Refrigerator Troubleshooting Diagram

Archive for the ‘Leak Testing’ Category

Refrigerator Service Valve

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Depending on the unit you are working on, service valves vary and will be different. Figure 26-1 shows some different service valves. Service valves are devices that allow access to the sealed refrigeration system. The most economical way this is done is by crimping. This procedure is done at the factory. A small length of copper tubing is attached to the suction side and high side of the system. When the proper amount of refrigerant charge has been placed into the system, the tubing is crimped and soldered closed. When this is completed, there isn’t a way to get back into the system. In Fig. 26-2 a crimped access is shown.

service-valve

crimping

The next type service valve is called a line-tap-valve. Figure 26-3 shows one of these. This valve is used on soft copper and doesn’t require soldering. It is installed with the use of screws. One of the disadvantages of this type of valve is its potential to leak. A small rubber “0″ ring seals the valve to the refrigerant line and is the weak link in the chain. If used on a discharge line, the valve has a limited life due to the temperature variations being applied to the rubber “0″ ring.

line-tap-valve

The most common service valve used on small equipment is the Schraeder valve. This valve is pictured in Fig. 26-4 and is very fa­miliar to all for it is used on both the low and high sides of the refrigeration system. Located in the hoses of your service manifolds are indenters. These push the core of the Schraeder valve open when the ‘/4-inch fitting is tightened onto the valve. The actual piece that holds the pressure is the valve core. The valve cores are replaceable with a valve extractor. Caution should be used when this type of valve is used on a liquid line. Liquid refrigerant has a tendency to spew when these valves are opened and closed. Burns will result if refrigerant touches your skin. If a crimped type of seal is being repaired, the Schraeder valve can be used. This valve can be acquired with a small length of copper tubing soldered to it. These access valves are soldered into place instead of crimped in the line.

schraeder-valve

The packed, angle-type valve is found in more expensive types of refrigeration equipment and air-conditioning systems. As shown in Fig. 26-5 it is entirely different from any of the previous valves mentioned. This valve has an actual valve stem that moves back and forth to open and close a valve from its seat. The valve stem passes through a gland nut on the outside of the valve. The packing within this gland nut keeps the refrigerant from leaking out of the system. A small wrench with a ratchet called a refrigeration service wrench is used to open and close this valve. On most semi-hermetic compressors this type of valve is used as the service valve and king valve on the receiver. Some versions of this valve require an Allen wrench, instead of a service wrench, for adjustment.

king-valve

This type of valve is the safest to use since you have constant control of the refrigerant.

Written by sam

October 10th, 2011 at 8:19 am

Isolation Leak Test

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For the isolation test, you will need four line access Schraeder valves with pig-tails, a drum of nitrogen, and a nitrogen regulator. One feature about the inert gas nitrogen is the fact it is not affected by temperature changes as are refrigerants. The advantage of this in testing is that the pressure placed on the system will be the same when it is checked a day or two later, regardless of what the temperature is. In Fig. 25-1 the system is divided into four segments. Each segment is sealed with an access service valve hard soldered to it.

Nitrogran is then administered to each of the four segments with the use of your service manifold and gauges. Place the exact amount of pressure required in each segment. As stated before, do not exceed the specified pressure testing amounts that the manufacturer had placed on the unit. In an R-22 system, 350 psi pressure is sufficient; for R-12 system, 250 psi pressure is sufficient. The important thing to remember about this test is that the pressure amounts should be the same in the four segments. The nitrogen should be left in the system for several days, the longer the better.

When you return to the unit, place your manifold gauges on each segment and check the pressure. The unit with the leak will natu­rally have the least pressure. This isolation test is a costly one, but it definitely confirms which section of the system has the leak. Many times, this method reveals the leak to be in the condensing unit that you checked in the beginning. This test eliminates tearing things apart for nothing. When separating the system for this test, remember you have to put it together again, so don’t destroy piping where joints will be needed to place the system back together. If the leak is found to be in one of the lines connecting the condensing unit with the evaporator unit, a new line might be run instead of trying to repair the leak in the original one. This test gives you that option by eliminating any doubt as to where the leak is.

Tests like this one will detect a leak in an evaporator coil or condensing coil. You might then remove it from the unit and seal its ends so that it may be dipped in water, just as an inner tube is tested to find a leak. A leak in a coil might be located directly under one of the fins that is attached to the tubing. Water bubbles will show exactly where the leak was. Then the fins can be cut out of the way to make the repair.

You will be dealing with copper, steel, or aluminum when making your repair. You should be familiar with the three materials. In addition to silver solder and flux, it is advisable to carry a couple of brazing rods. A can of flux or pre-fluxed rods can be used if you store them in a dry place. Many steel parts are being used in the

field such as condenser coils, receivers, accumulators, oil separators, to name a few. A rust hole or small crack can be repaired easily

with the use of a brass brazing roa. The secret in any molten metal repair is to have the surfaces of the piece to be repaired clean and dry. Many coils are being epoxy coated at the factory to extend their service life. This must be sanded from the area to be repaired very thoroughly. Aluminum solder is used extensively in the field today. It is a special solder that needs very low heat. It is expensive, yet in comparison to the cost of a evaporator coil or condensing coil, the price of the solder is cheap. The use of this solder takes practice and is difficult to teach with a written word. Practice on an old coil first. Remember, the surface must be very clean, fluxed, and low heat must be moved constantly over the repair area. The use of the oxygen-acetylene torch is a must in this industry, and you must practice to be proficient at it.

Other means of repairing aluminum have appeared on the market, some work well. A compression type of fitting is being used where a joint of steel to aluminum is made. The device works fairly well. Another type of repair is coupling two pieces of aluminum with the use of a sleeve that is sealed in the line once in position by an epoxy. This adhesive is activated by placing heat on the fitting.

isolation-leak-test

Written by sam

October 10th, 2011 at 7:52 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.

Written by sam

September 9th, 2011 at 8:02 am

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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

Written by sam

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.

Written by sam

September 6th, 2011 at 7:32 am

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Refrigerator Evaporator Unit Leak Testing

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When a thorough testing of the condensing unit doesn’t show a leak, move on to the evaporator section. Follow the same procedure as the one followed to test the condensing unit. You and the customer must be aware that leak testing of this nature is time consuming, and time is money. If the leak hasn’t been found after the condensing unit and the evaporator section have been tested, it is time to talk to the owner again. Obviously the leak is somewhere in the piping that joins the condensing section and the evaporator section. This type of repair is going to take a judgment call on your part. If the piping is mostly concealed in the floors and walls, it might be best to run new piping rather than breaking down walls and tearing up floors. It would be advisable at this point to make an isolation test.

Written by sam

December 24th, 2010 at 7:49 am

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