrigerant flow.

Question 73: Before adding oil to an ammonia compressor, what should the operator check?

That the oil is warm from sitting in the sun
That the oil has been mixed with a little ammonia
That the oil is the type and grade the compressor manufacturer specifies (Correct answer)
That the oil is the cheapest grade available

Correct answer: That the oil is the type and grade the compressor manufacturer specifies

Using the specified oil type and viscosity grade keeps the compressor properly lubricated and avoids compatibility problems.

Question 74: What color code identifies NIOSH air-purifying cartridges for ammonia/methylamine?

Black
Green (Correct answer)
Yellow
Magenta

Correct answer: Green

Ammonia/methylamine cartridges are color-coded green.

Question 75: Which condition most directly increases the compression ratio of a refrigeration compressor?

Lowering condensing pressure
Raising suction pressure while condensing pressure stays the same
Reducing suction superheat
Lowering suction pressure while condensing pressure stays the same (Correct answer)

Correct answer: Lowering suction pressure while condensing pressure stays the same

Compression ratio is absolute discharge pressure divided by absolute suction pressure, so lowering suction pressure raises the ratio.

Question 76: What effect do non-condensable gases such as air have in a refrigeration system?

They improve oil return
They lower head pressure and save energy
They raise condensing pressure and increase power use (Correct answer)
They have no effect

Correct answer: They raise condensing pressure and increase power use

Non-condensables accumulate in the condenser, raising head pressure and compressor energy consumption.

Question 77: What is the IDLH (Immediately Dangerous to Life or Health) concentration for ammonia established by NIOSH?

1,000 ppm
50 ppm
300 ppm (Correct answer)
5,000 ppm

Correct answer: 300 ppm

NIOSH lists 300 ppm as the IDLH concentration for ammonia.

Question 78: Compared to air, ammonia vapor at room temperature is:

Heavier than air only when it is dry
About twice as dense, so it settles to the floor
About 60% as dense, so it tends to rise (Correct answer)
The same density, so it mixes evenly

Correct answer: About 60% as dense, so it tends to rise

Ammonia's molecular weight of about 17 versus air's roughly 29 makes dry ammonia vapor lighter than air.

Question 79: Under CERCLA, what is the reportable quantity (RQ) for an anhydrous ammonia release within a 24-hour period?

1,000 pounds
10 pounds
500 pounds
100 pounds (Correct answer)

Correct answer: 100 pounds

Ammonia has a CERCLA reportable quantity of 100 pounds released within any 24-hour period.

Question 80: A routine oil acid test on a halocarbon compressor comes back positive. What does this most likely indicate?

The oil is new and needs a break-in period
The compressor is short of oil
The suction pressure is too high
Moisture contamination or a motor burnout has produced acids (Correct answer)

Correct answer: Moisture contamination or a motor burnout has produced acids

Acid in the oil typically results from moisture or a motor burnout and requires corrective cleanup.

Question 81: After a compressor motor is replaced, what preventive step helps avoid premature coupling and bearing failure?

Lowering the suction pressure setpoint
Checking shaft alignment with a dial indicator or laser tool (Correct answer)
Running the compressor without a coupling guard
Increasing the oil charge

Correct answer: Checking shaft alignment with a dial indicator or laser tool

Correct alignment reduces vibration and wear on couplings, seals, and bearings.

Question 82: What is the role of an oil separator in an ammonia refrigeration system?

To remove oil from the discharge gas before it enters the condenser (Correct answer)
To separate non-condensable gases from refrigerant
To filter contaminants from the suction line
To separate refrigerant vapor from liquid

Correct answer: To remove oil from the discharge gas before it enters the condenser

An oil separator removes compressor oil from the hot discharge gas and returns it to the compressor crankcase, preventing oil from accumulating in the system and fouling heat exchangers.

Question 83: Which statement about skin contact with liquid ammonia is correct?

It only affects the eyes, not skin
It causes only a mild itch
It is harmless if the skin is dry
It can cause both frostbite and caustic chemical burns (Correct answer)

Correct answer: It can cause both frostbite and caustic chemical burns

Liquid ammonia flashes at -28°F, freezing tissue, while also being strongly alkaline and corrosive.

Question 84: Scale buildup inside the water tubes of a water-cooled condenser will most likely result in what?

Increased subcooling capacity
Lower water pressure drop
Higher condensing pressure (Correct answer)
Lower compressor discharge temperature

Correct answer: Higher condensing pressure

Scale insulates the tubes, reducing heat transfer and forcing the condensing temperature and pressure up.

Question 85: An evaporative condenser rejects most of its heat by which mechanism?

Radiation from the fan motor
Sensible heating of the sump water only
Evaporation of spray water over the coil (Correct answer)
Conduction through the casing to ambient air

Correct answer: Evaporation of spray water over the coil

Evaporating water absorbs large amounts of latent heat from the refrigerant inside the coil.

Question 86: An operator is responding to a small liquid ammonia leak in a machinery room. After ensuring proper ventilation and donning appropriate PPE, what is a critical safety consideration regarding the use of water to address the situation?

A direct, high-pressure water jet should be used to quickly dilute and wash away the spill.
Water fog or spray should be used to knock down ammonia vapors, but a solid stream should not be directed at the liquid pool. (Correct answer)
Water should never be used as it can freeze instantly on contact with liquid ammonia.
Only hot water should be used to prevent a violent boiling reaction with the cold refrigerant.

Correct answer: Water fog or spray should be used to knock down ammonia vapors, but a solid stream should not be directed at the liquid pool.

Using a water fog or spray is an effective method for controlling and knocking down ammonia vapors, which are toxic. However, spraying a solid jet of water directly into a pool of liquid ammonia can cause a violent reaction, rapidly vaporizing the ammonia and creating a larger, more hazardous vapor cloud.

Question 87: Which instrument is used to measure both suction and discharge pressures simultaneously on a refrigeration system?

A manifold gauge set (Correct answer)
A hygrometer
A manometer
A thermometer

Correct answer: A manifold gauge set

A manifold gauge set has two gauges — a low-side (blue) for suction pressure and a high-side (red) for discharge pressure — allowing both readings at the same time.

Question 88: Why is proper ventilation important when working with refrigerants?

To keep tools cool
To avoid gas accumulation (Correct answer)
To increase airflow to compressors
To remove debris

Correct answer: To avoid gas accumulation

Proper ventilation is crucial when working with refrigerants because many are heavier than air and can displace oxygen, leading to asphyxiation in enclosed spaces. Additionally, some refrigerants can be flammable or toxic, and ventilation helps dissipate these gases. This prevents dangerous concentrations from accumulating and ensures a safe breathing environment for workers.

Question 89: When halocarbon refrigerants contact an open flame or hot surface, which toxic products can form?

Ozone and oxygen
Nitrogen and water vapor
Phosgene, hydrogen fluoride, and hydrogen chloride (Correct answer)
Carbon monoxide only

Correct answer: Phosgene, hydrogen fluoride, and hydrogen chloride

Thermal decomposition of halocarbons produces acids like HF and HCl and, for chlorinated refrigerants, phosgene.

Question 90: When draining oil from an ammonia vessel, which practice is safest?

Open the drain valve fully to finish quickly
Use a self-closing (spring-loaded) drain valve with a second isolation valve, and never leave it unattended (Correct answer)
Remove the drain valve cap while the system is running
Drain while the vessel is at full discharge pressure

Correct answer: Use a self-closing (spring-loaded) drain valve with a second isolation valve, and never leave it unattended

A spring-loaded valve shuts if released, and constant attendance keeps an ammonia release from going unnoticed.

Question 91: When adding oil to an operating ammonia compressor, why must the oil be the type specified by the manufacturer?

Any oil works because ammonia is not miscible
Oil type only affects the oil separator
Incorrect oil can have improper viscosity or compatibility, causing poor lubrication, carbon, or sludge (Correct answer)
Only the color of the oil matters

Correct answer: Incorrect oil can have improper viscosity or compatibility, causing poor lubrication, carbon, or sludge

Using the wrong oil can cause poor lubrication, varnish, or incompatibility with the refrigerant, damaging the compressor.

Question 92: What is the primary purpose of a high-pressure cutout switch in a refrigeration system?

To control condenser fan speed
To increase system efficiency
To shut down the compressor when discharge pressure exceeds a safe limit (Correct answer)
To regulate suction pressure

Correct answer: To shut down the compressor when discharge pressure exceeds a safe limit

A high-pressure cutout switch protects the compressor and system by automatically shutting down the compressor when discharge pressure rises above a preset safe limit.

Question 93: What is the purpose of a head pressure control valve in cold weather operation?

To increase compressor discharge temperature
To maintain sufficient condensing pressure so the expansion device operates correctly during cold weather (Correct answer)
To bypass refrigerant around the evaporator
To reduce suction pressure during low ambient conditions

Correct answer: To maintain sufficient condensing pressure so the expansion device operates correctly during cold weather

Head pressure control valves ensure condensing pressure does not drop too low in cold ambient conditions, which would starve the expansion valve of adequate liquid pressure.

Question 94: An operator hears a sharp knocking sound from a reciprocating compressor that worsens when the suction line ices up. What should be done first?

Add oil to the crankcase immediately
Increase compressor speed to clear the liquid
Open the discharge bypass to the high side
Throttle or close the suction stop valve and reduce feed to the evaporator to stop liquid carryover (Correct answer)

Correct answer: Throttle or close the suction stop valve and reduce feed to the evaporator to stop liquid carryover

Knocking with frosted suction indicates liquid slugging, so the operator should throttle suction and correct the liquid feed to protect the compressor.

Question 95: What type of valve is recommended on oil drain connections so flow stops if the operator lets go?

Spring-loaded self-closing (quick-closing) valve (Correct answer)
Gate valve
Check valve
Globe valve

Correct answer: Spring-loaded self-closing (quick-closing) valve

A spring-loaded self-closing valve automatically shuts if the operator releases it during oil draining.

Question 96: What is the function of an oil drain valve on an ammonia refrigeration vessel?

To release refrigerant pressure before maintenance
To drain accumulated oil from the vessel back to the oil pot or drain point (Correct answer)
To equalize pressure between the vessel and atmosphere
To sample refrigerant quality for purity testing

Correct answer: To drain accumulated oil from the vessel back to the oil pot or drain point

Oil drain valves allow accumulated compressor oil, which is denser than ammonia and settles at the bottom, to be drained from vessels and returned to the oil management system.

Question 97: Under ANSI/IIAR guidance, how often should pressure relief valves on ammonia systems typically be replaced?

Every 20 years
Every 5 years (Correct answer)
Never, if they pass visual inspection
Only after they discharge

Correct answer: Every 5 years

IIAR recommends replacing relief valves every five years because internal corrosion and debris can prevent proper operation.

Question 98: What makes ammonia's refrigerating effect per pound so large compared with halocarbons?

Its low critical temperature
Its very high latent heat of vaporization (Correct answer)
Its high molecular weight
Its low specific heat

Correct answer: Its very high latent heat of vaporization

Ammonia's latent heat of vaporization is several times that of common halocarbons, so less mass flow is needed.

Question 99: How does an automatic refrigerated purger separate air from ammonia?

It filters the air out through a membrane
It heats the mixture so the air condenses
It cools the mixture so the ammonia condenses and the air is left to vent (Correct answer)
It spins the mixture in a centrifuge

Correct answer: It cools the mixture so the ammonia condenses and the air is left to vent

A purger chills the sampled gas below the condensing temperature, so ammonia condenses and returns while the noncondensables collect and are vented.

Question 100: In an industrial ammonia system, what is the purpose of a purger or non-condensable gas purger?

To purge oil from the system
To remove air and other non-condensable gases that accumulate in the high side and reduce system efficiency (Correct answer)
To remove moisture from the refrigerant
To vent excess refrigerant charge

Correct answer: To remove air and other non-condensable gases that accumulate in the high side and reduce system efficiency

Non-condensable gases such as air raise the condensing pressure, reduce efficiency, and can create hazardous conditions; a purger automatically vents them from the high side.

Question 101: What does liquid slugging in an ammonia compressor sound like and what damage can it cause?

A high-pitched whistle; causes refrigerant loss
A quiet humming; reduces oil pressure
A loud knocking or hammering sound; can break valve reeds, connecting rods, or cause catastrophic compressor failure (Correct answer)
A hissing sound; causes refrigerant overcharge

Correct answer: A loud knocking or hammering sound; can break valve reeds, connecting rods, or cause catastrophic compressor failure

Liquid slugging sounds like heavy knocking or hammering because liquid is incompressible; it can shatter valve plates, bend or break connecting rods, and cause catastrophic compressor failure.

Question 102: Which type of fire extinguisher is suitable for electrical fires in refrigeration areas?

Class B
Class D
Class A
Class C (Correct answer)

Correct answer: Class C

Class C fire extinguishers are specifically designed for electrical fires, which are common in refrigeration areas due to motors, wiring, and control panels. These extinguishers use non-conductive agents like carbon dioxide or dry chemicals. This prevents the risk of electrical shock to the user and effectively suppresses fires involving energized electrical equipment.

Question 103: What is the purpose of an oil filter differential pressure reading on a compressor?

It shows how full the oil separator is
It measures noncondensable gas levels
It shows the refrigerant charge
It shows when the filter is getting clogged and needs to be changed (Correct answer)

Correct answer: It shows when the filter is getting clogged and needs to be changed

Pressure drop across the filter rises as it loads with debris, telling the operator when to change it.

Question 104: An emergency eyewash station meeting ANSI Z358.1 must deliver flushing fluid for at least how long?

30 minutes
2 minutes
15 minutes (Correct answer)
5 minutes

Correct answer: 15 minutes

ANSI Z358.1 requires eyewash units to provide a continuous flush for at least 15 minutes.

Question 105: Because anhydrous ammonia vapor is lighter than air, where would a leak typically accumulate in an enclosed machinery room?

Evenly at mid-height only
Near the ceiling (Correct answer)
In floor drains and pits
Near the floor

Correct answer: Near the ceiling

Ammonia vapor has a density of about 0.6 relative to air, so it rises toward the ceiling.

Question 106: What is the typical alarm set point at which machinery room ammonia detectors activate an alarm and emergency ventilation?

10,000 ppm
5 ppm
300 ppm
25 ppm (Correct answer)

Correct answer: 25 ppm

IIAR 2 requires detection at 25 ppm to activate alarms and machinery room ventilation.

Question 107: In a standard vapor-compression refrigeration cycle, what is the primary function of the compressor?

To reduce the pressure of the liquid refrigerant before the evaporator.
To cool the refrigerant into a high-pressure liquid.
To raise the pressure and temperature of the refrigerant vapor. (Correct answer)
To absorb heat from the space being cooled.

Correct answer: To raise the pressure and temperature of the refrigerant vapor.

The compressor takes low-pressure, low-temperature refrigerant vapor from the evaporator and compresses it into a high-pressure, high-temperature vapor. This process is necessary to raise the refrigerant's temperature above the temperature of the condensing medium (like ambient air or water), allowing it to release heat in the condenser.

Question 108: What type of control is used to cycle a refrigeration compressor on and off based on box or space temperature?

Float switch
Thermostat (Correct answer)
Flow switch
Pressure differential switch

Correct answer: Thermostat

A thermostat cycles the compressor or refrigerant solenoid valve on and off in response to the temperature of the refrigerated space, maintaining the desired setpoint.

Question 109: In a two-stage ammonia system, the low-stage (booster) compressor discharges into:

The condenser directly
The high-pressure receiver
The evaporator
The intermediate-pressure intercooler or vessel (Correct answer)

Correct answer: The intermediate-pressure intercooler or vessel

The booster raises gas to intermediate pressure, where the intercooler desuperheats it before the high-stage compressor takes it.

Question 110: Off-cycle (air) defrost is practical only when the refrigerated space is at what condition?

At any temperature if fans run in reverse
Exactly at the evaporator saturation temperature
Above freezing, around 34°F or warmer (Correct answer)
Below 0°F

Correct answer: Above freezing, around 34°F or warmer

Off-cycle defrost relies on room air to melt frost, which only works when the room is above 32°F.

RETA Certified Assistant Refrigeration Operator (CARO)

The CARO is an entry-level RETA certification exam assessing whether an operator has the basic knowledge to safely function in an ammonia refrigeration engine room under the supervision of a more experienced operator. It covers refrigeration fundamentals, compressor operation and maintenance, refrigerant properties, and safety.

110

Questions

180 min

Time Limit

70%

To Pass

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