Refrigerator Troubleshooting Diagram

Mitsubishi AC MS-24NN Indoor Unit Schematic

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Mitsubishi AC MS-24NN Indoor Unit Wiring Diagram

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September 22nd, 2011 at 2:43 am

Mitsubishi AC MS-18NN Indoor Unit Schematic

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Mitsubishi AC MS-18NN Indoor Unit Wiring Diagram

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September 22nd, 2011 at 2:29 am

A/C Shell and Tube Condenser

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Shell and Tube Condenser

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September 13th, 2011 at 4:16 am

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Refrigerator Charging Cylinder

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When servicing certain appliances such as domestic refrigerators, window units, package units, ice machines, and automotive air conditioning, there cannot be any guess work as to how much refrigerant should be in the unit. There is a specific amount of refrigerant used in this type of equipment, and the manufacturer places that amount on the data plate. The amount needed in these units is usually given in pounds and ounces. When using small quantities such as this, one of the ways that it could be handled is with a very fine tuned scale or the charging cylinder. The cylinder is a valuable tool that should be a part of your tool inventory if you work on this type of equipment.

The operation of the charging cylinder is extremely easy once you understand the procedure. A tube where you place the amount of refrigerant is located in the center of the cylinder. On the outer perimeter is a plastic, movable, outer cylinder. At the top of the inner tube a valve and pressure gauge are located; and at the bottom there is a valve. Place a small amount of the refrigerant to be used into the cylinder through the lower valve. This small amount of liq­uid places pressure on the cylinder. A charging cylinder provides refrigerant in liquid form.

Read the amount of pressure on the gauge, rotate the outer cylinder until the proper refrigerant and pressure line up with the index. This outer, plastic, cylinder has graduations marked on it. These graduations are in ounces. Open the lower valve and allow liquid refrigerant to enter the inner tube, carefully observe the increments as the liquid column fills the center tube. When the proper amount of ounces is reached, close the lower valve. The exact amount of refrigerant needed to charge the specific system is enclosed in the center tube of the charging cylinder. Liquid refrigerant is dispensed from a refrigerant drum with the use of a valve labeled “liquid,” or by turning the drum upside down. Always allow a couple of ounces of refrigerant to purge your charging hose. Never break the vacuum of a good evacuation until the charging hose is purged of air and full of refrigerant.

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September 9th, 2011 at 8:02 am

Posted in Leak Testing

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Refrigerator Vacuum Pump

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The vacuum pump is another important tool, without which professional results are impossible. If a system is only open to atmospheric pressure for a short period of time, a method called purging the system is used. This method uses the refrigerant itself to displace any air that might be in the system. The refrigerant being heavier than air displaces air. If a system has been open to the atmosphere for a long time, purging will not be satisfactory. It is in this situation that an efficient vacuum pump must be used. Purging is the introduction of refrigerant through the suction side of the system, letting it exit at the high side of the compressor. The refrigerant should be allowed to flow long enough for the air within to be driven out by the refrigerant.

The service manifold and gauges are hooked to the vacuum pump by the center hose on the manifold. The low-side hose hooks to the low-side of the system, and the high-side hose to the high-side of the system. The system should not have any pressure in it when the vacuum pump is being hooked to it. Any pressure in the system can cause the removal of oil from the vacuum pump. The low-side gauge should show pressure dropping a short time after the pump pressure is 70 psi. If you look to the right side of the chart, you will see temperature scales in degrees F. The lines that fall from the left of the numbers are the reference lines. Looking down diagonally to the left until the line intersects the 70-psi line. You can see that this intersection takes place on the 40-degree line. This should be the actual temperature of the suction line at the compressor. This temperature is measured with a thermometer. If suction temperature is higher than the reading, refrigerant should be added. If suction temperature is lower than the reading, some of the charge should be removed from the unit. In Table 26-1 a graph chart is used. Another manufacturer uses a charging chart as shown in Table 26-2.

The charging by feel method is fast becoming a thing of the past. It can be done by a technician with a lot of experience with a specific in the system. The bad feature about the sight glass is that an inexperienced technician can overcharge a system trying to clear the bubbles or a flash from the sight glass. Those technicians learned incorrectly to charge a system until the sight glass is clear. If an ammeter was used during a load test, excess current would be apparent. If a system has’a restriction in its filter drier, bubbles or flashing can occur in the sight glass. If a heat load is placed on a system, and it is operating at a temperature higher than its design temperature, flashing in the sight glass will occur. Example: you are checking the condensing unit of a 40-foot by 60-foot by 15-foot walk-in cooler. The sight glass is flashing. Unbeknown to you, the local beer vendor is delivering his weekly order of beer to the store. With a case of beer holding the door open so that he may enter and leave with his handtruck uninhibited. The evaporator fans are pulling air from outside the conditioned space over them. The hot moist air is causing a heat load on the evaporator higher than it was designed for. You can see in the situation above that the unit will seem to be operating low on refrigerant; however, as soon as the door is closed and the unit operates as it was designed to do, the sight glass will clear. What would happen to the excessive amount of refrigerant in the system if it had been charged during the above example? The unit would be overcharged and eventually, damage and failure would occur. If an ammeter is used, and it reads maximum amperage for the unit, there is something else wrong with the unit besides a low refrigerant charge.

table-26-1

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September 6th, 2011 at 7:55 am

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Condensing Unit Leak Testing

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It is usually the condensing unit where a leak test begins. The reason is that at this unit, a leak is the easiest to find and repair. The most important tool the technician has is his eyes. Look very carefully for signs of oil. Small amounts of oil attract dirt which make it very visible. Care should be exercised when handling used oil. In certain cases when a compressor has had a burn out, remember that acid is formed and carried by the oil. Heavy concentrations of acid can damage the skin. In addition to your regular hand tools, a few extra specialty items are needed for leak testing.

A bottle of nitrogen will be essential in some leak testing situations. Remember the nitrogen regulator; never use this gas without the proper regulator. Electronic leak detectors are good in isolating an area of the leak. In certain cases where the concentration of refrigerant fumes is very high, the electronic leak detector may be over sensitive to the condition and thus unable to pin-point the leak. A halide leak detector is a must. The concentration of the leak will be indicated by the color of the flame. Difficulties in leak testing with the halide might be encountered on windy days. The wind might carry away the refrigerant fumes faster than the halide leak detector can pick it up. For this reason I recommend you have a six-foot by six-foot piece of construction plastic to use as a tent. On windy days the plastic is used to cover the entire condensing unit. With the addition of refrigerant pressure to the unit, one corner of the plastic is lifted and the hose of the halide leak detector is placed under the plastic. The hose sniffs for the refrigerant. A concentration of refrigerant fumes should occur now that the wind cannot dissipate the leaking refrigerant.

One of the biggest mistakes a technician makes when using the halide leak detector is to use too large a flame in the chimney. It is only necessary for the tip of the flame to touch the underside of the detector disc.

At times, leaks develop and only show at high pressure. This is one of the reasons that nitrogen is used. On the data plate of most air conditioning condensing units, the test pressure is marked. This pressure is applied to the unit in the factory to make sure there aren’t any leaks, defective joints, or materials. When applying nitrogen pressure, don’t exceed these limits. The operating pressure of the unit is lower than those ratings on the data plate. Nitrogen should be added to the system up to the pressure at which the refrigerant of that system would operate. With the addition of the nitrogen pressure, the high pressure leaks can be detected without having the unit operate. Another thing to remember is the pressure of the unit on a really hot day would cause the units pressure to operate at a higher pressure. You might be looking for a leak on a cool day, and the pressure would not be high enough to detect the leak.

A product called Leak Detector is on the market. It is similar to the bubble solution a child makes bubbles with. If you do not have this solution available to you, ordinary liquid soap detergent used in the home will suffice. When the halide or electronic leak detector localize the refrigerant leak, the bubbles of the solution will form at the exact location of a leak.

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September 6th, 2011 at 7:32 am

Posted in Leak Testing

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Double-Pipe Water-Cooled Condenser

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Double-pipe water-cooled condenser

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September 6th, 2011 at 3:42 am

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HVAC Air Cooled Condenser

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HVAC Air Cooled condenser

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September 6th, 2011 at 3:34 am

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Refrigerator Dry Expansion Circuit Schematic

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Refrigerator Dry Expansion Circuit Schematic

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September 6th, 2011 at 3:33 am

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Refrigerator Oil Bleed and Rectifier Schematic

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Oil bleed and rectifier for R.22 flooded evaporator

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September 6th, 2011 at 3:23 am

Posted in Refrigeration

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