Study Flashcards
I you increase the pressure of a liquid, its____ temperature will _____ meaning that it will boil at a higher temperature.
saturation; increase
At a temperature of -30°F, the enthalpy of the saturated liquid refrigerant (hr ) is 3.5 Btu/b. The
enthlapy of evaporation (hip ) is 87 4 Btu/b What is the enthalpy of the saturated vapor (hg )?
90.9 Btu,lb
In the following diagram of a refrigeration cycle, the line between points_____ represents the amount of subcooling.
2&3
Choose values from the list below when making your calculations:
Condensing pressure = 232 psia
Evaporating pressure = 61 psia
Refrigerating effect = 62 Btu/lb
Enthalpy of condenser pressure = 115 Btu/lb
Enthalpy at evaporator pressure = 98 Btu/lb
One ton of refrigeration - 200 Btu/min
One horsepower = 33 000 ft 1b/min -
- 42 4 Blu/min
10.3Hp
Liqund tefugerant can be subcooled by transferring hot euther to the atmosphere in the condenser or to the____
It tho suction line heat exchanger
Refrigerant vapor
In the ASHRAE standard designations of refrigerant, the
Letter R is being replaced by letters identifying the chemical structure
Temperature glide occurs only in____
refrigerants
Blended
ASHRAE classifies refrigerants according to how hazardous they are. The most hazardous refrigerants are rated____
B3
When handling out and storing refrigerants , you must protect yourself by
avoiding any open flame
The ozone layer in the earths atmosphere is important, because it
Absorbs ultraviolet radiation from the sun
CFCs contribule to the greenhouse effect by
absorbing infrared radiation
In order to minimize the release of CFCs into the atmosphere, refrigeration service technicians must
recyele refrigerants on-site, if possible
A recycled refrigerant may be placed in
The system from which it was removed
During The installation of a new system lhe chance of future refrigerant leaks can be reduced by
installing a muffler in the compressor discharge line
 To reduce the depletion of the ozone layer, the U.S. government has implemented laws requiring the
testing and certification of all technicians whose work can cause the
release of harmful refrigerants.
The EPA’s final rule concerning the handling of refrigerants and refrigeration equipment requires
certifying the equipment used in recycling and reclaiming refrigerants
The compressor for an active recovery system is part of the_____ The compressor for a passive recovery systern is part of the____
recovery equipment; systern being serviced
Technicians who work on residential air conditioning systems must have at least_____certification
Type ll
Which of the following documents is required by the FPA?
Certification activity report
Which of the following is a conlaminant that can be removed by a filter-drier?
Acid
An absorption type desiccant holds water by means ol a(n)_____ action, but an adsorption-type desiocant holds water by means of a(n)____action.
Chemical; mechanical
If you mount a filter-drier in a vertical suction line the mlet should be located at the top so that____cannot become lapped inside.
Oil
When selecting a filter-drier, you need lo base your selection in part on the
minimum particle size it can trap
When installing a filter-drier in a refrigeration system, you should
wear safety goggles
You can pinpoint leaks in a new refrigeration system by charging the system with_____ and using a _____
Nitrogen, soap solution
When preparing to us a gauge manifold in servicing a pressurized refrigeration system, you connect its high side charging hose to the
Compressor discharge service valve
To check the charge in a refrigeration system vou can look al the______ in the liquid lines. If the change is low you will probebly see
sight glass; bubbles
In using the deep-vacuum method of dehydrating a refrigeration system, you lower the pressure to about _____ microns or less. With the vacuum pump turned off a gradual rise in to about pressure lells you the system is
1,000; not dry
You can tell whether you have charged a refrigeration systern with the correct amount of refrigerant by checking the
weight of the refrigerant used
The miscibility of a refrigerant oil is its abilty to
mix with the refrigerant
Oil that becomes mixed will the refrigerant in a system can cause which of the following problems?
Clogged desiccant
 An oil separator is located between the_____the______ in order to keep oil out of the condenser and evaporalor
compressor: condenser
Moisture in a refrigeration systom causes a variety of problems, including
blockage in cold parts of the system
Belore you check the oil level in the sight- glass on a relrigeration comprossor, you should stop the compressor for at least____ The compressor should be____
while you check the oil level
ten minutes: stopped
Which of the following is a kind of kinetic-displacement compressor?
Centrifugal
Which of the following is part of a scroll compressor?
Swing link
A multiple stage refrigeration system has more than one
Compressor
When selecting a replacement compressor you need to make sure the replacement will operate
(with/at) the proper
Discharge pressure
Among reciprocating compressors, the crankshaft is usually vertical in a(n)_____
compressor, but horzontal in a(n)_____
compressor
full-hermetic, open
On the pistons of reciprocating compressors, the______ ring(s) prevent oil from reaching the compression chamber. The_____ ring(s) prevent refrigerant from escaping around the piston during compression.
Bottom; top
Which of the following is a method of distributing lubricating oil in a reciprocating compressor?
Crankshaft splash
A cylinder unloader reduces the capacity of a reciprocating compressor by allowing refrigerant to Now through the_____
port during the____stroke.
suction; compression
One way of reducing vibration problems in reciprocating compressors involves the use of
spring mounts
One advantage of rotary compressors over reciprocating compressors is that the
Vibration is less
Slugging is the entry of______
collapse of______refrigerant into a compressor Cavitation is the formation and in a liquid flowing under pressure.
liquid; vapor pockets
One purpose of the accumulator on a rotary compressor is to
keep dirt and debris out of the compressor
Helical compressors differ from rotary compressors in that they have
No vanes
In a scroll compressor, one scroll is stationary and the other______ Refrigerant enters the ______scrolls at the
and leaves at the center.
orbits; outer edge
The amount of compression in a centrifugal compressor depends on the______ the impeller which depends in turn on the impeller’s________and rate of rotation.
tip speed of; diameter
In reverse hydrostatic sealing the flow of____ across the seal opposes the flow of____ across the bearing.
refrigerant vapor, oil
In multistage centrifugal compressors, thrust loads are reduced by
Opposing impellers
The purpose of a purge system on a condenser is to eliminate_____ from the refrigeration system.
Air
Reducing a compressor’s capacity by closing pre-rotation vanes raises the pressure in the system’s_____
Evaporator
Which of the following is an important factor to consider when selecting a motor to run a refrigeration compressor?
Horsepower rating
Which of the following motors can be used in hermetic compressors?
Capacitor-start, induction-run
You can reverse the direction of a single-phase induction motor by
reversing the connection of either the starting or running winding
To change a dual-voltage motor to run on 240 V inslead of 120 V, you need to
connect the two running windings in series
A single-phase motor used in a hermetic compressor has a relay to disconnect the starting winding from the circuit when the motor approaches its running speed One kind of relay operates when the current in the______winding falls to a preset value Another kind operateswhen the voltage across the_____winding rises to a preset value
running; starting
The two basic categories of motor starting devices are
contactors and starters
A reduced vollage starter lirits the current to the motor at startup in order to prevent
voltage drops to other equipment
Overload protection for compressor motors may be provided by a(n)
external bimetallic disk
Crankcase heaters are especially useful on compressors that are subjected to
Cold climates
Installing a suction-line accumulator can protect a compressor from damage caused by
Slugging
The “first rule” of preventative maintenance for compressors and related components is to
follow the manufacturer’s recommended maintenance schedules and
procedures
Typical preventative maintenance procedures for compressors and related equipment include
listening for unusual noises
A compressor may overheat because of a(n)
Low oil level
When pumping down a compressor for service, run the compressor with the valve on the suction line closed, then close the valve on the discharge line and stop the compressor Repeat this process until the pressure holds at_____DSIg
+2 to +5
After disassembling a reciprocating compressor and cleaning the parts, you should inspect the parts for
excessive wear on bearing surfaces
The function of an evaporator is to_____
heat (from/to) the______
remove; material being cooled
The capacity of an evaporator is affected by the
cleanliness of the evaporator
A comfort cooler______the humidity of moist air by cooling the air to a temperature______the dew point.
reduces; below
Unlike a dry-expansion evaporator, refrigerant in a flooded evaporator enters as_____liquid and exits as______ vapor
All;part
A eutectic solution is a brine in which the concentration of sall is precisely set to achieve the lowest possible
Freezing point
Which evaporator arrangement offers the greatest flexibility?
Two evaporators in parallel, each with its own expansion valve
A cascade refrigeration system has more lhan one
compressor, evaporator, condenser, and refrigerant
The basic law(s) of thermodynamics that apply to refrigeration state that
heat flows from a warmer substance to a cooler substance
The net refrigeration effect can be increased by_____the refngerant.
Subcooling
Using a heat exchanger to lower the temperature in the liquid line and raise the temperature in the suction line has the advantage(s) of reducing
the amount of liquid refrigerant entering the compressor
The amount of oil entering an evaporator can be reduced by using a(n)
Oil separator
If the fluid being cooled by an evaporator circulates through the coil rather that moving slowly or not at all, the perfornance of the evaporator improves because of the
increased temperature difference across the wall of the evaporator
An evaporator can be defrosted by
reversing the flow of refrigerant
To remove rust, scale, and sludge from a shell-and tube evaporator you should use a(n)_____as necessary.
Brush
A water coil can be winterized by draining out the water and
leaving the coil dry for the winter
Frost buildup on an evaporator coil is increased by_____airflow and____ air
Low;humid
Bent fins reduce the cooling capacity of an evaporator, because they______
reduce the area exposed to the air
The purpose of the metering device in a refrigeration system is to
control the flow of refrigerant into the evaporator
In controlling the flow of refrigerant into a flooded evaporator, the float of a high-side float valve is located [at/on] the
high-pressure side of the valve port
If floodback occurs in a system using an AXV, a likely cause is
ice on the spring chamber above the diaphragm
A common problem with TXVs is ice in the valve port. The proper way to correct this problem is to____
replace the filter-drier
The operation of an AXV is controlled by the
pressure in the evaporator
In a secondary-refrigeration system, the refrigerant removes heat from the material to be cooled. This refrigerant then transfers heal to the ______
refrigerant In the process, that____
Secondary; primary
An ideal” refrigerent has which of the following charactenslics?
Nonflammable
A positive-displacement compressor uses a piston or other device to
compress refrigerant vapor in a chamber
Basic evaporator configurations depend on whether they have one or more tubes and whether or not they have
extended surface areas
Mulliple-circuit evaporators have headers or distributors that direct refrigerant to each coil from_____ expansion valve(s)
One
The capacity of a condenser is affected by the
area of contact with the cooling medium
Natural -draft air cooled condensers and forced-air condensers are alike in that both types
depend on air circulating over the coils
Low-ambient control in air-cooled condenser can be achieved by
closing the dampers
Spring-loaded relief valves protect a system against explosion by acting in response to high______Fusible plugs act in response to high______
pressure; temperature
Periodic maintenance of air-cooled condensers includes doing which of the following every three
months?
Checking all belts and pulleys
In the_____system, water passes through the condenser to cool the refrigerant. The water Is then_____
wastewater; discharged to the sewer
In a water-cooled condenser system, “makeup water” is used for
replacing water lost through evaporation
Tube- in-tube, shell-and-coil, and shell-and-tube condensers are alike in the following way(s):
liquid refrigerant collects at the bottom
A condenser has a pressure-relief device that______ if the refrigerant pressure becomes too high
releases refrigerant
Generally, how long should you allow a chemical cleaner to stand in a condenser?
A few hours
What type of cooling tower is shown in the drawing below?
Induced draft, counterflow
Which components in the water circulating system for a cooling lower or spray pond are used to keep the concentration of minerals low?
Bleedoff valve
The capacily of a cooling tower can be controlled by means of (a)
Diverting valve
As part of maintaining a cooling tower, you should check the_______ everyday
Float valve for clogging
Tho basic classifications for evaporative condensers are
blow through and draw-through
An evaporative condenser may include a desuperheating coil for the purpose of
reducing the formation of scale
Which of the following methods will maintain condensing pressure during cold weather operation?
circulating water intermittently
What will prevent the water in an evaporative condenser from freezing during cold weather?
Installing a sump heater
As a part of maintaining an evaporative condenser you should check the________
every three months.
fan blades for tightness
One of the main categories of water-related problems in an air-conditioning or reirigeration system is
Corrosion
Corrosion in a water-cooled system can be caused by
biological organisms
Scale formation can be reduced in a refrigeration system by adding______ to the cooling water
Acid
Bactera and algae can be controlled in a refrigeration system by adding_____ to the cooling water
Chlorine
Chemical detenoration in a wooden cooling tower can be controlled by
keeping the pH of circulating water in the 6.0 to 7.5 range
Which of the following can increase the capacity of a cooling tower or a spray pond by the greatest amount?
Increase in air velocity across the surface
In a cooling system, one of the main lines in the piping system is the_____line
liquid
Steel pipe is typically joined by means of
Flanges
Tubing is often preferred over piping in a cooling system, because it
absorbs vibration better
Refrigeration tubing is typically joined by
Soldering
The function of the discharge line in a refrigeration system is to
convey the refrigerant to the condenser
The “ontrainment” of compressor oil is the_____ The moving refrigerant
drawing in and transporting of oil with
In order to keep entrained oil droplets moving through the piping, the refrigerant must move at______fpm in horizontal piping and______fom in a vertical riser.
500 to 700; 750 to 1,500
Refrigerant can be prevented from pollecting in the compressor during the off cycle by installing a(n)______ in (on) the______
check valve: discharge line
Accossones often added to a discharge line include a(n)
discharge muffler
Subcooling is desirable in the liquid line, because it
reduces the volatility of the refrigerant
If the pressure in the liquid line drops, flash gas can form, which can reduce the
refrigerating effect
With halocarbon refrigerants, the movement of oil is beller in the liquid line than in the discharge line, because the
oil is miscible in most liquid refrigerants
A liguid receiver is used lo
store all the refrigerant during repairs
The purpose of a solenoid valve in the liquid line is to stop the flow of refrigerant to the
Evaporator
A double suction riser installed in a cooling system enables the system lo operate at maximum load without creating excessive_______in the suction line
Pressure drop
An accumulator in the suction line traps oil and liquid refrigerant to keep it from entering the_______A heater in the accumulator evaporates the_______
compressor; refrigerant
An evaporator pressure regulalor valve closes part way if the pressure at the evaporator outlet becomes too______ A crankcase-pressure regulator valve closes part way if pressure at the compressor inlet becomes too______
low; high
The suction line is insulated in order to prevent or reduce______the line
condensation on the outside of
The amount of od fat can build up in The suction line of an idlo single compressor system 15 much_______ than the amount hat cen build up m an idle comoressor of a multiple compressor system. To prevent damage from excessive oil buildup the suction lino should include a trap
win the minimum rise of______in
Less; 14
Piping problems that result in operating problems are often caused by
Liquid hammer
Which of the following expansion joints can be used in a refrigerant line?
Bellows
Which kind of support is appropriate for a horizontal piping run of 15 feet long?
Rod-type hanger
The problems caused by vibration in the piping of a cooling system include
damage to the valves and controls
Insulalion is needed on the liguid line if the line is_______ than its surroundings. The purpose of insulation on the liquid line is to prevent the loss of any_______ of the refrigerant
much colder; subcooling
When brazing tubing to a fitting, you should first heat the________ until the _______melts.
Fitting; flux
What is he main function of a control system?
Maintain a variable at a setpoint
Air conditioning and refrigeration systems are commonly controlled by_________control
Proportional
The power to operate a control system may come from
Fluid under pressure
An RTD responds to a change in temperature by undergoing a change in its
Electrical resistance
Relalive humidity is defined as the amount of moistore in the air
divided by the amount it can hold
In a pressure sensor that uses a Bourdon tube, changes in pressure are sensed by changes in the_______of the tube.
position of sealed end
An air-conditioning system has a two-position damper in the duct bringing outside air into the building and a second two-position damper in the return-air duct. When the system shuts down,
the outside air damper should be_______
and the return-air damper should be_______
Closed; open
Which of the following is an advantage of variable-speed drives over older methods a controlling the output of an air-conditioning of refigeraton system?
Proportional control can be used
Unlike floating control, the proportional control is
Continuous
The air supply for a pneumatic control system requires which of the following?
Drier
A PE relay is used to control a device operated by______
Electricity
Setting the gain of a controller determines how much a change in the______ affects the_________
controlled variable; controlled device
Adding integral action to a controller improves system performance by reducing_______. Adding derivative action improves performance by reducing_________.
offset; overshoot and undershoot
In pumpdown control, the compressor starts when the pressure________ in the_______
increases; suction lime
The high-pressure control in the discharge line of an air conditioning or refrigeration system responds to high pressure by _________
shutting down the compressor
A differential-pressure oil-safety control shuts off the compressor if the difference in pressure between the_________ and the oil pump ________ does not become high enough within a given time
compressor crankcase; discharge
In modulating the flow of water to hydronic terminals, the temperature control method has the
advantage of
preventing system freeze-up in cold weather
In setting up a preventive (PM) program, your first step should be to
inspect the system in detail
To maintain oil pressure in a 10-hp reciprocating compressor, a________ oil pump is used.
positive-displacement
To adjust the water regulating valve on a water cooled condenser, you should turn the adjusting screw until the_________ is at the design value You should make this adjustment when the equipment is running at _______ load
head pressure; maximum
The main requirements for maintaining a pneumatic control system include
removing and disassembling valves
The main requirements for maintaining an electric or electronic control system include
checking electrical contacts for pitting
Which of these control loops adjusts the setpoint automatically?
Reset system
What kind of capacity control is commonly used on large reciprocating compressors?
Cylinder unloading
What are the basic component of a control system ?
Sensor, controller, controlled device
