Manual for Refrigeration Servicing Technicians - UNEP - Division of ...

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4 Servicing Practices Avoiding contaminants Before charging any system with refrigerant, precautions should be taken to avoid the presence of any type of contaminants in the system, so classifying contamination types in a refrigeration system is necessary to identify the proper servicing action required before charging any system with new refrigerant. First, the identification of potential contaminants is outlined: Moisture 4 Non-condensables 4 86
4 Servicing Practices Moisture Moisture causes several operating problems in RAC systems and understanding the basis of these problems is important. Basically, moisture can be classified as visible and invisible. “Visible” moisture is high concentration of water and can be seen with the eye, and is in liquid form. Occasionally, liquid water is found in systems but this is rather unusual. “Invisible” moisture is water in low concentrations and cannot be seen with the eye, since it is essentially dissolved in the refrigerant. It is important to remember that moisture can easily get into a system but it is difficult to get out. The main situations and activities that can result in moisture entering the system are: • when there is a leak in part of the system that experiences subatmospheric pressure (thus, drawing air into the system) • during servicing and repair when the system is opened and exposed to the air and evacuation is not carried out properly • when filters or lubricant are exchanged • during charging with refrigerant and transfer hoses have not been purged properly. The technician should be particularly aware of the possible introduction of moisture when carrying out these activities. There will always be some moisture within any refrigerating system, and complete elimination is almost impossible. However, at very low concentrations the moisture is unlikely to cause any significant problem. On the other hand, if the moisture is present in higher concentrations, then a series of problems can arise. The “tolerable” concentration of moisture differs between refrigerants, oil types, operating temperatures and compressor designs. Nevertheless, in almost all systems – except for ammonia systems – the maximum concentration of moisture should not exceed around 10 ppm. Above these concentrations, the moisture can have negative effects on the system, such as reactions with the oil, causing the unit to malfunction and accelerating burn-out of hermetic compressors. Recognising the presence of moisture The presence of moisture within the system can be recognised by certain observations: • The system will stop due to low suction pressure, and proceed to warm up. Since it is the formation of solid ice within the expansion device that has caused the blockage, the warming will result in the disappearance of the ice and thus the unit will work properly again. However, the process will occur again as the ice once again forms at the expansion device. • Decreasing pressure, where the suction pressure steadily decreases over several hours – even to a vacuum. Then pressure suddenly becomes normal again. This abnormal cycle will keep repeating. • If, during system shutdown, one warms the refrigerant control with a safe resistance heater (hot pad) or radiant heat bulb, the ice will melt. Should the system then begin to work properly, there is definitely moisture in the refrigerant. These symptoms are explained by the following: • The solubility of water in refrigerant reduces with temperature, so as the refrigerant passes through the expansion device, the dissolved moisture may become saturated water. 87
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Manual for Refrigeration Servicing
Page 3 and 4:
Introduction When to use the manual
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Introduction The Factors affecting
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Introduction How to assess conditio
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Introduction Characteristics of Sel
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Introduction Another form of refere
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Introduction Choose your chapter Th
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1 Environmental impact of refrigera
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1 Environmental Impact The ozone la
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1 Environmental Impact RADIATION FR
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1 Environmental Impact The ozone la
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1 Environmental Impact Effects of o
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1 Environmental Impact The greenhou
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1 Environmental Impact Timeline act
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1 Environmental Impact Alternative
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1 Environmental Impact The way forw
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2 Refrigerants 2.1. Section objecti
Page 35 and 36: 2 Refrigerants Chemical properties
Page 37 and 38: 2 Refrigerants Safety characteristi
Page 39 and 40: 2 Refrigerants Types of refrigerant
Page 41 and 42: 2 Refrigerants Those with ozone dep
Page 43 and 44: 2 Refrigerants Those with zero ozon
Page 45 and 46: 2 Refrigerants Carbon dioxide (CO2,
Page 47 and 48: 2 Refrigerants Azeotropic Blends An
Page 49 and 50: 2 Refrigerants Using Refrigerant Bl
Page 51 and 52: 2 Refrigerants Lubricants Today, al
Page 53 and 54: 2 Refrigerants Refrigerants and app
Page 55 and 56: 2 Refrigerants Properties of most c
Page 57 and 58: 3 Refrigerants Content Management M
Page 59 and 60: 3 Refrigerant Management The majori
Page 61 and 62: 3 Refrigerant Management Handling o
Page 63 and 64: 3 Refrigerant Management Recovery c
Page 65 and 66: 3 Refrigerant Management Refrigeran
Page 67 and 68: 3 Refrigerant Management Refrigeran
Page 69 and 70: 3 Refrigerant Management Open Refri
Page 71 and 72: 3 Refrigerant Management CHAPITRE 3
Page 73 and 74: 3 Refrigerant Management Recycling
Page 75 and 76: 3 Refrigerant Management equipment
Page 79 and 80: 3 Refrigerant Management PAGE 22 Ex
Page 83 and 84: 3 Refrigerant Management Further re
Page 85: Summary This section will provide t
Page 89 and 90: 4 Servicing Practices Non-condensab
Page 91 and 92: 4 Servicing Practices Evacuation A
Page 93 and 94: 4 Servicing Practices 7 - For large
Page 95 and 96: 4 Servicing Practices Pressure unit
Page 97 and 98: CHAPITRE 4 4PAGE 10 LEAK DETECTION
Page 99 and 100: 4 Servicing Practices Detection met
Page 101 and 102: 4 Servicing Practices CHAPITRE 4 PA
Page 103 and 104: 4 Servicing Practices Volumetric ch
Page 105 and 106: 4 Servicing Practices Electronic ch
Page 107 and 108: 4 Servicing Practices Why charge re
Page 109 and 110: 5 Retrofitting Content General retr
Page 111 and 112: 5 Retrofitting • Upon evaluation
Page 113 and 114: 5 Retrofitting General retrofitting
Page 115 and 116: 5 Retrofitting procedures that you
Page 117 and 118: 5 Retrofitting MVAC retrofitting pr
Page 119 and 120: 5 Retrofitting Although, in general
Page 121 and 122: 5 Retrofitting Further reading UNEP
Page 123 and 124: 6 Summary 6.1. Overview of refriger
Page 125 and 126: 6 Safe Refrigerant Handling Oxygen
Page 127 and 128: 6 Safe Refrigerant Handling The com
Page 129 and 130: 6 Safe Refrigerant Handling • Nev
Page 131 and 132: 6 Safe Refrigerant Handling Safe ha
Page 133 and 134: 6 Safe Refrigerant Handling leak de
Page 135 and 136: 6 Safe Refrigerant Handling • Lea
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6 Safe Refrigerant Handling Storage
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6 Safe Refrigerant Handling Recomme
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6 Safe Refrigerant Handling 3 - Sho
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Glossary Glossary Absolute pressure
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Glossary Fossil fuels Carbon-based
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Glossary hole in late 1985, governm
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Glossary Sealed system A refrigerat
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Acknowledgements Acknowledgements I
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Copyright Copyright © United Natio
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