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

Question 1: A pressure relief valve on a refrigeration vessel is required to discharge to:

The condenser inlet
A safe outdoor location or treatment system per code (Correct answer)
The evaporator pan
The compressor suction line

Correct answer: A safe outdoor location or treatment system per code

Pressure relief valves must discharge to a safe outdoor location or an approved treatment/containment system to protect personnel and comply with codes such as IIAR and ASHRAE 15.

Question 2: In an evaporative condenser, how is heat primarily rejected from the refrigerant?

By evaporation of water sprayed over the coil while air is drawn through (Correct answer)
By water flowing through tubes inside a shell
By direct contact between refrigerant and spray water
By air passing over dry finned coils only

Correct answer: By evaporation of water sprayed over the coil while air is drawn through

Evaporative condensers reject heat mainly through the latent heat of water evaporating off the coil surface.

Question 3: 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 4: What is the OSHA permissible exposure limit (PEL) for ammonia as an 8-hour time-weighted average?

100 ppm
50 ppm (Correct answer)
35 ppm
25 ppm

Correct answer: 50 ppm

OSHA 29 CFR 1910.1000 sets the ammonia PEL at 50 ppm TWA.

Question 5: Under EPA Section 608 of the Clean Air Act, what is prohibited for halocarbon refrigerants such as R-22 and R-404A?

Recycling refrigerant on site
Knowingly venting refrigerant to the atmosphere during service (Correct answer)
Leak testing with nitrogen
Recovering refrigerant into DOT cylinders

Correct answer: Knowingly venting refrigerant to the atmosphere during service

Section 608 prohibits knowingly venting ozone-depleting and substitute refrigerants during maintenance, service, repair or disposal.

Question 6: Under CERCLA, what is the reportable quantity (RQ) for an anhydrous ammonia release within a 24-hour period?

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

Correct answer: 100 pounds

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

Question 7: What does a check valve do in a refrigeration piping system?

Regulates pressure by venting refrigerant to atmosphere
Prevents refrigerant from flowing backward in the piping (Correct answer)
Balances pressure between high and low sides
Controls superheat at the evaporator outlet

Correct answer: Prevents refrigerant from flowing backward in the piping

A check valve allows refrigerant to flow in only one direction, preventing reverse flow that could damage compressors or disrupt system operation.

Question 8: Why must an evaporator be pumped out before hot gas is introduced for defrost?

To avoid hydraulic shock from hot gas hitting liquid refrigerant (Correct answer)
To drain oil into the receiver
To raise the room temperature
To allow the fans to keep running

Correct answer: To avoid hydraulic shock from hot gas hitting liquid refrigerant

Hot gas entering a coil full of cold liquid can collapse vapor and cause dangerous liquid hammer.

Question 9: What makes ammonia's refrigerating effect per pound so large compared with halocarbons?

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

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 10: An operator at a cold storage facility notices violent foaming in the compressor's oil sight glass immediately upon startup. This phenomenon quickly subsides. What is the most likely cause of this event?

A malfunctioning high-pressure cut-out switch.
Refrigerant migration into the crankcase during the off-cycle. (Correct answer)
Excessive superheat at the compressor suction.
Non-condensables present in the refrigeration system.

Correct answer: Refrigerant migration into the crankcase during the off-cycle.

This condition is a classic sign of a 'flooded start.' During the off-cycle, refrigerant can migrate to the coldest part of the system, which is often the compressor crankcase. There, it condenses and mixes with the oil. Upon startup, the sudden drop in crankcase pressure causes the liquid refrigerant to boil violently, creating foam.

Question 11: 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
Incorrect oil can have improper viscosity or compatibility, causing poor lubrication, carbon, or sludge (Correct answer)
Only the color of the oil matters
Oil type only affects the oil separator

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 12: What is the purpose of the oil filter differential pressure reading on a screw compressor?

To measure refrigerant flow rate
To show oil temperature rise across the cooler
To set the slide valve position
To indicate when the filter is clogged and needs replacement (Correct answer)

Correct answer: To indicate when the filter is clogged and needs replacement

A rising pressure drop across the oil filter shows the element is loading with contaminants and should be changed.

Question 13: In a halocarbon system, a moisture-indicating sight glass shows yellow instead of green. What should the operator conclude?

The system has too much refrigerant
The refrigerant is dry and in good condition
Moisture is present and the drier may need changing (Correct answer)
The sight glass needs to be cleaned

Correct answer: Moisture is present and the drier may need changing

On most indicators, yellow (or pink) means wet while green (or blue) means dry.

Question 14: What is the primary purpose of a high-pressure cutout switch in a refrigeration system?

To increase system efficiency
To control condenser fan speed
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 15: Which valve is recommended on the final drain point of an ammonia oil drain?

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

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

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

Correct answer: 15 minutes

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

Question 17: Why might a reciprocating compressor crankcase heater be used during the off cycle?

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

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 18: When troubleshooting an ammonia system that is not reaching its design suction temperature, what should be checked first?

Refrigerant charge level and expansion device operation (Correct answer)
Compressor oil level
Condenser water temperature
Electrical phase balance

Correct answer: Refrigerant charge level and expansion device operation

Insufficient refrigerant charge or a malfunctioning expansion device are the most common reasons a system cannot reach its design suction temperature, making these the first things to check.

Question 19: The purpose of using unloaders on a multi-cylinder reciprocating compressor is to:

Reduce the starting torque and provide capacity control. (Correct answer)
Increase the compression ratio during high load.
Ensure proper oil return to the crankcase.
Prevent oil from leaving the compressor.

Correct answer: Reduce the starting torque and provide capacity control.

Unloaders work by holding the suction valves open on one or more cylinders. This prevents those cylinders from compressing gas, which significantly reduces the load on the motor during startup. It also serves as a method of capacity control by effectively reducing the compressor's pumping volume to match lower cooling demands.

Question 20: In an ammonia system, where does lubricating oil tend to collect, requiring periodic draining?

Inside the expansion valve
In the discharge line near the compressor outlet
At the top of the condenser
In low points of the low side, such as oil pots and vessel bottoms (Correct answer)

Correct answer: In low points of the low side, such as oil pots and vessel bottoms

Oil is heavier than and largely immiscible with liquid ammonia, so it settles at low points.

Question 21: Subcooling is best described as:

Lowering suction pressure to reduce temperature
Liquid cooled below its saturation temperature at the same pressure (Correct answer)
Vapor heated above saturation
Removing oil from the evaporator

Correct answer: Liquid cooled below its saturation temperature at the same pressure

Subcooling is the number of degrees liquid refrigerant is below its condensing (saturation) temperature.

Question 22: In an ammonia refrigeration system, where does carried-over compressor oil tend to collect?

Evenly mixed throughout the liquid ammonia
At low points of vessels and evaporators, below the liquid ammonia (Correct answer)
In the discharge line near the compressor
At the top of the condenser

Correct answer: At low points of vessels and evaporators, below the liquid ammonia

Mineral oil is denser than liquid ammonia and does not mix with it, so it settles at the low points of vessels and coils.

Question 23: 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 maintain refrigerant charge
To regulate discharge temperature
To monitor refrigerant purity

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 24: A dirty evaporator coil with restricted airflow will most likely cause which condition?

Higher suction pressure and higher capacity
Lower head pressure only
Higher room humidity with no effect on pressures
Lower suction pressure and reduced capacity (Correct answer)

Correct answer: Lower suction pressure and reduced capacity

Less airflow means less heat absorbed, which lowers evaporating pressure and capacity.

Question 25: Why is it important to remove noncondensable gases from a refrigeration system?

They raise head pressure, which wastes compressor energy and lowers capacity (Correct answer)
They make the oil too thin
They cause the evaporator to freeze solid
They lower discharge temperatures too much

Correct answer: They raise head pressure, which wastes compressor energy and lowers capacity

Higher condensing pressure makes the compressor work harder, so it uses more power and moves less refrigeration.

Question 26: When an ammonia purger vents noncondensables, the vented gas is usually routed through what before release?

Into a water bubbler or water tank that absorbs any ammonia (Correct answer)
Into the compressor suction line
Directly into the machine room air
Into the oil pot

Correct answer: Into a water bubbler or water tank that absorbs any ammonia

Ammonia is very soluble in water, so passing the purge gas through water captures ammonia that comes along with the air.

Question 27: In a typical shell-and-tube water-cooled ammonia condenser, where does the refrigerant flow?

Through the cooling tower fill
In the shell, around the tubes (Correct answer)
Inside the water box
Inside the tubes, with water in the shell

Correct answer: In the shell, around the tubes

Cooling water runs through the cleanable tubes while ammonia vapor condenses on the shell side.

Question 28: How should refrigerant cylinders be stored to maintain compliance?

In locked containers underground
In upright position with proper labels (Correct answer)
Near heat sources for easy use
Lying on their side

Correct answer: In upright position with proper labels

Refrigerant cylinders should always be stored in an upright position and secured to prevent tipping, with proper labels clearly indicating their contents. This storage method ensures safety, prevents damage to the valve, and allows for easy identification of the refrigerant type. Proper storage is crucial for safe handling and regulatory compliance.

Question 29: Before an operator works on a compressor motor, which OSHA standard governs isolating its energy sources?

29 CFR 1910.134 Respiratory Protection
29 CFR 1910.1200 Hazard Communication
29 CFR 1910.147 Control of Hazardous Energy (Correct answer)
29 CFR 1910.146 Confined Spaces

Correct answer: 29 CFR 1910.147 Control of Hazardous Energy

Lockout/tagout is governed by 29 CFR 1910.147, the control of hazardous energy standard.

Question 30: 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 31: When halocarbon refrigerants contact an open flame or hot surface, which toxic products can form?

Ozone and oxygen
Phosgene, hydrogen fluoride, and hydrogen chloride (Correct answer)
Nitrogen and water vapor
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 32: In cold weather, how is condensing pressure on an evaporative condenser commonly kept from falling too low?

By increasing bleed-off
By adding more spray water
By cycling fans or reducing fan speed (Correct answer)
By opening the purger

Correct answer: By cycling fans or reducing fan speed

Reducing airflow lowers heat rejection, holding head pressure up for proper system operation.

Question 33: A room requiring a warmer evaporator temperature than the common suction main is controlled by which device at the evaporator outlet?

Relief valve
Back-pressure (evaporator pressure) regulator (Correct answer)
High-pressure float
Thermal expansion valve

Correct answer: Back-pressure (evaporator pressure) regulator

A back-pressure regulator holds the evaporator at a higher pressure, and therefore temperature, than the suction main.

Question 34: What is the main job of the oil separator in an ammonia compressor discharge line?

To separate oil from the discharge gas and return it to the compressor (Correct answer)
To filter moisture out of the ammonia
To cool the discharge gas before it enters the condenser
To remove noncondensable gases from the refrigerant

Correct answer: To separate oil from the discharge gas and return it to the compressor

The oil separator captures oil carried out of the compressor with the hot gas and returns it to the crankcase or oil system.

Question 35: How can vibration in a refrigeration system be reduced during preventive maintenance?

Turn off ventilation
Tighten mounting and connections (Correct answer)
Loosen electrical wiring
Remove insulation

Correct answer: Tighten mounting and connections

Vibration in a refrigeration system can indicate loose components, which can lead to increased noise, wear, and potential equipment failure. During preventive maintenance, tightening mounting bolts, brackets, and connections helps secure components. This action reduces excessive vibration and ensures the system operates smoothly and reliably, preventing premature damage.

Question 36: What is the approximate critical temperature of carbon dioxide (R-744)?

32°F
87.8°F (Correct answer)
-69.8°F
271°F

Correct answer: 87.8°F

CO2's critical point is about 87.8°F (31°C), so systems often operate transcritically in warm conditions.

Question 37: Heat that changes a substance's temperature without changing its state is called what?

Specific heat ratio
Latent heat
Sensible heat (Correct answer)
Heat of compression

Correct answer: Sensible heat

Sensible heat can be measured with a thermometer because it changes temperature.

Question 38: A routine oil acid test on a halocarbon compressor comes back positive. What does this most likely indicate?

The compressor is short of oil
The oil is new and needs a break-in period
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 39: On a reciprocating compressor, what does a 'net oil pressure' reading represent?

Oil pump discharge pressure minus condensing pressure
Oil pump discharge pressure minus crankcase (suction) pressure (Correct answer)
Total oil pump discharge pressure alone
Crankcase pressure minus atmospheric pressure

Correct answer: Oil pump discharge pressure minus crankcase (suction) pressure

Net oil pressure is pump discharge pressure minus crankcase pressure, the true pressure available to lubricate bearings.

Question 40: Heavy frost accumulation on an air-cooling evaporator coil typically causes which condition?

Higher condenser water temperature
Increased evaporator capacity
Reduced airflow and a falling suction pressure (Correct answer)
Rising room humidity and rising suction pressure

Correct answer: Reduced airflow and a falling suction pressure

Frost insulates the coil and blocks airflow, so less heat is absorbed and suction pressure drops.

Question 41: After a hot gas defrost, why are evaporator fans normally delayed before restarting?

To let the condenser cool down
To allow oil to return to the compressor
To refreeze remaining water droplets on the coil before air movement (Correct answer)
To prevent the liquid pump from cavitating

Correct answer: To refreeze remaining water droplets on the coil before air movement

The fan delay lets water on the coil refreeze so it is not blown into the room or onto the product.

Question 42: Very low or zero superheat at the compressor suction most likely indicates what risk?

Oil logging in the receiver
Liquid floodback that can slug the compressor (Correct answer)
High discharge temperature from a starved evaporator
Noncondensable gases in the condenser

Correct answer: Liquid floodback that can slug the compressor

Zero superheat means liquid may be reaching the compressor, which can damage valves and bearings.

Question 43: What health hazard makes water treatment and cleaning of evaporative condensers especially important?

Ammonia dissolving into the water
Ozone generation
Carbon monoxide buildup
Legionella bacteria growth (Correct answer)

Correct answer: Legionella bacteria growth

Warm recirculating water can breed Legionella, which spreads through drift and causes Legionnaires' disease.

Question 44: What is the purpose of a log book or equipment log in a refrigeration machine room?

To record operating conditions, maintenance performed, refrigerant added, and alarms — providing a baseline for troubleshooting and regulatory compliance (Correct answer)
To track employee schedules
To store equipment purchase receipts
To document utility costs only

Correct answer: To record operating conditions, maintenance performed, refrigerant added, and alarms — providing a baseline for troubleshooting and regulatory compliance

Equipment logs record operating data, maintenance history, refrigerant additions, and incidents, creating a baseline that helps operators identify trends, diagnose problems, and demonstrate regulatory compliance.

Question 45: What does a solenoid valve do in a refrigeration control circuit?

Controls refrigerant flow by opening or closing electrically (Correct answer)
Measures refrigerant temperature
Regulates compressor speed
Monitors oil pressure

Correct answer: Controls refrigerant flow by opening or closing electrically

A solenoid valve is an electrically operated valve that opens or closes to control the flow of refrigerant in response to an electrical signal from the control system.

Question 46: When manually purging non-condensable gases from an ammonia system, an operator connects a hose from a purge valve on the high-pressure receiver to a bucket of water. What is the visual indicator that mostly non-condensable gas, rather than ammonia, is being vented?

The water in the bucket begins to freeze rapidly.
The water turns a milky white color.
The water level in the bucket rises quickly.
A continuous stream of bubbles rises to the surface of the water. (Correct answer)

Correct answer: A continuous stream of bubbles rises to the surface of the water.

Ammonia has a very high affinity for water and will be readily absorbed with a crackling sound. Non-condensable gases like air and nitrogen are not soluble in water. Therefore, when these gases are bubbled through the water, they will rise to the surface and escape to the atmosphere. A steady stream of bubbles indicates the removal of non-condensables. The purging should be stopped once the bubbling ceases, indicating that mostly ammonia is now flowing.

Question 47: Excessive vibration in a reciprocating ammonia compressor is best diagnosed using which method?

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

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 48: An operator observes that the refrigerant entering the expansion valve is not a solid column of liquid. Which of the following conditions is the most likely cause and consequence?

High superheat, which will improve system efficiency.
Normal operation, as some vapor is expected at this point.
Low subcooling, which can cause the refrigerant to 'flash' prematurely, reducing efficiency. (Correct answer)
Excessive subcooling, which will cause the compressor to work harder.

Correct answer: Low subcooling, which can cause the refrigerant to 'flash' prematurely, reducing efficiency.

Subcooling is the process of cooling the liquid refrigerant below its saturation temperature after it has fully condensed. A proper amount of subcooling ensures that a solid stream of liquid refrigerant reaches the expansion valve. If subcooling is too low, some of the liquid may vaporize (flash) before the valve due to pressure drops in the liquid line. This reduces the refrigerating effect in the evaporator and lowers overall system efficiency.

Question 49: When calibrating a pressure gauge on an ammonia system, what safety precaution must be taken?

The gauge must be isolated, pressure relieved, and proper PPE worn before disconnecting (Correct answer)
The refrigerant must be vented to atmosphere before gauge removal
Calibration must be done while the compressor is running
The system must be fully charged before calibration

Correct answer: The gauge must be isolated, pressure relieved, and proper PPE worn before disconnecting

Before removing or calibrating a gauge on an ammonia system, the gauge valve must be isolated, pressure bled off safely, and full ammonia PPE including respirator and gloves must be worn.

Question 50: In an ammonia refrigeration system, a 'king valve' is located:

On the discharge of the cooling tower pump
At the inlet of the evaporative condenser
At the outlet of the high-pressure receiver on the liquid line (Correct answer)
At the inlet of the compressor suction line

Correct answer: At the outlet of the high-pressure receiver on the liquid line

The king valve is the main liquid shutoff valve located at the outlet of the high-pressure receiver, allowing the system liquid charge to be isolated in the receiver for service or pump-down operations.

Question 51: What is the main reason for checking coupling alignment between a compressor and its motor?

To increase refrigerant flow
To adjust the slide valve position
To raise oil pressure
To prevent vibration, bearing wear, and seal failure (Correct answer)

Correct answer: To prevent vibration, bearing wear, and seal failure

Misalignment causes vibration and side loads that wear bearings, couplings, and shaft seals prematurely.

Question 52: After a compressor motor is replaced, what preventive step helps avoid premature coupling and bearing failure?

Running the compressor without a coupling guard
Lowering the suction pressure setpoint
Checking shaft alignment with a dial indicator or laser tool (Correct answer)
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 53: What does a pressure-temperature (PT) chart help a refrigeration operator determine?

Compressor amperage draw
Evaporator airflow velocity
The saturation temperature corresponding to a measured refrigerant pressure (Correct answer)
Oil viscosity at operating temperature

Correct answer: The saturation temperature corresponding to a measured refrigerant pressure

A PT chart lists the corresponding saturation temperature for each pressure of a given refrigerant, allowing operators to determine if the system is operating at the correct conditions.

Question 54: At atmospheric pressure, approximately what is the boiling point of ammonia (R-717)?

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

Correct answer: -28°F

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

Question 55: What is the state and pressure of the refrigerant as it leaves the condenser and before it enters the metering device?

Low-pressure, cold vapor
High-pressure, high-temperature vapor
High-pressure, warm liquid (Correct answer)
Low-pressure, low-temperature liquid

Correct answer: High-pressure, warm liquid

In the condenser, the high-pressure, high-temperature vapor from the compressor rejects heat to the surroundings and condenses into a liquid. Therefore, the refrigerant leaving the condenser is a high-pressure, warm (medium temperature) liquid, ready to be sent to the metering device.

Question 56: Non-condensable gases trapped in a condenser most directly cause which problem?

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

Correct answer: Abnormally high head pressure

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

Question 57: In an ammonia system, what is the primary function of the high-pressure receiver?

Separate oil from discharge gas
Cool the discharge gas before it reaches the condenser
Remove non-condensable gases from the condenser
Store liquid refrigerant and absorb fluctuations in system charge (Correct answer)

Correct answer: Store liquid refrigerant and absorb fluctuations in system charge

The high-pressure receiver stores condensed liquid and buffers charge changes as load varies.

Question 58: In the event of a major, uncontrolled outdoor ammonia release, which of the following is the most important factor for determining a safe personnel evacuation route?

The time of day.
The location of the plant's main office.
The location of the nearest emergency exit.
The current wind direction. (Correct answer)

Correct answer: The current wind direction.

Ammonia vapor is carried by the wind. To evacuate safely, personnel must move upwind and crosswind to avoid the traveling plume of hazardous gas. Windsocks are often required at facilities for this reason. The other factors are secondary to avoiding the ammonia cloud itself.

Question 59: 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 floor
In floor drains and pits
Near the ceiling (Correct answer)

Correct answer: Near the ceiling

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

Question 60: What is the danger of liquid slugging in a refrigerant piping system?

Liquid refrigerant entering the compressor cylinders can cause catastrophic mechanical failure (Correct answer)
Liquid refrigerant in the discharge line raises compressor head pressure excessively
Liquid accumulation in suction lines increases refrigerant velocity above safe limits
Liquid slugs cause check valves to chatter and wear out prematurely

Correct answer: Liquid refrigerant entering the compressor cylinders can cause catastrophic mechanical failure

Liquid refrigerant is incompressible, so if it enters a reciprocating compressor cylinder it can hydraulically fracture valve plates, break connecting rods, or destroy the compressor.

Question 61: Compared to air, ammonia vapor at room temperature is:

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

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 62: For RMP Program 2 and 3 processes, how often must compliance audits be conducted?

Every 3 years (Correct answer)
Every year
Every 5 years
Only after an incident

Correct answer: Every 3 years

RMP compliance audits must be conducted at least every three years.

Question 63: What is a common sign that noncondensable gases are in a refrigeration system?

Lower-than-normal head pressure
Frost forming on the discharge line
Higher-than-normal head pressure for the condensing temperature (Correct answer)
Lower compressor amperage

Correct answer: Higher-than-normal head pressure for the condensing temperature

Noncondensables add their own partial pressure, so condenser pressure goes above the saturation pressure for the actual condensing temperature.

Question 64: In an industrial ammonia refrigeration system, what is the primary purpose of an automatic purger connected to the high side of the system?

To remove non-condensable gases like air and hydrogen. (Correct answer)
To drain excess lubricating oil from the condenser.
To vent off high-pressure liquid refrigerant during an over-pressure event.
To remove refrigerant that has broken down over time.

Correct answer: To remove non-condensable gases like air and hydrogen.

Non-condensable gases, such as air that may have entered the system during maintenance or hydrogen from the breakdown of ammonia, accumulate in the condenser. These gases do not condense at the same temperature and pressure as the refrigerant, which increases the overall head pressure, reduces system efficiency, and increases energy consumption. An automatic purger is designed to safely and efficiently remove these non-condensable gases. [3, 15, 18]

Question 65: What type of valve is recommended on oil drain connections so flow stops if the operator lets go?

Globe valve
Check valve
Spring-loaded self-closing (quick-closing) valve (Correct answer)
Gate 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 66: An operator needs to perform maintenance that requires opening up a compressor to the atmosphere. What is the critical first step in the pump-down procedure before any components are loosened?

Close the suction and discharge service valves.
Disconnect the main power supply using lockout/tagout procedures.
Slowly throttle the suction stop valve to lower crankcase pressure. (Correct answer)
Attach a gauge manifold to the service ports.

Correct answer: Slowly throttle the suction stop valve to lower crankcase pressure.

Before isolating the compressor, it's crucial to run it and slowly close the suction stop valve. This process, known as pumping down the compressor, safely removes most of the refrigerant from the crankcase. Doing this slowly prevents oil from foaming violently and being carried out of the compressor, which can happen if the pressure is dropped too quickly.

Question 67: An operator observes a steady increase in the condenser approach temperature. Which of the following is the MOST likely cause?

Fouling or scale buildup on the condenser's heat transfer surfaces. (Correct answer)
A significant drop in the ambient wet-bulb temperature.
Excessive subcooling of the liquid refrigerant leaving the condenser.
The system has a low refrigerant charge.

Correct answer: Fouling or scale buildup on the condenser's heat transfer surfaces.

The condenser approach temperature is the difference between the refrigerant's condensing temperature and the temperature of the cooling medium (water or air) leaving the condenser. Fouling, such as mineral scale or algae, acts as an insulator on the heat transfer surfaces, reducing the condenser's efficiency. To reject the same amount of heat, the condensing temperature must rise, which increases the approach temperature. [11, 29]

Question 68: What is the IDLH (Immediately Dangerous to Life or Health) concentration for ammonia established by NIOSH?

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

Correct answer: 300 ppm

NIOSH lists 300 ppm as the IDLH concentration for ammonia.

Question 69: What is the main purpose of applying a water fog or spray to an ammonia vapor cloud?

To ignite and burn off the vapor
To dilute the oil in the system
To absorb and knock down vapor, since ammonia is highly water-soluble (Correct answer)
To cool the compressors

Correct answer: To absorb and knock down vapor, since ammonia is highly water-soluble

Ammonia readily dissolves in water, so a fog pattern helps absorb vapor and control its spread.

Question 70: Which instrument is used to measure both suction and discharge pressures simultaneously on a refrigeration system?

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

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

EPA (Correct answer)
NFPA
OSHA
DOT

Correct answer: EPA

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

Question 72: EPCRA Section 304 requires that a reportable ammonia release also be reported to which agencies?

The State Emergency Response Commission and Local Emergency Planning Committee (Correct answer)
The facility's insurance carrier
The EPA regional administrator only
The local fire marshal only

Correct answer: The State Emergency Response Commission and Local Emergency Planning Committee

EPCRA Section 304 requires notifying the SERC and LEPC for affected areas in addition to federal reporting.

Question 73: An operator at a plant with an evaporative condenser notices that the discharge (head) pressure is significantly higher than normal on a mild day. The water spray nozzles are working correctly and the sump water level is normal. What is the MOST appropriate next check?

Check for a low refrigerant charge in the system.
Ensure the compressor's oil level is correct.
Verify that the condenser fans are operating correctly and airflow is not obstructed. (Correct answer)
Check the superheat at the evaporator outlet.

Correct answer: Verify that the condenser fans are operating correctly and airflow is not obstructed.

An evaporative condenser uses both air and the evaporation of water to reject heat. If the water side appears to be functioning, the next logical step is to check the air side. If the fans are not running, running in reverse, or if airflow is blocked by debris (like leaves or dirt), the condenser's ability to reject heat will be severely limited, causing a rise in discharge pressure. [7, 8, 14]

Question 74: What is a common way to minimize ammonia emissions when removing ammonia from a component before maintenance?

Open the component and let it evaporate
Vent it directly to the atmosphere through the roof
Blow it out with compressed air
Pump it out or transfer it to another part of the system before opening (Correct answer)

Correct answer: Pump it out or transfer it to another part of the system before opening

Pumping down or transferring ammonia to another part of the system before opening keeps releases to a minimum.

Question 75: Water contamination in an ammonia system can cause what problem?

Higher compressor capacity
Removal of noncondensables
Lower evaporator pressure for the same temperature, reducing efficiency (Correct answer)
Better oil separation

Correct answer: Lower evaporator pressure for the same temperature, reducing efficiency

Water mixed with ammonia raises its boiling point, so a lower suction pressure is needed for the same temperature, which reduces efficiency.

Question 76: Moisture contamination in a refrigeration system most commonly causes what problem in the expansion device?

Compressor valve erosion
Higher suction pressure
Increased refrigerant flow
Ice formation that blocks or partially freezes the expansion valve orifice (Correct answer)

Correct answer: Ice formation that blocks or partially freezes the expansion valve orifice

Moisture in the refrigerant freezes at the expansion device orifice where temperature and pressure drop sharply, causing intermittent or permanent blockage and starving the evaporator.

Question 77: A thermostatic expansion valve (TXV) is designed to maintain a constant what?

Evaporator superheat (Correct answer)
Discharge pressure
Condenser subcooling
Evaporator temperature regardless of load

Correct answer: Evaporator superheat

The TXV modulates refrigerant feed to hold a set superheat at the evaporator outlet.

Question 78: 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 oil pressure safety setpoint
The pressure at which the compressor restarts after a low-pressure shutdown (Correct answer)
The discharge pressure limit
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 79: Under ASHRAE Standard 34, what safety classification is assigned to ammonia (R-717)?

B2L (Correct answer)
A2L
A1
B1

Correct answer: B2L

Ammonia has higher toxicity (B) and lower flammability with a slow burning velocity (2L), so it is classified B2L.

Question 80: A compressor has a suction pressure of 15 psig and a discharge pressure of 165 psig at sea level. What is the approximate compression ratio?

8.2
6.0 (Correct answer)
4.7
11.0

Correct answer: 6.0

Using absolute pressures, (165 + 14.7) ÷ (15 + 14.7) = 179.7 ÷ 29.7 ≈ 6.0.

Question 81: 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 Global Warming Potential (GWP)
High latent heat of vaporization (Correct answer)
High miscibility with mineral oil

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

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 83: What is the approximate flammable range of ammonia in air by volume?

1% to 7%
15% to 28% (Correct answer)
30% to 50%
4% to 75%

Correct answer: 15% to 28%

Ammonia is flammable only at fairly high concentrations, roughly 15% to 28% by volume in air.

Question 84: If liquid backs up in a condenser because the drain to the receiver is restricted, what happens?

Head pressure rises because effective condensing surface is lost (Correct answer)
Subcooling disappears completely
The receiver overfills
Suction pressure rises sharply

Correct answer: Head pressure rises because effective condensing surface is lost

Liquid flooding the condenser tubes reduces the surface available for condensing, raising head pressure.

Question 85: What type of heat does refrigerant primarily absorb as it boils in the evaporator?

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

Correct answer: Latent heat of vaporization

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

Question 86: Under ANSI/IIAR guidance, how often should pressure relief valves on ammonia systems typically be replaced?

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

Correct answer: Every 5 years

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

Question 87: After completing maintenance on an ammonia system, how should the technician confirm there are no refrigerant leaks before restarting?

Visual inspection of all fittings is sufficient
Use electronic ammonia leak detector or sulfur stick test, and check all joints at operating pressure (Correct answer)
Smell for ammonia odor only
Pressurize with nitrogen and check pressure drop over 24 hours 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 88: Which EPA regulation requires facilities with more than 10,000 lb of ammonia to prepare a Risk Management Plan?

29 CFR 1910.119
40 CFR Part 68 (Correct answer)
40 CFR Part 82
49 CFR Part 172

Correct answer: 40 CFR Part 68

EPA's Risk Management Program is codified at 40 CFR Part 68.

Question 89: What is the main function of a high-pressure receiver in a refrigeration system?

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

Correct answer: Store liquid refrigerant leaving the condenser

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

Question 90: A compressor is short-cycling (turning on and off rapidly). What is the most common cause?

Excess refrigerant charge
High ambient temperature
Incorrect pressure control setpoint differential or refrigerant undercharge (Correct answer)
Dirty evaporator coil

Correct answer: Incorrect pressure control setpoint differential or refrigerant undercharge

Short-cycling is often caused by a pressure control with too narrow a differential (cut-in too close to cut-out) or low refrigerant charge causing rapid pressure swings.

Question 91: During a routine check, an operator needs to add oil to a screw compressor that is currently in operation. Which of the following describes the safest and most appropriate general procedure?

Use the pressure differential between the oil reservoir and the compressor's low-pressure side to draw oil into the system. (Correct answer)
Slowly pour oil directly into the suction line to be carried into the compressor.
Connect an oil pump to the oil charging valve and pump oil in until the sight glass is full, regardless of system pressure.
Shut down the compressor, vent the crankcase to atmospheric pressure, and pour oil in through the fill port.

Correct answer: Use the pressure differential between the oil reservoir and the compressor's low-pressure side to draw oil into the system.

The standard method for adding oil to an operating compressor is to use the system's own pressure differential. Oil is typically drawn from a container into the low-pressure side of the system (e.g., the crankcase or oil pump suction) by creating a lower pressure in the compressor than in the oil container. This is a controlled method that prevents introducing large amounts of air into the system and avoids the dangers of opening a pressurized system.

Question 92: How does an automatic refrigerated purger separate air from ammonia?

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

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 93: One ton of refrigeration equals how many Btu of heat removal over 24 hours?

144,000 Btu
200,000 Btu
12,000 Btu
288,000 Btu (Correct answer)

Correct answer: 288,000 Btu

A ton is 12,000 Btu/h, which equals 288,000 Btu per 24 hours (the heat to melt one ton of ice).

Question 94: On a pressure-enthalpy (P-h) diagram, the region inside the saturation dome represents what?

Subcooled liquid
Supercritical fluid
Superheated vapor
A liquid-vapor mixture (Correct answer)

Correct answer: A liquid-vapor mixture

Inside the dome refrigerant exists as both liquid and vapor at saturation conditions.

Question 95: What is the main advantage of a computerized maintenance management system (CMMS)?

It schedules work orders and tracks maintenance history in one place (Correct answer)
It automatically recharges refrigerant
It eliminates the need for trained operators
It replaces relief valves

Correct answer: It schedules work orders and tracks maintenance history in one place

A CMMS organizes scheduled tasks, records history, and helps track parts and labor.

Question 96: Raising the evaporator (suction) pressure while keeping condensing pressure constant generally does what?

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

Correct answer: Increases capacity and improves efficiency

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

Question 97: What does a liquid level indicator (sight glass) on an ammonia receiver tell the operator?

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

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 98: An operator in an ammonia refrigeration facility notices that the compressor discharge pressure is consistently higher than normal, even on cool days. The condenser fans are operating correctly and the coils are clean. What is the most likely cause of this issue?

Excessive oil level in the compressor crankcase.
The presence of non-condensable gases in the condenser. (Correct answer)
Overcharge of refrigerant in the system.
A malfunctioning expansion valve.

Correct answer: The presence of non-condensable gases in the condenser.

Non-condensable gases, such as air, nitrogen, or hydrogen, do not condense at the operating temperatures and pressures of the refrigeration system. They accumulate in the condenser, taking up space and increasing the total pressure (Dalton's Law of Partial Pressures). This forces the compressor to work harder, resulting in higher discharge pressures and increased energy consumption.

Question 99: What is the main purpose of a hot gas defrost system on an ammonia evaporator?

Cool the discharge line
Use compressor discharge gas to melt frost from the coil (Correct answer)
Increase refrigeration capacity during peak load
Remove oil from the evaporator

Correct answer: Use compressor discharge gas to melt frost from the coil

Hot gas defrost routes warm discharge vapor through the coil to melt accumulated frost.

Question 100: An ammonia system's suction pressure gauge reads 0 psig. What approximate evaporating temperature does this correspond to for ammonia (R-717)?

0°F
-28°C
+32°F
-28°F (Correct answer)

Correct answer: -28°F

For ammonia (R-717), 0 psig (atmospheric pressure) corresponds to a saturation temperature of approximately -28°F, which is its normal boiling point at atmospheric pressure.

Question 101: Before opening a section of ammonia piping for maintenance, which step is required first?

Increase the system suction pressure
Open the section to atmosphere to check for pressure
Isolate, pump down, and lock out/tag out the section (Correct answer)
Turn off the machine room ventilation

Correct answer: Isolate, pump down, and lock out/tag out the section

Isolating, evacuating, and applying lockout/tagout protects workers from releases of energy and ammonia.

Question 102: Which control device is typically used to maintain a constant evaporating temperature by regulating suction pressure?

Head pressure controller
Evaporator pressure regulator (EPR) (Correct answer)
Discharge check valve
Thermostatic expansion valve

Correct answer: Evaporator pressure regulator (EPR)

An evaporator pressure regulator (EPR) maintains a minimum evaporating pressure, which controls the evaporating temperature in multi-temperature or product-protection applications.

Question 103: An evaporative condenser rejects heat mainly by which process?

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

Correct answer: Evaporation of water sprayed over the coil

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

Question 104: Because ammonia is an EPCRA extremely hazardous substance, what is its Tier II reporting threshold?

1,000 gallons
10,000 pounds
500 pounds or the TPQ, whichever is less (Correct answer)
Any amount present

Correct answer: 500 pounds or the TPQ, whichever is less

For extremely hazardous substances like ammonia, the Tier II threshold is 500 pounds or the threshold planning quantity, whichever is lower.

Question 105: What is the function of a back-pressure regulating valve in a refrigeration system with multiple evaporators at different temperatures?

To maintain a higher evaporating pressure (and temperature) in one evaporator while others run at lower temperatures (Correct answer)
To control refrigerant charge distribution
To equalize pressures across all evaporators
To reduce discharge pressure during peak load

Correct answer: To maintain a higher evaporating pressure (and temperature) in one evaporator while others run at lower temperatures

A back-pressure regulating valve holds a higher suction pressure in a warm-temperature evaporator so it doesn't pull down too cold, while lower-temperature evaporators operate at their own lower pressure.

Question 106: What is the NIOSH recommended exposure limit (REL) for ammonia as a 10-hour TWA?

100 ppm
50 ppm
300 ppm
25 ppm (Correct answer)

Correct answer: 25 ppm

NIOSH recommends 25 ppm TWA with a 35 ppm short-term limit for ammonia.

Question 107: What is the function of the expansion valve?

Measure temperature
Clean the refrigerant
Compress vapor
Regulate refrigerant flow (Correct answer)

Correct answer: Regulate refrigerant flow

The expansion valve, also known as a throttling device, regulates the flow of high-pressure liquid refrigerant entering the evaporator. It reduces the pressure of the liquid refrigerant, causing it to flash into a low-pressure, low-temperature liquid/vapor mixture. This controlled flow ensures efficient heat absorption in the evaporator.

Question 108: Which metal must NOT be used in contact with ammonia in a refrigeration system?

Stainless steel
Cast iron
Copper and brass (Correct answer)
Carbon steel

Correct answer: Copper and brass

Ammonia, especially with any moisture present, attacks copper and copper alloys such as brass.

Question 109: High discharge temperature with normal suction pressure on an ammonia compressor most likely indicates what problem?

Low condenser water temperature
Wet suction (liquid flood-back)
Low refrigerant charge
High suction superheat or discharge valve inefficiency (Correct answer)

Correct answer: High suction superheat or discharge valve inefficiency

High discharge temperature with normal suction pressure often points to excessive suction superheat, leaking discharge valves, or high compression ratio, all of which cause the discharge gas to overheat.

Question 110: A compressor motor is drawing amperage above its full-load rating. Which is the most likely cause?

Low refrigeration load
Compressor running fully unloaded
Low suction pressure
High suction pressure or high discharge pressure overloading the motor (Correct answer)

Correct answer: High suction pressure or high discharge pressure overloading the motor

Higher suction density or higher head pressure increases compressor work, which increases motor current.

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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