HVAC FINAL
The fins on finned tube coils increase heat transfer by:
Increasing the surface area exposed to the air.
The small line on a split system air conditioning unit is the:
Liquid line.
Hydraulic pressures will develop and break compressor parts if:
Liquid refrigerant enters the compressor cylinders.
Broken rods, broken valve plates, broken valves, and broken crankshafts are symptoms of what type of mechanical failure?
Liquid slugging
In a water-cooled condenser, what does an increase in head pressure and increase in temperature difference across the condenser indicate?
Low water flow
Compressor cylinder unloading reduces the capacity of a reciprocating compressor by:
Making the valves in the head inoperative.
Why does oil slugging occur in a compressor?
Oil slugging is caused by a sudden return of large amounts of refrigerant oil.
Where is the liquid receiver located?
On the high side just after the condenser
Refrigeration needs on trucks, tractor-trailers, and shipping containers are equipped with:
Open-drive compressors.
What opens and closes the valves in a reciprocating compressor?
Pressure difference across the valves
The function of the compressor in the refrigeration cycle is:
Raise the pressure and temperature of the refrigerant.
The difference between a liquid receiver and a suction accumulator is that:
Receivers only allow liquid to leave while accumulators only allow vapor to leave.
The purpose of the condenser in a refrigeration system is to:
Reject heat from the refrigerant.
An oil slinger is used with reciprocating compressors that are lubricated by:
Splash lubrication.
A compressor that uses an offset rolling piston, which seals against a blade that remains stationary, and moves in and out of its slot to seal against the rolling piston is:
Stationary blade rotary compressor.
The two refrigerant lines connecting the inside and outside units of a split system air conditioner are:
Suction line and liquid line.
Optional components found on the low side of a refrigeration system include:
Suction line filter, accumulator, and evaporator pressure regulator.
The line that connects the evaporator to the compressor is called the:
Suction line.
Why do water and refrigerant flow in opposite directions in tube-in-tube condensers?
To increase efficiency
What is the purpose of low ambient controls for air cooled condensers?
To maintain a minimum head pressure, even at lower than normal operating conditions
How much would system capacity be increased by subcooling the liquid refrigerant leaving the condenser an extra 12°F?
12°F × 0.5%/°F = 6% increased capacity
Above what temperature do most refrigerant oils begin to break down chemically?
300°F
If the temperature of the refrigerant in a water-cooled system is 95°F, what is the temperature of the leaving water?
85°F
How many BTUs does each pound of water evaporating remove?
970
In which system does less refrigerant enter the cylinder for each compression cycle, requiring more horsepower for each BTU of cooling?
A low-evaporator temperature system
On an R410A air conditioning system, the refrigerant leaving the ________ is 118 psig, 50°F, 100% superheated gas
evaporator
Water conditions which must be monitored to keep a cooling tower system working properly include:
pH, mineral content, and biological growth.
Compared to air conditioning evaporator coils, commercial refrigeration coils have:
Fewer fins per inch.
The two general categories of metering devices are:
Fixed and modulating.
Which of the following is a rarely used metering device that can be used in applications where the load is constant and an operator is present to make manual adjustments?
Fixed valves
An evaporator that covers the coils being cooled with liquid refrigerant is a:
Flooded evaporator.
Chillers can be classified as:
Flooded or direct expansion.
The separation of the refrigerant components in a zeotropic refrigerant when the refrigerant evaporates or condenses is known as:
Fractionation.
What is subcooling?
Lowering liquid refrigerant temperature below its saturation temperature
What types of system access valves do commercial refrigeration systems usually have?
Manual valves on the compressor suction and discharge and on the liquid receiver
Internally equalized thermostatic expansion valves:
Measure the evaporator pressure through a passageway inside the valve.
A compressor that compresses gas between a fixed spiral and an orbiting spiral is a:
Scroll compressor.
An R22 refrigeration system requires a superheat of 8°F. If the evaporator saturation pressure is 43 psig, what should the bulb temperature be?
28°F
Which of the following is the standard saturated temperature drop in the suction line?
2°F
What is the maximum reading on a typical R410a compound gauge?
300 psig
Leaks in commercial refrigeration systems must be repaired if they have an annual leak rate of:
35% of the charge per year.
Leaks in industrial process cooling systems must be repaired if they have an annual leak rate of:
35% of the charge per year.
What is the maximum safe fill weight of a recovery cylinder with a tare weight of 30 pounds, a water capacity of 40 pounds, holding a refrigerant with a specific gravity of 1.2?
40 lbs × 0. 8 × 1.2) + 30 lbs = 68 lbs (rounded)
What is the maximum safe amount of refrigerant for a recovery cylinder with a water capacity of 50 pounds, holding a refrigerant with a specific gravity of 0. 9?
50 lbs × 0. 8 × 0. 9 = 36 pounds
What is the maximum reading on a typical R22 high pressure gauge?
500 psig
A system using R-404a has an evaporation temperature of 0°F. If the line length is 100 ft. and the system needs a capacity of 2 tons, what size line should be used?
7/8 in
What types of system access valves do household refrigerators usually have?
A process stub on the compressor
Most type I systems evacuated and charged at the factory through:
A process tube or process stub.
Which is the primary purpose of a split-system installation valve's service port? A) System evacuation B) Valve maintenance C) Controlling leaks D) Trapping refrigerant
A) System evacuation
Oil accumulation in the evaporator:
Acts as an insulator reducing the heat transfer of the coil.
Which of the following modifications would alleviate refrigerant migration in a long-line system?
Adding a liquid line solenoid
The three basic types of condensers used with HVACR systems are:
Air cooled, water cooled, and evaporative.
When calculating the effect of temperature change on a standing charge:
Always use absolute pressure and temperature.
Ball valves on the end of refrigeration hoses:
Are controlled manually by the technician.
To prevent liquid slugs from leaving the evaporator and entering the compressor, direct expansion evaporators:
Are typically fed at the bottom with suction gas leaving at the top.
Refrigerant leaves the metering device:
As a saturated mixture of liquid and vapor.
Where is the suction line temperature read when adjusting a TEV?
As close as possible to the TEV bulb
What is the advantage of balanced port TEVs?
Balanced port valves can retain good control over a wider range of operating conditions.
What type of water cooled condenser is easiest to clean?
Shell and tube
Why are liquid line filter-driers required for all systems using HFC refrigerant?
Because the POE oil used with HFC refrigerant is very hygroscopic
To prevent the system refrigerant from quickly dropping in temperature and pressure, refrigerant recovery should:
Begin with liquid
Water that condenses on an evaporator coil and is blown off by the velocity of the air through the coil is called condensate:
Blowoff.
Refrigerants release heat:
By condensing from a vapor to a liquid.
Refrigerants absorb heat:
By evaporating from a liquid to a vapor.
How is the type of service pressure of a recovery tube identified?
By the last group of numbers on the tube
The percentage of air that travels through a tube and fin coil without touching any coil surface is called the:
Bypass factor.
The refrigerant in a mechanical compression refrigeration system absorbs and releases heat by:
Changing its physical state.
The preferred method for raising the pressure of a low pressure chiller in order to test for leaks is:
Circulating warm water through the chiller.
The first check to make whenever working on a water-cooled system is:
Condenser water flow.
Why is it important to measure the vacuum level on the system?
To determine when evacuation is complete
Liquid refrigerant should always be recovered first from chillers:
To keep from freezing the water in the chiller tubes.
Why do some technicians recommend using a separate refrigerant tank when purging hoses?
To preserve the system charge.
Water cooling evaporator constructions include:
Tube in tube, Shell and coil, and Shell and tube.
To increase superheat on a thermostatic expansion valve, the adjusting stem should be:
Turned clockwise.
To increase the evaporator pressure, the adjustment on top of an automatic expansion valve should be:
Turned clockwise.
What type of units are only required to have process stubs?
Type 1 only.
What type of units are required by the EPA to have service valves?
Type II and Type III
All refrigerants with a three-digit number starting with the number 4 are:
zeotropic blends.
The possible fine for violating the clean air act is:
$37,500 per incident.
In a parallel compressor system, oil often does not return at the same rate to all of the compressors because:
All the compressors do not operate for the same length of time.
What is an oil lift?
An oil lift is a trap at the bottom of a vertical suction riser.
A fluorinated refrigerant whose number starts with a 1 is:
Compound.
Fan cycling, fan speed control, damper control, and condenser flooding are different types of:
Condenser Low ambient controls.
The lines inside the saturation curve that start at the bottom and extend upward toward the critical point are called:
Constant Quality lines.
Which pressure relief device works primarily by temperature?
Fusible plug
How are trigger rates established?
by the speed of loss
How does a reciprocating compressor operate?
In a reciprocating compressor, the piston is driven up and down in the cylinder by the connecting rod and crankshaft.
The most common hazard encountered when installing and removing refrigeration gauges is:
frostbite
What pressure units are used on the enthalpy diagram?
psia
One difference between refrigerant piping practices for air conditioning systems and refrigerant piping practices for commercial refrigeration systems is that:
Most air conditioning manufacturers do not recommend oil traps
Technicians have been required to pass an EPA certification exam to handle refrigerant since:
November 14, 1994.
The purpose of the trap in a condensate drain is to:
Offset the negative pressure on the drain that can prevent the water from draining.
The small gaps between the screws on the screw compressor are sealed by:
Oil flooding.
The saturation temperature of the refrigerant in the system can be read on the refrigeration gauges:
On the inside colored scales of the gauge.
The EPA requires the repair of refrigerant leaks:
Only in systems with a refrigerant charge greater than 50 pounds.
All refrigeration compressors are designed to pump:
Only vapor.
Automatic expansion valves are good at maintaining a constant:
Temperature.
Azeotropes are mixtures of two refrigerants:
That do not separate when changing state.
Zeotropes are mixtures of two or more refrigerants:
That separate when changing state.
Which of the following is a type of sports arena that uses flooded evaporators?
Ice rinks
The hot gas lines need to be insulated:
If they are exposed to cold temperatures that could cause the refrigerant to condense in the line.
Liquid lines need to be insulated:
If they travel through an unusually hot space.
When connecting a recovery system for push-pull liquid recovery, the outlet of the recovery unit is connected to:
The discharge service valve on the system.
Why are split-system installation valves typically not used following installation?
They do not control flow to service ports.
How do the three position service valves differ from other valves?
They have no closed position.
In leak detection, R-22 is used in conjunction with which of the following?
With electronic detection
On a typical plot of the refrigeration cycle, where does liquid refrigerant first begin forming in the condenser?
Where the condenser line (the top line) crosses the saturation curve from the superheated region
A TEV with a dead power element will operate:
With a high superheat.
Using a coil cleaning chemical incorrectly can result in:
Creating leaks in the condenser.
What type of compressors contain the compressor and motor together inside a welded steel housing?
Hermetic compressors
Why is it necessary to purge gauge manifold valves while they are connected?
To prevent contamination of the system
Check valves on the end of refrigeration hoses:
Automatically open and close when the hoses are connected and disconnected.
A refrigerant sensor that changes conductivity when exposed to refrigerant is:
Ceramic metal oxide semi-conductor (CMOS).
How does a hot gas defrost system work?
Hot compressor discharge gas is routed to the evaporator.
Why is back-seating a manual service valve when installing a gauge manifold necessary?
So that there is no pressure on the gauge port
Subcooling the liquid refrigerant increases system efficiency by:
Insuring a solid stream of liquid to the metering device.
The discharge, liquid, and suction lines of a packaged unit are:
Located inside the unit.
The pressure drop due to vertical lift in a liquid line is approximately:
0. 5 psi per foot of lift
What is the maximum reading on a typical R22 compound gauge?
120 psig
How many microns are there in an inch?
25,400
Medium-temperature applications are usually between:
28°F to 40°F.
For most systems, the minimum velocity in a horizontal suction line is:
750 - 1000 feet per minute.
What is the maximum safe fill level for a refillable refrigerant cylinder?
80%
The operating mechanism inside most refrigeration gauges is:
A bourdon tube.
Which refrigeration device would most likely be installed in the discharge line leaving the compressor to prevent liquid refrigerant from draining from a raised condenser into the compressor head?
A check valve
The low side gauge is called:
A compound gauge.
A compound is a combination of two or more chemicals:
A compound is a combination of two or more chemicals:
A bourdon tube is:
A flattened tube in the shape of a question mark that straightens under pressure.
A tool used for checking system pressures, evacuating systems, recovering systems, and charging systems is:
A gauge manifold.
Flash gas in the liquid line can be identified by:
A significant temperature drop in the liquid line temperature.
A product that is fully manufactured, charged, and hermetically sealed in a factory with five pounds or less of refrigerant is defined as:
A small appliance.
Commercial refrigeration systems normally have:
A suction service valve, discharge service valve, and a king valve.
A fluorinated refrigerant whose number starts with a 5 is:
Azeotropic
The operation of a thermostatic expansion valve can best be described as:
Bulb pressure = evaporator pressure + spring pressure.
The four parts of the EPA Certification exam include:
Core, Type I - small appliances, Type II - high pressure and very high pressure appliances, and Type III - low pressure appliances.
Which of the following is an indicator of a leaking refrigerant system? A)Higher than normal temperature readings B)Metal-to-metal contact points C) Visible line bracing D) Front-seated system valves
Correct Answer B)Metal-to-metal contact points
Which of the following statements is true? A)During part load operation, refrigerant is forced through the smaller riser. B)During part load operation, refrigerant is forced through the larger riser. C)During full load operation, refrigerant is forced through the larger riser. D) During full load operation, refrigerant is forced through the smaller riser.
Correct Response A) During part load operation, refrigerant is forced through the smaller riser.
For which of the following is the last part of the evaporator used? A)Increase the vapor percentage B)Superheat the refrigerant C)Lower the liquid percentage D) Raise the liquid percentage
Correct Response B) Superheat the refrigerant
It is possible for the same air conditioner to have a different capacity and efficiency with each coil it is matched to, A) True B) False
Correct Response A) True
Besides distributing the refrigerant evenly, a refrigerant distributor also:
Creates a pressure drop across the distributor.
The system capacity of an air conditioner with a fixed metering device:
Decreases when the indoor wet bulb temperature rises.
What is the material inside the filter-drier called?
Desiccant
An evaporator in which refrigerant enters as a saturated liquid vapor mix and leaves as a superheated vapor is a:
Direct expansion evaporator.
A self contained recovery device:
Does not rely on the system the refrigerant is being recovered from for its operation.
How is entropy defined in refrigeration?
Entropy is the ratio of heat content to absolute temperature.
Why might leak testing with nitrogen be preferable to using R-22?
Environmental concerns.
Refrigeration system component that absorbs heat out of the product is the:
Evaporator.
Adiabatic expansion means:
Expanding without adding heat.
The temperature difference between the bubble point and the dew point of a zeotropic refrigerant is called:
Glide.
Where in the system is an oil separator installed?
In the discharge line leaving the compressor
Where in the cycle does heat enter the refrigerant?
In the evaporator and compressor
When connecting a gauge manifold set, the air inside the hoses and gauge manifold:
Is removed by purging.
Why can a compound gauge not indicate when a system is properly evacuated?
It can only show inches and there are 25,400 microns in one inch.
Why has the use of halide torches in leak detection decreased in popularity?
It does not work with most modern refrigerants.
On a commercial refrigeration system with electric defrost, what does the compressor do during the defrost cycle?
It shuts off.
Which of the following is considered an advantage of a flooded evaporator?
Its ability to maintain a very accurate temperature across the entire evaporator surface
It has been illegal to vent ozone depleting refrigerants from stationary equipment since:
July 1, 1992.
Which metering device used on flooded evaporators opens when more refrigerant evaporates, enabling the refrigerant to flow into the evaporator?
Low side float
Which type of metering device used on flooded evaporators opens to admit more liquid refrigerant into the evaporator when the liquid level in the evaporator drops?
Low side float
Small Domestic refrigerators and freezers use:
Plate evaporators.
What is the possible error for a gauge that has a 1% of full scale accuracy if the gauge reads up to 300 psig?
Plus or minus 3 psi
The outer scale on most gauges reads:
Pressure.
Valves that open and close rapidly under the control of electronic circuits are:
Pulse modulated valves
The blue gauge and hose on a gauge manifold set are used for:
Reading pressures on the low side of the system.
Refrigerant that has been reprocessed to at least the purity specified in the ARI Standard 700 is considered:
Reclaimed refrigerant
After servicing a system using bolt-on piercing valves, the technician should:
Recover the refrigerant, remove the bolt-on valve and replace it with a permanent valve.
A mechanical refrigeration system cools a room by:
Removing heat from the room.
The pressure lines on the P-H diagram:
Run horizontally from the left to right.
Which pressure relief device is essentially an engineered weak point?
Rupture disk
How is a brine solution created?
Salt and water.
What types of system access valves do residential air conditioning systems usually have?
Shrader valves on the suction line and liquid line
Air conditioning tube and fin coils are commonly available as:
Slant coils, "A" coils, and "N" coils.
Bourdon tubes work by:
Straightening on a rise in pressure and curling on a fall in pressure.
The refrigerant line whose sizing has the most effect on the compressor's compression ratio is the:
Suction line
Thermostatic expansion valves respond to changes in:
Superheat.
Refrigerant enters as a saturated mixture and leaves as a:
Superheated vapor.
Why might there be a negative pressure on the condensate outlet in a coil operating at a positive static pressure?
The air pressure can create negative static pressure.
A micron vacuum gauge indicates:
The amount of absolute pressure remaining in the system.
All of the liquid refrigerant has vaporized by:
The end of the evaporator.
Refrigerant oil flow through the liquid line is not a problem because:
The oil mixes with the liquid refrigerant.
In a direct expansion chiller:
The water is in the shell and the refrigerant is in the tubes.
In a flooded chiller:
The water is in the tubes and the refrigerant is in the shell.
How is MVAC certification established?
Through separate certification
Which legal framework calls for a prohibition on venting ozone depleting refrigerants, restrictions on the sale of ozone depleting refrigerants, and certification of recycling and recovery equipment and technicians?
Title VI of the Clean Air Act
Why is a pressure regulator necessary when using nitrogen cylinders?
To reduce the pressure in the nitrogen cylinder to a safe level
Why are positive shutoff devices used when removing gauge manifold sets from Schrader valves?
To reduce the release of refrigerants
If a technician needs to read the refrigerant pressure of a window unit, they must:
Use a piercing valve.
One way to reduce the amount of refrigerant spray when connecting and disconnecting refrigeration hoses from Schrader valves is to:
Use positive shut off hoses.
What is the best pH level to maintain in a water tower?
Between 6.5 and 9
Operating a hermetic compressor in a vacuum:
Can cause the motor to arc out because of the change in electrical resistance.
A compressor that uses an impeller to throw refrigerant from the center outward is a:
Centrifugal compressor.
Cooling towers in which the water circulating in the tower is separate from the water circulating through the condenser are called:
Closed loop cooling towers.
What units are used to indicate specific enthalpy?
BTUs / lb / ⁰R
The required system capacity in tons can be determined by dividing:
200 BTUs/min by the system's refrigeration effect.
An R-22 system has a 28-ft lift and a 7 psi pressure drop in the liquid line due to vertical lift. If the liquid leaves the condenser at 244 psi, what is the pressure at the top of the vertical lift?
223 psi 244-28+7=223
The smallest increments displayed on most digital gauges are:
0.1 psi.
The most accurate analog gauges available on gauge manifolds in the HVACR industry are:
1% of full scale.
Which of the following is the range of fin spacing on low-temperature coils?
1-4 fins per inch
For most systems, the minimum velocity in a vertical suction line is:
1000 - 1500 feet per minute.
What is the refrigeration effect of a system if the liquid entering the evaporator has an enthalpy of 60 BTU/lb and the vapor leaving the evaporator has an enthalpy of 110 BTU/lb?
110 Btu/lb - 60 Btu/lb = 50 Btu/lb
What is the maximum safe storage temperature for refrigerant cylinders?
125°F
Leaks in air conditioning systems must be repaired if they have an annual leak rate of:
15% of the charge per year.
Leaks in refrigeration systems other than air conditioning systems, commercial refrigeration systems, or industrial process cooling systems must be repaired if they have an annual leak rate of:`
15% of the charge per year.
If the low side test pressure is not know, the maximum pressure that should be used for leak testing an R-22 refrigeration system with hermetic compressor is:
150 psig.
A refrigerant blend with a glide of 10°F or more would be considered:
A high glide blend.
A refrigerant blend with a glide of 2°F or less would be considered:
A low glide blend.
What are the parts of a distributor?
A nozzle, conical divider, and multiple holes around the divider cone
The maximum pressure drop for a suction line should not exceed:
A corresponding saturation temperature drop of 2°F.
Which of the refrigerant ratings indicates that a refrigerant is considered a higher toxicity refrigerant?
B1
What refrigerants can be detected with a halide torch?
CFCs and HCFCs
One operating advantage of fixed restriction metering devices over expansion valves is:
Can be used with low starting torque compressor motors.
Oversized suction lines:
Can cause poor oil return because of low refrigerant velocity.
Undersized suction lines:
Can reduce system efficiency because of a high pressure drop.
Two types of fixed metering devices are:
Capillary tubes and orifices.
As refrigerant passes through the metering device, it:
Drops in pressure and temperature.
Commercial refrigeration equipment for ice cream storage typically uses:
Low temperature evaporators.
The most common types of defrost for commercial refrigeration evaporators are:
Electric and hot gas defrost.
What type of sensor is most often used to detect very low parts per million for toxic refrigerants?
Electrochemical sensors (EC)
Ground up aluminum can react violently with which of the following?
HFC
Small appliances such as household refrigerators and freezers now primarily use:
HFC-134a.
New residential air conditioning systems now primarily use:
HFC-410A.
A system with a loose TEV sensing bulb would most likely:
Have a low superheat.
Key safety information include:
Hazard identification Exposure control Emergency call number First aid Chemical placement on the periodic table
Why are heated diode leak detectors better than corona discharge leak detectors?
Heated diode leak detectors are not as prone to false alarms.
An overfeeding metering device can cause?
High suction pressure, low superheat, and low subcooling
Commercial refrigeration equipment for dry storage typically uses:
High temperature evaporators.
The wet coil static pressure drop is:
Higher than the dry coil static pressure drop.
Leaks on the low side of a Type III system are indicated by:
Increased purge operation.
n an air conditioner with a fixed metering device, a decrease in the outdoor ambient causes:
Increased system superheat.
Increasing the airflow across a coil:
Increases the bypass factor.
Increasing the airflow across a coil:
Increases the sensible capacity.
Increasing the airflow across a coil:
Increases the static pressure drop across the coil.
Why is the push-pull method of recovery preferable for some systems with large quantities of refrigerant?
It is the quickest method
Why does a pressure drop not necessarily indicate a refrigerant leak?
It may be indicating temperature change.
In which way did Title VI, Section 608 of the Clean Air Act additionally regulate refrigerant technicians?
It required that they hold a certification.
What units are used to measure pressure in the SI system?
Kilopascals (kPa)
Creates a pressure drop across the distributor.
Large Chillers.
Flooded evaporators are used in:
Large chillers.
When connecting gauges to an already installed and operating unit with split system installation valves, the installation valves should be
Left alone.
What is considered a long line application for residential air conditioning?
Lines exceeding 80 feet in length or with a vertical rise of more than 20 feet
A restricted inlet screen on a TEV can cause:
Low suction pressure, high superheat, and high subcooling.
Commercial refrigeration equipment for eggs, produce, and dairy uses:
Medium-temperature applications.
Refrigerant increases in volume as it travels through the:
Metering device
Which of the following is the line that drops straight down because no heat is gained or lost?
Metering device
Which type of metering device is able to respond to changes in system operations?
Modulating metering devices
What are the most common desiccant materials used in driers?
Molecular sieve and activated alumina
What is the general formula for calculating the effect of temperature on a holding charge?
New temperature/starting temperature × starting pressure
Third party testing for recovery units has been required since:
November 15, 1993.
It become illegal to vent replacement refrigerants in:
November 15, 1995
The high pressure gauge reads:
Only pressures above atmospheric pressure.
When should gauges be installed on small critically charged systems?
Only when other diagnostic means have been exhausted
Besides improving efficiency, insulating the suction line:
Prevents moisture from condensing on the line.
Which type of glove should be used if prolonged contact with liquid or gas is expected?
PVA
What units are used to measure pressure in HVACR systems in the United States?
Pounds per square inch gauge (psig)
The factors that must be considered when sizing the discharge line are:
Pressure drop and velocity.
Automatic expansion valves are similar in operating concept to:
Pressure regulators.
.Refrigerant characteristics shown on a pressure-enthalpy diagram include:
Pressure, heat, and temperature.
Thermostatic expansion valves are designed to maintain a constant:
Pressure.
The compound gauge reads:
Pressures above and below atmospheric pressure.
Refrigerant that has been removed in any condition from an appliance and stored in an external container without necessarily testing or processing it in any way is considered:
Recovered refrigerant.
Refrigerant that has been removed from an appliance and cleaned for reuse without meeting all of the requirements of ARI-700 is considered:
Recycled refrigerant
To increase latent cooling capacity:
Reduce the airflow over the evaporator.
Sensible cooling:
Reduces the air temperature.
When the hand wheels on the gauge manifold are turned counter clockwise:
Refrigerant can flow between the outer hoses and the center hose.
A device used to evenly distribute mixtures of liquid and vapor refrigerant leaving the TEV to multiple evaporator circuits is called a:
Refrigerant distributor.
Positive shutoff fittings allow technicians to reduce the amount of which of the following?
Refrigerant spray when disconnecting from a refrigeration system
As the refrigerant temperature drops during the desuperheating phase of the refrigeration cycle, the refrigerant pressure:
Remains the same.
Latent cooling:
Removes water from the air.
Which pair of factors most directly affects the maximum allowable pressure drop within a system?
Temperature of refrigerant and type of refrigerant
When installing a double riser in a commercial refrigeration system, which of the following statements is true?
The combined areas of the risers should be equal to the area of the suction line.
Which refrigeration hose end has a Schrader valve core depressor?
The crooked end
What controls the length of the defrost cycle on most commercial refrigeration systems?
The defrost termination thermostat
What happens to the evaporator fan motor when the defrost cycle is terminated?
The fan shuts off until the defrost termination thermostat senses that the evaporator is cold again.
A refrigeration system dataplate states that the low side test pressure is 150 psig. This means that:
The low side should not be pressurized above 150 psig.
Why is it dangerous to drill out orifices in metering devices?
The orifices are conical in shape.
Why do standard design thermostatic expansion valves need a minimum pressure drop to operate correctly?
The pressure difference across the pin acts as an opening force.
How can a technician determine when a filter-drier is stopped up and needs changing?
The pressure drop will exceed 2 psig
How is recovering into a receiver accomplished?
The refrigerant is pumped into the receiver with the king valve closed
Modifications such as adding a liquid line solenoid at the outdoor unit, using a hard shutoff thermal expansion valve at the evaporator, and adding a compressor hard start kit are recommended when:
The refrigerant line length is over 80 feet.
Why are vertical suction risers often smaller than the horizontal runs on the same suction line?`
The risers are sized smaller to maintain a minimum velocity to lift the oil.
When a manual service valve is back seated
The service port is closed and the system is open to the line.
When a manual service valve is front seated:
The service port is open and the system is closed to the line.
What two pieces of information are necessary to measure the TEV superheat?
The suction line temperature and pressure
An isothermal process is a process which does not change:
The temperature of the refrigerant
A refrigerant's enthalpy is:
The total amount of heat in the refrigerant.
When connecting a recovery system for push-pull liquid recovery, the inlet of the recovery unit is connected to:
The vapor valve on the refrigerant recovery cylinder.
What is the problem associated with disconnecting a gauge manifold through its middle leg?
There is a loss of refrigerant.
Why will the compressor on a leaking system become overheated?
There is a reduced amount of coolant.
What senses the line temperature in electronic expansion valves?
Thermistors
Which of the following metering devices can respond to changes in system conditions?
Thermostatic expansion valve
What advantages do orifice type metering devices have over capillary tubes?
They are easy to change.
Why are some reclaimed refrigerants classified as hazardous materials?
They are mixed with other oils.
What controls when Shrader valves open and close?
They open and close when hoses with depressors are connected and disconnected to them.`
What controls when manual backseating valves open and close?
They open when they are backseat cracked and close when they are backseated.
What is the purpose of TEV sensing bulbs with a limited, or gas charge?
They produce a maximum operating pressure at high operating superheat.
How do the recovery levels for Type III equipment differ from recovery levels for other types of equipment?
They require lower vacuums than for other types.
Commercial refrigeration equipment for storing viral cultures typically uses:
Ultra low temperature evaporators.
Which leak detectors can be used with systems that are only charged with nitrogen?
Ultrasonic leak detectors
When do positive shut-off fittings reduce refrigerant loss?
When connecting and disconnecting hoses
Capillary tube metering devices are commonly used today in:
Window units.
What difference is there between handling zeotropes and azeotropes?
Zeotropes must leave the cylinder as a liquid but azeotropes may leave the cylinder as either a liquid or a vapor.
A fluorinated refrigerant whose number starts with a 4 is:
Zeotropic.
backseated and frontseated?
back; counterclockwise, service port is closed but middle port is open. Front: clockwise, line port is closed but the middle port is open to the service port.
The refrigerant is a high-pressure, warm, subcooled liquid at the inlet of the metering device. The state of the refrigerant is:
100% liquid.
How much heat is rejected through condensation?
80%
If the refrigerant condensing saturation temperature is 100°F at the start of the process, what would the entering water temperature be?
80°F
If the water entering a water cooled condenser is 80°F, what would the leaving water temperature be?
90°F
One technique for improving efficiency and comfort through compressor selection is to select:
A compressor with capacity control to match the compressor capacity with the refrigeration load.
Which type of condenser uses a fan to push air across the condenser?
A forced-draft air-cooled condenser
Which compressor has a piston that is driven up and down in the cylinder by a connecting rod and crankshaft?
A reciprocating compressor
Which compressor type draws refrigerant gas in through the inlet port into voids created by turning rotors?
A screw compressor
What is the difference between the compressor operating temperatures in an air-cooled condenser and a water-cooled condenser?
A water-cooled condenser operates 15°F below an air-cooled condenser.
How does a two-step scroll compressor achieve capacity reduction?
An internal rotating plate opens and closes two drilled ports in the scroll.
Why do some commercial buildings need air conditioning in the winter?
Commercial buildings often have large internal heat loads from people, lights, and machines.
The order of the four main components of the refrigeration cycle is:
Compressor - condenser - metering device - evaporator.
Which of the following would have the greatest effect on the heat content of the refrigerant? A) The refrigerant's humidity B) The refrigerant's state C) The refrigerant's temperature D) The refrigerant's pressure
Correct Answer B) The refrigerant's state
Which of the following is true of a medium-temperature refrigeration unit? A) It requires 1 hp to produce 1-1/3 tons of cooling. B) It requires 1 hp to produce 1 ton of cooling. C) It requires 1 hp to produce 1/3 ton of cooling. D) It requires 1 hp to produce 2/3 ton of cooling.
Correct Answer D) It requires 1 hp to produce 2/3 ton of cooling.
Which of the following has the capacity range for a centrifugal compressor? A) Residential AC B) Commercial AC C) Appliance D) Refrigeration
Correct Response B) Commercial AC
An evaporative condenser: A) Is really just another name for evaporator. B) Works by evaporating refrigerant to cool the condenser coil. C)Works by evaporating water to cool the condenser coil. D) Cools air through the evaporation of refrigerant inside the condenser.
Correct Response C) Works by evaporating water to cool the condenser coil.
Which of the following compressors is not considered a positive displacement compressor? A) Reciprocating B) Screw C) Rotary D) Centrifugal
Correct Response D) Centrifugal
Which of the following systems uses compression pumps and condensers to cool the air? A) Evaporative system B) Thermoelectric system C) Absorption system D) Mechanical compression system
Correct Response D) Mechanical compression system
As the refrigerant passes through the condenser, the refrigerant is:
De-superheated, condensed from a gas to a liquid, and subcooled.
The main cause of high condensing temperature and pressure in air cooled condensers is:
Dirty condensers.
Optional components on the high side of a refrigeration system include:
Discharge line muffler, oil separator, liquid receiver, and liquid line filter-drier.
The line that connects the compressor to the condenser is called the:
Discharge line.
The heat rejected by the condenser:
Equals the heat absorbed by the evaporator plus the heat added by the compressor.
Which of the four types of refrigeration systems cools the air without removing any heat from the air?
Evaporative systems
The four types of cooling mechanisms are:
Evaporative, Thermoelectric, Absorption, Mechanical Compression.
A system operating with a suction line superheat of 5° or less is probably:
Experiencing flooding.
A common application for centrifugal compressors is:
Industrial process chilling.
What is the purpose of a cooling tower?
It cools the water flowing through it by evaporating a small portion of the water.
Refrigeration can be defined as:
It moves the heat from the refrigerated area to another area.
Gas trapped in the compressor clearance space is expanded at the beginning of the suction stroke. What effect does this have on the system?
It reduces compressor capacity
The line that connects the condenser to the metering device is called the:
Liquid line.
Where is the suction accumulator located?
On the low side just before the compressor
A compressor crankcase heater is used to:
Prevent off cycle refrigerant migration to the compressor crankcase.
The major types of compressors listed by mechanical design are:
Reciprocating, rotary, scroll, screw, and centrifugal.
A compressor that uses a large off-center rotating shaft and multiple blades that follow the cylinder walls as the shaft rotates is a:
Rotating blade rotary compressor.
The primary cause of high condensing temperatures in water cooled condensers is:
Scaled and fouled condenser surfaces.
In a water-cooled condenser, what does an increase in head pressure and a decrease in temperature difference across the condenser indicate?
Scaling on tubing
Three different design screw compressors are:
Single screw with gate rotors, dual screw, and triple screw.
Assuming they both have the same condenser temperature, which application requires more horsepower to produce a ton of cooling: a 0°F evaporator or a 40°F evaporator?
The 0°F evaporator because of the higher pressure difference
The space left between the piston and the valve plate of a reciprocating compressor when the piston is at the top of the cylinder is called:
The clearance volume.
What is the primary difference between air cooled condensers on standard efficiency systems and air cooled condensers on high efficiency systems?
The coil size is increased to increase the heat transfer area.
What is the primary advantage of a remote air cooled condenser on an ice machine?
The heat generated by the ice machine is expelled outside instead of in the kitchen.
Which of the two refrigerant lines going to the compressor is larger?
The low pressure suction line
What is the lowest percentage of full capacity that a digital scroll can be safely operated for extended periods?
The minimum capacity is 10% to insure that the compressor gets proper lubrication.
An advantage of open drive compressors is that:
The motor and compressor can be replaced separately.
The advantage of compliance in a scroll compressor is that:
The orbiting scroll can separate and unload to pass a small liquid slug.
If the refrigerant is recovered improperly from a water-cooled condenser:
The water may freeze.
How can scaling be reduced in water towers?
There is a small amount of water drained off the cooling tower sump.
How can semihermetic compressors be characterized?
They have a bolted housing that encloses both the compressor and motor.
How can hermetic compressors be characterized?
They have a welded shell which holds both the compressor and motor.
Why are biocides added to cooling-tower water?
To reduce biofilm
The three types of air cooled condenser coil construction found on residential air conditioning units today include:
Tube and fin, spiney fin, and microchannel.
Which type of condenser generally operates with a lower discharge pressure?
Water cooled condensers
Tube in tube, shell and coil, and shell and tube are all different types of:
Water cooled condensers.
Which type of condenser requires the most maintenance?
Water-cooled condensers
Rotary compressors are commonly used in:
Window units.
When cleaning an air cooled condenser:
You should wash opposite the direction of airflow.
