Refrigerator Troubleshooting Diagram

Archive for the ‘Air Conditioning’ Category

Gas Fired Chillers

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Chillers operate on natural gas or propane gas. See Fig. 17-2. Gas is used for the major job of cooling. Electricity is used for the smaller energy requirements of fans, motors, and controls. This means electrical power requirements are only about 20 percent of those of a completely electrical unit.

Gas units are available in 3-, 4-, and 5-ton capacities. They use heat as a catalyst. They have no compressor. This means they have fewer moving parts than other types of systems. They are designed for outside installation. They cool by circulating, the refrigerant, which is plain tap water, through a matching coil. The coil is added to a new or existing furnace in the house. As the chilled water produced by the unit circulates through the coil, it absorbs heat from the conditioned space. The water, bearing the absorbed heat, is then returned to the unit outdoors, where the heat is dissipated to the outside air. Table 17-1 shows the amount of permanent antifreeze required when the outside temperature is below freezing. A defoaming agent also must be added.

Table 17-2 shows the specifications of Arkla 3-, 4-, and 5-ton units. Note that the refrigerant is R-717 (ammonia). Also, note the amount of gas needed to produce 3 tons of air conditioning—79,000 Btu.

Gas-fired units may be connected in 5-ton multiples to provide up to 30 tons of air conditioning. Figure 17-3 shows how they are doubled up to provide 10 tons. For some units, it takes 250,000 Btu of gas input per hour to provide 120,000 Btu/h of cooling. That means 48 percent efficiency, if the electrical energy needed is not accounted for in the figuring. For the unit referred to, the operating voltage is 230 V, with 60-Hz, single-phase operation. Wiring size is not too large, since there is a maximum of 8 A drawn for the condenser fan motors and 33 A for the solution pumps. Normal running current for the solution pump motors is only 5 A. Locked rotor current of 33 A occurs only if the motor is stuck or jammed so it cannot start. The start currents may also reach this 33-A level under some load conditions.

The chilled water system uses stainless steel to prevent problems with rust and other ferrous metal piping problems. There is only one electrical, one gas, and one chilled water supply and return connection for each unit.

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February 7th, 2011 at 8:37 am

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Ammonia Refrigerant in a Gas-Fired System

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Ammonia is also used as a refrigerant in a gas-fired system. As the ammonia is moved through the system, it changes state becoming strong and weak vapor and a liquid. Chilled water is used as a circulation coolant. Very few electrical pumps are needed. Fans are still needed to remove the collected heat. A pump is needed for circulating the ammonia. A pump is needed for circulating the chilled water.

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February 7th, 2011 at 8:32 am

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Absorption Cooling Cycle

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The absorption type of air-conditioning equipment works on two basic principles: a salt solution absorbs water vapor and the evaporation of water causes cooling. In this particular discussion, the absorption cooling cycle is appropriate since it is used in gas-fired air conditioners.

Most gas-fueled air-conditioning equipment use a solution of lithium bromide (LiBr) in water. Lithium bromide is a colorless, salt like compound that dissolves in water, even to a greater extent than does common salt.

A solution of lithium bromide and water can absorb still more water. Note that, in Fig. 17-1, a tank of absorbing solution (tank B) is connected with a tank of water (tank A). The air in the system is almost completely evacuated. The partial vacuum aids the evaporation process. Water vapor is drawn from the evaporator to the absorber. Evaporation of the water in the evaporator causes the water remaining in it to cool about 10°F (5.5°C). The evaporator effect in the evaporator is greatly hastened if the water is sprayed through several shower-bath sprinkler heads. A coil of pipe through which a material such as water passes can be placed within the shower of evaporating water. The water entering the coil of pipe at 55°F (12.8°C) will be cooled to about 45°F (7.2°C).

Since the absorber (B), shown in Fig. 17-1, continually receives water, it would soon overflow if the excess water that comes to it as water vapor was not removed. To avoid overflow, the solution that has absorbed water is pumped to a generator (C).

In the generator, the solution is heated directly by a natural gas flame. A steam coil may heat it indirectly. The steam is made in a gas-fueled boiler.

When the solution is heated, some of the water evaporates and passes into the condenser (D). The concentrated solution, that remains is sprayed back into the absorber (B). Here, it again absorbs water vapor that comes from the evaporator.

Water vapor in the condenser (D) is cooled by a separate coil of pipe through which water passes. The condensed water is returned to the evaporator (A).

Careful engineering is needed to make the system work well and economically. Attention must be given to temperatures, pressures, and heat transfer in all parts of the system. Practical machines with very few moving parts have now been developed.

Absorption units may also use ammonia as the refrigerant. In such system, heat from natural gas is used to boil an ammonia-water solution. The operation of the lithium-bromide cycle discussed earlier generally applies. In a system using ammonia, the temperature of the evaporator can go below the freezing point of water. Ammonia is referred to as R-717.

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February 7th, 2011 at 8:29 am

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Gas Air Conditioning

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There are three main types of gas air-conditioning cycles used today: compression, absorption, and dehumidification.

In both compression and absorption cycles, air temperature and humidity are tailored to meet variations in surrounding air conditions and changes in room occupancy. Both of these cycles evaporate and condense a refrigerant. They require energy for operation. Mechanical energy is used in the compression type. Heat energy is used in the absorption type. The dehumidification cycle is used primarily in industrial and commercial applications. Dehumidification reduces the moisture content of the air.

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February 7th, 2011 at 8:24 am

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Console Type Air Conditioning System

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The console air conditioner is a self-contained unit. These units come in 2- to 10-hp sizes. They are used in small commercial buildings, restaurants, stores, and banks. They may be water cooled or air cooled.

Figure 16-19 shows an air-cooled console air conditioner. You should be able to vent to the outside the hot air produced by the compressor and the condenser.

There are also water-cooled console air conditioners. They will require connections to the local water supply as well as a water drain and condensate drain. See Fig. 16-20. Note the location of the parts in Fig. 16-19. Water is used to cool the compressor. In both models, the evaporator coil is mounted in the top of the unit. See Fig. 16-21. Air blown through the evaporator is cooled and directed to the space to be conditioned. In some areas, a water-cooled model is not feasible.

Since the evaporator coil also traps moisture from the air, this condensate must be drained. This dehumidifying action accounts for large amounts of water on humid days. If outside air is brought in, the condensate will be more visible than if inside air is recirculated.

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February 7th, 2011 at 8:22 am

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Chilled Water Air Conditioning

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To produce air conditioning for large areas, such as department stores and office buildings, it is necessary to use another means of cooling the air. Chilled water is used to produce the cooling needed to reduce the interior temperature of offices and stores. To understand the function of the chilled water, it is necessary to look at the total system. See Fig. 16-14.

The refrigerating machine is the chiller. Water is supplied to the chiller. There, its temperature is reduced to about 48°F (8.9°C). The chilled water then flows to the coils in the fan coil unit. The fan coil unit is located in the space to be conditioned. In some cases, a central air-handling system is used. Pumps are used to move the water between the chiller and the air-handling equipment. The water is heated by the room air that is pulled over the chilled water coils. Thus, the water reaches a temperature of about 55°F (12.8°C). In some installations it reaches 58°F (14.4°C). The water absorbs about 10°F (5.5°C) of heat as it is exposed to the room air being drawn into the unit by blowers.

The heated water is then pumped back to the chiller. There, the water is chilled again by the machine removing the absorbed heat. Once chilled, the 48°F (8.9°C) water is again ready to be pumped back to the fan coil unit or the central air-handling system. This process of recirculation is repeated as needed to reduce the temperature of the space being conditioned.

Figure 16-15 shows the refrigeration cycle of a chiller.

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February 7th, 2011 at 8:16 am

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Absorption Type Air Conditioning Systems

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A boiling refrigerant in an evaporator absorbs heat. The evaporator pressure must be low for boiling to take place. To produce the low pressure, it is necessary to remove the refrigerant as soon as the boiling refrigerant vaporizes. Vapors can be absorbed quickly by another liquid. However, the other liquid must be able to absorb the vapor when it is cool. It will then release the absorbed heat when it is heated.

Ammonia is one of the refrigerants most commonly used in the absorption-type air-conditioning systems. Ammonia vapors are absorbed quickly by large amounts of cool water. In fact, it can absorb vapor as quickly as a compressor.

High-pressure ammonia can be fed as a pure liquid through a metering device directly into an evaporator. See Fig. 16-11. Refrigeration takes place until the highside liquid ammonia is exhausted or the water in the absorber tank is saturated. Once saturated, it no longer absorbs ammonia. If the ammonia tank and the absorber are large enough, these components can be used as part of an air-conditioning system.

A system can be devised to handle large installations. See Fig. 16-12. In this system, some of the ammonia is removed from the water. This leaves a weak water solution of ammonia. This solution flows by gravity to the absorber.

The water in the absorber absorbs the ammonia. Such absorption continues until ammonia represents 30 percent of the water-ammonia solution.

Such a strong (30 percent) solution of ammonia is called strong aqua. Aqua means water. The strong aqua is pumped up to the generator. The absorber operates at low-side evaporator pressure. That is why the pump is necessary. The generator has a high-side pressure.

Air is driven out of water by heat. Ammonia also can be driven out of water by applying heat. The high temperature ammonia vapor rises and moves to the condenser. Weak condensed liquid flows back to the absorber through the force of gravity. In the condenser, the latent heat is removed from the ammonia vapor. Condensed ammonia liquid flows through the liquid receiver to the evaporator. In the evaporator, the ammonia boils at reduced pressure. Latent heat is absorbed. The liquid ammonia changes into a vapor. In changing to a vapor, the ammonia produces refrigeration. Ammonia is only one refrigerant used for this type of system. Lithium bromide and water also can be made into a refrigerant. Figure 16-13 shows a typical absorber system. Several manufacturers make packaged units for absorber systems.

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February 7th, 2011 at 8:10 am

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Evaporative Cooling System

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In some locations, it is possible to use the cooling tower principles to condense the refrigerant. This method has the usual problems with water and tower fungi.

The condensing coil is cooled by air drawn in from outside the tower and forced upward over the coil. Water is pumped continuously to a distribution system and sprayed so that it drops in small droplets over the condensing coil. See Fig. 16-10. The water is reused since it cools as it drops through the moving air stream. In some systems the water is pumped up and into a trough. The water drips down over the condenser coils and cools them.

In some cases, the water moves through the tubes that surround the refrigerant-carrying tubes. The air stream then removes the heat and discharges it into the surrounding air. This means the cooling tower should be mounted outside a building. In some instances it is possible to mount the tower inside. However, a duct is then needed to carry the discharged air outside. As shown in Fig. 16-10B, the water is carried off and must be replaced as it, too, evaporates. The pan is filled to level when the float moves down and allows the water makeup valve to open. If the condenser temperature reaches or exceeds 100°F (37.8°C), the thermostat turns on the water and the fan.

Problems with this system center in the electrical control system and the water system. The controls, fan motor, and pump motor are electrically operated. Thus, troubleshooting involves the usual electrical-circuit checks.

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February 7th, 2011 at 7:53 am

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Direct Multizone Air Conditioning System

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The direct multizone system unit is roof mounted and can be used for cooling and heating. See Fig. 16-6. It can use chilled water for cooling up to 550,000 Btu/h.

Air distribution is 12- or 16-zone multizone control at the unit or double duct with independent mixing dampers at each zone. Figure 16-7 shows the typical applications of such a unit with a zone distribution system using mixing dampers located at the unit. A double duct distribution system with zone damper boxes can be used. Mixing dampers are remote from the unit. The net weight of the unit is 2525 lb or 11/4 tons.

Figure 16-8 shows the location of the parts inside the unit. Figure 16-9 shows how the refrigerant piping is laid out for the unit when two compressors are used for cooling purposes. Note that this unit uses an accumulator. There are certain conditions under which the capacity of such a unit must be rated. These conditions are the temperature of the evaporator air, the condenser coil air temperature, the speed of the blower motor, and its volume of air delivered.

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February 7th, 2011 at 7:49 am

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Commercial Air-Conditioning Systems Maintenance

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Before performing any maintenance on the unit, make sure the main line switch is open or in the OFF position. Label the switch so that someone will not turn it on while you are working.

The components should be checked and serviced as follows:

• Blower motor oil. According to the manufacturer’s recommendations, the rating plate will usually give lubrication instructions.

• Electrical connections. The electrical connections should be checked periodically and retightened.

• Pulley alignment and belt tension. Check the blower and motor pulley for alignment. Also check the belt for proper tension. It should have approximately 1 in. of sag under normal finger pressure.

• Blower bearings. Blowers are equipped with prelubricated bearings and need no lubrication. If, however, there are a blower unit and blower motor without sealed bearings, a few drops of oil must be added occasionally.

• Condenser and evaporator coils. Coils should be inspected occasionally and cleaned as necessary. Be careful not to bend the soft aluminum fins.

• Filters. System air filters should be inspected every two months for clogging because of dirt. When necessary, replace disposable-type filters.

Special Instructions
• Do not rapid-cycle the unit. Allow at least 5 min before turning on the unit after it has shut oil.

• If a general power failure occurs, the electrical power supply should be turned off at the unit disconnect switch until the electrical power supply has been restored.

• Air filters should be cleaned or replaced at regular intervals to ensure against restricted airflow across the cooling coil.

• During the off season, the main power supply may be left on or turned off. Leaving the power turned on will keep the compressor crankcase heaters energized.

• If power has been off during the winter, it must be turned on for at least 12 h before spring start-up of the unit. This allows the crankcase heaters to vaporize any liquid refrigerant that may be condensed in the compressor.

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February 7th, 2011 at 7:41 am

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