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Selaed System
Chapter 1 Page 4
Capillary and Drier Filter

Under pressure from the compressor, the vapor travels through several feet of steel condensing tubing (condenser coil) before it empties into the filter drier. 

The filter drier (or just plain drier) serves two purposes. First, if filters out debris traveling with the refrigerant that could plug the capillary tube. Second, it absorbs and retains any moisture that may be mixed in with the refrigerant. As we will learn later, water is extremely harmful to any refrigeration system The outlet of the drier feeds the capillary tube. The cap tube, as it's most commonly known in the industry, is normally less than .030 inches in diameter and goes between the drier and the evaporator. 

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capillary tube.jpg

The vapor from the compressor travels through the condensing coil and drier relatively unobstructed until it reaches the cap tube. The smaller diameter tubing slows the flow of refrigerant significantly and pressure begins to build. The cap tube, therefore, meters (regulates) the flow of refrigerant into the evaporator. Because the cap tube acts as a restriction, it establishes a pressure differential between the condenser and the evaporator.

Two distinct pressure areas (dashed line) are established within the sealed system as a result of the compressor and cap tube. Low side- The compressor pulls vapor out of the evaporator, dropping Its pressure. This is the

low pressure side of the system. High Side- Because the compressor pushes vapor into the condenser and the cap tube restricts the flow of refrigerant, all of the tubing leading up to the cap tube becomes the high pressure side of the system. Pressures of a R-134a refrigerator sealed system vary greatly depending on conditions but, as a general rule, the condenser operates around the 120-130 PSIG range. The design pressure of a refrigerator evaporator is around 0 PSIG but the actual pressure is dependent on many variables but will range from about 10 inches of vacuum to 7 or 8 PSIG.  

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