Air Conditioning and Refrigeration Engineering book gives you a simple reference to all parts of the point. This asset tends to the most present zones of intrigue, for example, computer-aided design and drafting, desiccant air conditioning and vitality preservation. It is an intensive and helpful manual for air conditioning and refrigeration engineering. Principles of Electromagnetics by Matthew N. Sadiku, S. Refrigeration and Air Conditioning Technology, 6th Edition, a time-honored best seller, has been updated and revised to provide superior hands-on information needed to successfully maintain and troubleshoot today's complex heating, air conditioning, and refrigeration systems.
The new sixth edition contains units updated to include advances or changes in technology, procedures,. Modern Refrigeration and Air Conditioning provides an excellent blend of theory with job-qualifying skills, making it a leader in the refrigeration and air conditioning field! This comprehensive text teaches both fundamental principles and the service techniques needed to diagnose and remedy HVAC problems. Modern Refrigeration and Air Conditioning contains the.
Refrigeration, Air Conditioning and Heat Pumps, Fifth Edition, provides a comprehensive introduction to the principles and practice of refrigeration. Clear and comprehensive, it is suitable for both trainee and professional HVAC engineers, with a straightforward approach that also helps inexperienced readers gain a comprehensive introduction to the fundamentals of the.
Focused on the food service industry, chapters address how HVAC technicians service medium- and low-temperature refrigeration equipment such as walk-ins, reach-ins, refrigerated cases, and ice machines. Readings also include. This text has been designed for students taking mechanics and technician courses at technical schools, colleges and other training institutions. This causes the defrost heater to remain on while in the cooling cycle. When this happens, the compressor runs continuously and the unit no longer cools.
In this case, the timer A. Knob Mount must be replaced. Electrical Terminals C. A device for automatically regulating the temperature inside a refrigeration unit by controlling the operation of the compressor. The manually adjustable control knob attached to its operating mechanism is mounted inside the cabinet, usually with two screws.
It consists of a gas-charged capillary tube called a sensing bulb connected to the operating mechanism. The sensing bulb is attached to the evaporator.
The operating mechanism of the thermostat responds to the pressures exerted from the trapped gas within the sensing bulb. As the temperature of the evaporator coil drops, the volume of gas decreases due to contraction , and thus the amount of pressure exerted upon the accordion-type bellows within the thermostat operating mechanism is reduced, causing the bellows to contract and open a set of contacts, disrupting the flow of current to the compressor motor.
As a result, the contacts are forced to close by the expanded bellows, restoring the flow of current to the compressor motor. On some freezer and refrigerator models, the sensing bulb is not attached to the evaporator, in which case, the temperature of the refrigerated air is transmitted to the operating mechanism.
Starting relay. Because starting a compressor requires more torque and draws at least three times the amperage of its normal running Current-type, speed, compressor motors are equipped with push-on-style starting relay a starting winding and a running winding and both compose the stator.
At the instant of starting, current flows through both windings. Since heavy wire is used in the starting winding, if it runs more than a few seconds, it will overheat and possibly burn. A starting relay is an electrical device that energizes the starting winding for a brief time. The starting relay plays an important role in the life of a compressor motor. Should the relay not disengage from energizing the starting winding, the starting winding in the compressor motor will burn, and the compressor will have to be replaced.
In household refrigeration units, they are installed under the compressor terminal cover and connected to the compressor start and run terminals. Some relays come with three openings that connect the starting relay to the three terminals of the compressor. Many GE units are of this type. Figure 13 Overload protector. It is installed under the compressor terminal cover. Plastic cover with the common terminal of the 2. Discharge line compressor. Suction line Compressor.
The compressor is the heart of the refrigeration unit. It is a motor-operated device that circulates refrigerant much as a pump would in a sealed system. All household and many commercial refrigeration units employ hermetic compressors. This means that the compressor with its motor are sealed in an airtight canister as opposed to belt-driven compressors. When energized, it creates enough pressure difference to circulate the confined refrigerant in the entire sealed system.
Through the compressor suction side, vapor refrigerant in the evaporator is drawn in and changed to hot vapor by compression. It is then forced into the condenser through the compressor discharge tube where it is cooled to its liquid state again before reaching the evaporator. An efficient compressor must be able to remove the refrigerant vapor at the same rate that liquid refrigerant enters the evaporator and vaporizes.
The low-pressure side of the compressor is connected to a tubing having a larger diameter than that of the high-pressure side. These pressures are checked by installing access valves such as piercing valves on the copper tubing on the suction and discharge lines of the compressor see fig.
The installation of piercing valves mainly applies to the residential units as compressors used in most commercial systems are equipped with service valves see figs. Many Company Courtesy of Henry Valve refrigeration problems can be diagnosed simply by checking the compressor discharge and suction pressures. A cylinder made of copper or brass of varying sizes depending on the capacity of the unit filled with alumina or silica gel. Its function is to remove moisture that penetrates the sealed system by absorption.
It is installed at the inlet of the capillary tube. The ends are either silver brazed or coupled by flare connections. In the sealed system, only pure refrigerant and a small amount of clean refrigerant oil should be circulated. Any moisture penetrating the system will cause a lot of trouble. The air in the atmosphere can penetrate the sealed system through very tiny pinhole leaks in the tubing or at the joints. Air contains moisture. When it enters the system, the excessive low temperatures cause the moisture to freeze and block the circulation.
Hence, the reason for the installation of filter-driers. Since the narrowest passage through which refrigerant moves is the capillary tube, this is the most likely place for the restriction. When a restriction occurs, the unit will no longer cool. When a sealed system is opened, moisture gets in and the filter-drier must be replaced prior to evacuating the system with a vacuum pump and recharging the unit with refrigerant.
The drier should be installed as close to the capillary tube as possible. Always keep the drier sealed until installed. If left open, it will absorb moisture from the air and very soon become saturated. In a properly operating system, the filter-drier should feel slightly warmer to the touch than the ambient temperature. These are the pipes through which refrigerant is circulated throughout the system. The tubing used in household units is made of copper.
Aluminum and steel are seldom used. Copper is relatively soft, flexible, and easy to bend and flare. Handle the tubing with care to prevent damage. Defrost bimetal. Also known as a termination switch or defrost thermostat. Not to be confused with the cold-control thermostat discussed earlier. A defrost thermostat is wired in series with the electric heater. It is clipped to the evaporator. No later than thirty minutes after the beginning of the defrost cycle, the timer takes the unit into the cooling cycle—at which time the operation of the compressor and the evaporator fan is restored—and the electrical circuit to the heater is opened.
Defrost bimetals play a very important role as the second component to control the defrost heater. If the heater is not de-energized, the excessive heat can cause damage to the unit. If it is not energized, the unit will no longer defrost. Often a bad defrost bimetal is mistaken for a bad defrost heater. The compressor draws in low-pressure, cool refrigerant vapor from the evaporator. This cool vapor is compressed squeezed and changed to hot vapor within the compressor, and then forced into the condenser.
In the condenser, heat from the refrigerant is radiated into the surrounding air, causing the refrigerant to return to liquid. While a residential refrigeration unit is running, the temperature of the condenser should feel well above room temperature when touched. For optimum efficiency, the condenser should be cleaned every year. There are two types of condensers commonly employed in residential units: static and fan-forced convection.
The static type is mounted on the back of the freezers and refrigerators. It radiates heat through natural convection without the use of a fan. As air in contact with the condenser tubing or fins absorbs heat from the hot refrigerant and becomes heated, it expands and rises, and cooler air occupies its space see fig. The fan-forced type is mounted beneath the unit. When the compressor operates, a fan moves air through the condenser tubing fins see fig.
Linted condensers should be cleaned regularly to prevent any restriction of air circulation. Consequently, the evaporator will no longer cool, the unit runs continually, the temperature never drops to a point low enough to satisfy the cold control, and the high-side pressure rises higher than normal, causing the compressor to burn out. Be sure that enough clearance is always provided for proper air circulation. When liquid refrigerant reaches the evaporator, it vaporizes or boils and absorbs heat from the freezer.
Sometimes the evaporator is referred to as a cooling coil. Due to the compressor suction power on the outlet of the evaporator and the fact that the capillary tube with its very small inside diameter is placed on the inlet side of the evaporator, the pressure in the evaporator is reduced to an average of 3. It is these low pressures that cause the refrigerant to boil and absorb the surrounding heat during its change of state essentials 1 and 3.
A Simple Flat-Type These fan-forced-type evaporators are used Evaporator in frost-free refrigerators and freezers. Four of the most common types of evaporators are illustrated above and in figures 3, 4, and 5. Figure 5 shows the cycle-defrost type of evaporator. This is basically a flat aluminum plate with a cooling coil in it. About three-fourth of this plate is in the freezer compartment while the remainder extends into the fresh-food compartment.
Since fewer loops of the coil are in the fresh-food compartment, only a small portion of the cold air is produced there but adequate to maintain the proper temperature.
This type of evaporator cools the refrigerator cabinet or freezer very rapidly. Manual-defrost refrigerators have a shell-type evaporator, which is located in the top of the cabinet. The shell type is similar to the evaporators used in the cycle-defrost type, which is a flat plate, but bent into a boxlike configuration see fig.
Frozen food and ice trays are kept inside the shell while the fresh food in the rest of the cabinet is kept at the proper temperature by the cold air emitted from it. Shell-type evaporators are almost always found in small office-type or inexpensive refrigerators. Normally, as a safety measure, an accumulator is installed at the outlet of all evaporators the small cylinder in fig.
It prevents liquid refrigerant from getting into the compressor, causing serious damage. This can be evidenced by a loud knocking when the compressor runs. The liquid refrigerant trapped there will get a chance to vaporize before entering the compressor. Capillary tube. A length of thin tubing connected to the high-pressure side liquid line from its inlet side and to the low-pressure side of the system the evaporator from its outlet side.
Liquid refrigerant is forced to flow through the capillary tube by these two forces. Because of the small inside diameter of the capillary tube, a constriction in the flow of refrigerant is created in the sealed system. This constriction maintains the pressure difference between the high and low side. Without continually maintaining this pressure difference, the vaporization and liquification of the refrigerant would not be possible. When refrigerant reaches the larger space of the evaporator by the suction power of the compressor , the low pressures in this environment immediately cause the refrigerant to vaporize and absorb the heat from the evaporator.
If a capillary tube must be replaced for any reason such as a restriction that cannot be cleared with a tube cleaner , it is most important to replace it with one of exactly the same length and inside diameter. The diameter is measured by a capillary tube sizing kit. Capillary tubes are used in different sizes and lengths according to the capacity of the unit see fig.
Defrost heater. It is an electric resistant heating element clipped to the evaporator in frost-free refrigerators and freezers. The purpose of the defrost heater is to melt the frost accumulated on the evaporator surface during the run cycle.
At this point, a termination bimetal senses the rise in temperature and disrupts the flow of current to the defrost heater, even before the defrost cycle ends. In many models, a length of electrical resistance heating element is also installed on the inlet of the drainpipe. It is energized during the defrost cycle to prevent condensation from the evaporator from freezing and blocking the flow down the drain tube.
In cycle-defrost refrigerators, an electric resistant heating element wired in series with the compressor is clipped to the inlet and outlet tubing of the fresh-food evaporator to defrost the frozen food evaporator during the off cycles see fig. The heater is energized when the temperature control is satisfied.
Evaporator fan. In frost-free refrigerators and freezers, a fan is installed over the evaporator to move air through the evaporator and circulate it in the freezer and the fresh-food compartments.
The pattern of air Various parts courtesy of Marvel Industries, Division of Northland Corporation on the evaporator coil. Consequently, frost will B. A condenser fan motor build up on the coil. A commercial double freezer compartment s h a f t fa n m o to r. As a obtained separately. The same thing happens in air conditioners. If the evaporator blower fails, air will no longer be circulated through the cold evaporator fins, causing an accumulation of ice on the evaporator plate, and a sudden temperature rise in the air-conditioned area.
Condenser fan. In automatic-defrost freezers and refrigerators and in larger-capacity units that require a more rapid cooling of the condenser, additional air movement through the condenser is provided by a fan called forced draft cooling.
Air is drawn into the compressor compartment from one side of the front grille, circulated through the condenser, and expelled through the other side of the front grille. In some side-by-side models, air is expelled at the rear of the compressor compartment. In addition to the rapid cooling of the condenser, the condenser fan also causes rapid evaporation of water in the condensation tray.
The hot refrigerant causes the accumulation of frost on the evaporator coil to melt. What are the primary parts of a refrigeration unit? Where is the evaporator located? What is a sealed system? What is the function of an evaporator? What is the primary function of a defrost timer? What are the most common troubles with defrost timers? What happens when loose connections on a defrost timer fuse together? What is the primary function of a thermostat? What is a thermostat sensing bulb, and where is it attached?
What purpose does an overload protector serve? Where is an overload protector located? What is the role of a starting relay? Which compressor winding s is are are energized at the instant a compressor starts? How many windings are there in a compressor?
What is the suction port of a compressor connected to? How are the pressures in a sealed system checked? What is the primary purpose of a filter-drier? What are other names for a defrost bimetal? What is the primary purpose of a termination switch? What is the defrost bimetal clipped to? How many types of condensers are used in residential refrigeration? How many types of evaporators are there? Where is an accumulator installed? What is the primary function of a capillary tube?
What is the most important thing to consider before replacing a capillary tube? How many types of defrost systems are there? What are the most common types of condensers used in residential refrigerators and freezers? What is the purpose of insulating materials in refrigerator walls? How is airflow regulated in a side-by-side refrigerator? What is the principal difference between a refrigerator and a freezer? What components are activated in opening the flow of hot gas in a hot gas defrost system?
Why is fan-forced circulation used in frost-free refrigeration? What is the capillary tube connected to? What is the function of an accumulator? It includes flaring, brazing, swaging, bending, and cutting tubing. Silver brazing: Brazed joints are very strong and considered to be the best method of making Figure 17 leakproof connections. Clean and burnish the joints with fine sandpaper. The parts to be brazed must be fitted snugly and Figure 18 accurately, clean, and securely supported so that no part can move during brazing.
Apply the recommended flux fig. Be sure the joint is firmly supported to avoid movement during brazing or cooling. Heat the joint evenly with a torch figs. More heat will be hacksaw to cut tubing. Start heating Figure 19 about one-half inch to one inch away from the joint. Never hold the torch in one spot.
Keep it moving until the joint turns cherry red. Apply the brazing alloy at the top and allow it to seep into the heated joint. Since alloy always flows toward heat, hold the torch at 1.
Teflon Tape the back of the joint to let the alloy flow into 2. Flux the joint and fill it up. Brazing Rods 4. Inspection Mirror 5. Cool the joint with a piece of wet rag, then use hot water and a brush to clean it. If the brazing alloy contains any amount of cadmium, do not inhale the fumes or allow them to come in contact with your eyes or skin.
Swaging copper tubing. Swaging is a process Figure 20 by which the end of one tube is enlarged to allow the end of another tube of the same diameter to fit inside for brazing.
This method of joining two lines of the same diameter eliminates the use of fittings. As a general rule, the length of the swaging, or overlap, should equal the outside diameter of the tubing being joined.
For instance, when joining one-half-inch tubing, the swaged overlap should be one-half inch; for three-fourth-inch tubing, the length of the swage should be three-fourth-inch, etc.
Figure 22 illustrates two pieces of tubing where one has been swaged to create a connection with the other. There are two types of swaging tools available: the lever type and the more popular punch type fig. Different sized collars and punches Heat tubing with Figure 21 the yellow flame. To use the punch type, insert Correct Brazing Technique for the tubing in the correct size hole in the Joining Copper Tubing anvil block.
Select the proper size punch 1. Use fine sandpaper to clean the joint and insert it in the tubing. Hammer it before applying flux.
Heat tubing starting one-half inch to one inch from the joint. Move torch toward joint and heat that area briefly. Concentrate heat a little above the joint until joint turns cherry red and apply flux around joint.
It is easy to take brazed joints apart using the same method by which they were joined. Heat the joint with a torch until it becomes cherry red in color, and then grab the tubing near the joint with a pair of pliers and pull it apart.
Before removing the old part, you can use this method to disconnect the tubing. To do this, use an access valve. Refer to figs. Insert the punch in the end of the tubing and hammer it down until the desired expansion Figure 22a is obtained. A typical brazing outfit: acetylene and oxygen tanks, pressure gauge, acetylene-regulating valve and torch. Above, a service valve wrench. Instead of connecting tubing by swaging before brazing, special couplings can be used to join tubing of similar or different sizes by silver brazing.
Figure 24 illustrates some of these couplings. They are available in most tubing sizes. Reduction 3 and Straight with stop 5. Straight without stop 6, 7, and 9. Tee 10, 11, and This is a metal-to-metal connection without the use of a solder. To create a flared connection, the ends of the tubing to be joined should be cut straight and square with a tubing cutter fig.
To do this, the tubing must be held securely while cutting. Use a small vice, C-clamps or Vice-Grip pliers. Then ream the inside of the cut to make it smooth.
Most tubing cutters have a reamer attached. When using either method, make sure that no chips or shavings remain inside the tubing. Flaring couplings. The flared fitting relies on the airtight connections of the fittings rather than brazing. The fittings are a flared half union coupling and two female flare nuts. They are retained on the tubing by a small flaring on each of the ends to be joined. For this type of connection, a different set of tools is needed from those used in making a brazed connection.
They are inexpensive and available almost everywhere in hardware and refrigeration supply stores. Cut and clean the ends of the tubes as described earlier. Use a fine- toothed file to smooth the ends or to make a slight correction if the tubing is not cut perfectly square.
Place a female flare nut on each of the tubes with the larger end facing the cuts. Do this prior to making the flare because the nut will not slide over the end after the flare is made.
Slide the nuts back on the tubes to provide enough working room. Then put the end of the first tube into the flaring block hole with the same diameter as the tube. The end of the tube should extend slightly above the chamfered end of the hole to allow enough metal to form a satisfactory flare.
The tools have directions with them for guidance in this step. As a rule of thumb, the extension above the block should be about one-third of the height of the flaring. Put a drop of refrigerant oil on the bottom of the flaring cone where it comes in contact with the tubing. Tighten the spinner until the flare is formed. Avoid overtightening as this will thin out the wall of the tube and weaken the flare.
In most cases, after the spinner touches the tubing, about six and a half turns should form the flare. Do the same with the other piece of tubing that is to be joined.
Use Pipetite a pipe-fitting compound or a short length of Teflon tape around the male threads to establish an airtight seal. Teflon is the better of the two. If the compound is used, be sure to apply it sparingly to prevent it from getting into the lines when the flare nuts are connected. NOTE: Connections made in plastic tubing [such as a water supply to an ice maker] use compression-type fittings since plastic cannot be flared.
Put nut on tubing and insert tubing into correct size collar in anvil block. Turn spinner about six and a half turns. Figure 26 3. Remove spinner and tubing from anvil block. Tubing can now be connected to a male counterpart.
Use Teflon tape to ensure an airtight seal. A variety of compression fittings used in refrigeration and air-conditioning. To prevent possible leaks, do Figure 26a not overtighten nuts and couplings. Unless the tubing is supported around its circumference, it will flatten at the bend and possibly crack, causing it to leak.
Use a tool called a bending spring shown here in figure 27 on the right. The bending springs are inexpensive and do the job properly. Place the spring over the tubing at the area to be bent, then bend it slowly and carefully, making a curve as large as practical. Do it in short stages until the appropriate curve is made. Remove the spring by twisting while sliding it off. For tubing larger than one-half inch in diameter, a bending lever with a flange attached to the end is used.
See illustration below. Figure 27a Spring-type benders upper right make it easy to form bends by hand without collapsing the tubing. They can also be used to protect tubing during installation and repair procedures.
The special coil spring wire easily slips over the outside of the tubing, and the belled end simplifies insertion and removal. The lever-type tubing benders illustrated on the left are used for the larger sizes of tubing as they require considerably more effort to bend.
The curved radius on the stationary bar has a scale in degrees. When the movable lever bends the tubing, its index mark indicates the degree of the curve. What method is used to bend larger diameter tubing?
Generally, how many half turns of the spinner should be sufficient to form a flare? Name 4 different types of flare unions. What are the most commonly practiced ways of joining tubing?
How should the torch be positioned while silver brazing? When applying heat to a joint, how is it determined when to apply the silver solder? What steps should be taken after a joint is silver-brazed? When should flux be applied to the joint? At what temperature does silver alloy melt? How is refrigeration tubing normally cut? What kind of coupling is used to braze tubes of the same diameter?
How and why should a silver-brazed joint be cleaned? What is the general rule to determine the overlap length when swaging copper tubing?
What is the purpose of punches with different sized diameters? How is tubing bent with a spring-type bender? What should be done before applying heat to the tubing? What is used when more heat is required for brazing larger-diameter tubing? How is a brazed joint disassembled? In what direction does alloy flow while it is being heated? This knowledge, coupled with the information on the troubleshooting charts, provides a quick diagnosis of the most common problems encountered in this career field.
Some of these compressors, used commercially, could be belt-driven or hermetic. The hermetic type has its motor and compressor coupled directly together in a sealed airtight metal housing, whereas the others are powered with a separately mounted motor and driven with a V belt s and pulleys. All residential and many light commercial refrigeration units are operated with hermetically sealed motors and compressors because they are compact and require little space.
In heavy commercial and industrial use, where large capacity units are required and space is not a problem, the separately mounted motors with v-belts and pulleys to drive the compressors work well. A reciprocating compressor is similar to an automotive engine with a piston moving up and down in a cylinder. Instead of relying on exploding and expanding gas to drive the piston, the piston is powered by an electric motor. As the piston moves downward or backward , the inlet valve opens and vapor is drawn in from the evaporator.
When the piston starts up toward the top or forward , the inlet valve closes and the gas is compressed thereby raising its temperature. Before the piston reaches the top or its most forward position , the discharge valve opens and allows the gas to be propelled into the condenser see fig. They are used in commercial and residential units, light and heavy applications. These compressors can be hermetic or externally driven.
As the piston moves upward, the vapor is compressed and converted to a hot gas, which is then forced into the condenser fig. In a reciprocating hermetic compressor, the circular motion of the rotor causes a back-and-forth movement of the piston. Right: A motor stator, B motor rotor, C compressor cylinder, D compressor piston, E connecting rod, F compressor winding, G compressor terminals under a plastic cover, H compressor housing weld, I compressor suction tube, J compressor discharge tube, K compressor housing.
It can be hermetically sealed or rely on an external conventional electric motor. They are used in commercial and residential units. As the rotor revolves inside the cylinder on an eccentric cam, the spring-loaded vanes pass the intake and discharge ports. As one vane passes the intake port, suction begins and cold vapor is drawn into the cylinder.
As the rotor continues its turn, the gas is compressed. When the other vane clears the discharge port, the gas is propelled through the high-pressure line into the condenser. It is then forced into the condenser. Rotary compressors are very susceptible to liquid refrigerant. As a safety measure, they are equipped with an accumulator on the suction inlet to prevent any unvaporized refrigerant from getting into the compressor motor.
Courtesy of Tecumseh Products Company In a rotary hermetic compressor, the circular motion of the motor rotor in the top causes the rotary compressor in the bottom to turn. A motor rotor, B motor stator C rotary compressor, D compressor terminals, E accumulator, F motor winding, G compressor discharge connection, H compressor suction connection.
As the impeller turns, a vacuum is created at its center, causing cold vapor to be drawn in. It is then compressed and expelled into the discharge port through the sides caused by high rpm. These compressors can be hermetic or externally driven and are used commercially. A screw-type compressor is similar in operation to a turbocharger. It has two cylindrical vanes with deep, spiraling flutes that mesh together like gear teeth. The extremely high rpm of the vanes meshing into each other creates vacuum on one side and high pressures on the other, causing refrigerant vapor to be drawn in from the intake port , compressed, and forced out through the compressor discharge port.
Screw-type compressors are used in heavy commercial applications. Figure 31 Courtesy of Gates Rubber Company The high-pressure-side service valve is usually located on the receiver, and the low-pressure-side service valve is installed on the compressor suction inlet.
A quick way to determine the condition of a compressor is to check the wattage consumption of the unit. A worn-out compressor may be indicated by a wattage reading below its wattage rating. Connect the wattmeter to the compressor circuit to be measured as shown in the diagram.
Depress button E. At first the meter needle will fluctuate to the right; then, immediately, it deflects to the combined reading the compressor start and run windings both engaged. In a second or two, the needle will deflect to the wattage consumption of the run winding.
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