A leak is a ______. Physical path or hole, usually of irregular dimensions. Name the six classes of leaks. Standing, pressure-dependent, temperature-dependent, vibration-dependent, combination-dependent, cumulative mircoleaks. Briefly describe the Standing type leak. Are leaks that can be detected while the unit is at rest or off. Briefly describe the Pressure-dependent type leak. Are leaks that can only be detected as the system pressure increases. Nitrogen is used to pressurized systems to around ____ on the low side and _____ on the high side. 150 p.s.i.g., 450 p.s.i.g. What type of gases should never be used to pressurize a system to check for leaks? Air or pure oxygen. Briefly describe the Temperature-dependent type leak. Are leaks that are associated with the heat of expansion. Briefly describe the Vibration-dependent type leak. Are leaks that only occur during the operation of the unit. Briefly describe the Combination-Dependent type leak. Are leaks that require two or more conditions in order to induce leakage. Briefly describe the Cumulative-microleaks type leak. Are leaks that are all individual leaks that are to small to detect with standard tools. What does successful leak detection depend on? The careful observation made by the testing technician. What is internally circulated with the refrigerant in a system that can aided in leak detection and why? Compressor oil. The oil will blow off with the refrigerant gas and oil marks the general area of leakage. ______ solutions are cost-effective and have been very successful in leak detection. Bubble/microfoam. As a safety precaution for leak detection: Never use _____ or ____ to raise the pressure in a refrigeration system. Pure oxygen or air. Why should you never use pure oxygen or air to raise the pressure in a refrigeration system? Pure oxygen contains about 20% oxygen. The pure oxygen and/or the oxygen in the air can combine with refrigerant oil to form an explosive mixture. What tool is not effective on HFC refrigerants and why? Halide torches, because they are used to detect chlorine, which is not present in this type of refrigerant. Describe the leak checking procedure when charging with a trace amount of refrigerant into the system. Most technicians start at 0 p.s.i.g. and introduce a refrigerant trace gas into the system until the pressure reads about 10 p.s.i.g. The pressure used to pressurize a complete system must not exceed _____. The lowest test pressure for the system. About 150 p.s.i.g. to 450 p.s.i.g. What type of tool is used with a refrigerant trace gas in the system to locate the vicinity of the leak. An electronic leak detector. What is used once the vicinity of the leak is found with the electronic leak detector, to pinpoint its exact location. Bubble/microfoam is used. What is the most basic but effective method of detecting leaks? Just listening for the rush of nitrogen and refrigerant from the connections. An EPA-certified refrigerant recovery unit must be used to remove the refrigerant for the following reasons. Up to a certain level of vacuum, which depends on the size of the system, the type of refrigerant, and whether or not it was manufactured before or after November 15, 1993. What is a good practice to perform when leak checking? Check any gauge connection ports before gauges are installed. Why should technicians not rush when trying to locate a leak? Leak detection with any device is a slow process. It takes time for the instrument to respond, so the probe must be moved slowly-about 1 in. every 2 sec is a good rate of speed. Removing air and other non-condensable gasses from a system using a vacuum pump is called ____ a system. Degassing. Removing moisture from a sealed system or product is known as _____. Dehydration. Refrigeration systems are designed to operate with only ____ and ____ circulating inside them. Refrigerant and oil. The process of removing both _______ is referred to as evacuation. Air and water vapor. Degassing + Dehydration = Evacuation. A gas that does not change into a liquid under normal operating conditions. Noncondensable gas. If a Noncondensable gas is in a system it will not condense in the condenser and move through like a liquid; instead, it will... Occupy condenser space and cause a rise in head pressure and a resulting increase in discharge temperatures and compression ratios, which produce undesirable inefficiencies. Moisture + Acid + Oil = Sludge. What will start to form after a short period of time, when moisture, heat, and refrigerant are all present in a system? Acids. Noncondensables in a system cause what types of symptoms? Head pressures and discharge temperatures to rise, oxygen from the air in a system to will react with the refrigerant oil to form organic solids. Refrigerants such as R-12, R-22 to name a few, contain either chlorine or fluorine and will hydrolyze with water, forming hydrochloric or hydrofluoric acids and more water. What happens to the system? After acids form, motor windings may deteriorate, and metal corrosion and sludge can occur. To _____ means to lower the pressure in a system below the pressure of the atmosphere. To pull a vacuum. There are _____ microns in 1 in. Hg. 25,400 To remove all of the atmosphere, which would represent a perfect vacuum, something that has never been achieved. The pressure inside the system would have to be reduced to 0 p.s.i.a. or 29.92 in. Hg vacuum. What gauge is often used to measure vacuum level. A compound gauge, it starts at 0 in. Hg vacuum and reduces to 30 in. Hg vacuum. Where should the technician attach the vacuum pump when pulling a vacuum on a refrigeration system? To the high- and the low-pressure sides of the system. The mercury column is hard to see, so another pressure measurement is called ___ is used. Micron. 1000 microns = 1 mm 1 in. = 25,400 microns Accurately measuring and proving a vacuum in the low micron range can be accomplished with an ____. Electronic instrument. When using a micron gauge how should it be positioned? The sensor should always be located in an upright position so that any oil in the system will not drain into the sensor. What is the desired vacuum range? 500 to 300 microns. When the desired vacuum is reached, what should be done next? The vacuum pump should be valved off and the reading marked. It may raise for a short period of time, about 1 min, then stabilize. What could be the case if a vacuum reading continues to rise, after valving off the vacuum pump? Either an atmospheric leak or moisture is present and is boiling to create pressure. Why should the oil in the vacuum pump must be changed regularly? For good pump performance. For best performance, why should only approved vacuum pump oil be used? Any other oil will have a boiling point that is too high and thus prevent the achievement of deep vacuums. What type of compressors are used in vacuum pumps? Rotary. The vacuum pumps that produce the lowest vacuums are ____. Two-stage rotary vacuum pumps. The usual vacuum required by manufacturers is approximately ____ microns, although some may require a vacuum as low as ____ microns. 500, 250. What happens to moisture that is in a system when a very low vacuum is pulled? It will cause it to boil to a vapor. The vapor will be removed by the vacuum pump and exhausted to the atmosphere. The deep vacuum method involves reducing the pressure in the system to about _____. 250 to 500 microns. When pressure is reduced to 250 to 500 microns and remains constant: No condensable gas or moisture is left in the system. Briefly describe the steps used for a multiple or triple evacuation. Pulled to about 1500 microns, and then bleed off a small amount of nitrogen, this is repeated about three times. The last vacuum to 250 to 500 microns and held for 10 to 15 minutes. How is a system charged while under a vacuum and why? By adding liquid refrigerant to the high side is the safest and quickest method. While a hermetic compressor is in a deep vacuum, what safety precautions should be taken? Never start it. Motor damage may occur. Before evacuation for a system with many valves and piping runs, multiple evaporators, what should be checked? To see whether the valves are open. What are system contaminants states and where are they located? Solid, liquid, or vapor and will be in the compressors oil. Because of system contaminants what is recommended for every new system field installation? A heavy-duty suction-line filter or liquid line filter dryer. Star this term You can study starred terms together What safety precautions is recommended when working with a burned-out system? Extreme caution, adequate ventilation, butyle gloves, and safety glasses for protection against acids. The oil from burnout can cause serious skin irritation and possible burns. The fumes are toxic. Why should a filter dryer be used on a recovery machine? To protect it from acids and contamination. How should the recovered refrigerant be charged back into the system? Through a filter dryer. What should be installed for system burnout cleaning procedures? Both liquid and suction lines will require a special temporary filter drier. Star this term You can study starred terms together What could get into the compressor without a good suction- and liquid-line filters or filter driers? Metal filings, shavings, dirt, flux, solder, metal chips, sand from sandpaper, bits of steel wool and wire from cleaning brushes. Please allow access to your computer’s microphone to use Voice Recording. Having trouble? Click here for help.
Posted on: Sun, 21 Sep 2014 13:27:51 +0000
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