Capillary Tube
Just as a lawn mower motor has everything a large gas engine has but in a different form, so is a small vapor compression system similar to a large one. Large refrigerator systems use a device called an expansion valve to provide a resistance between their high and low sides. In small hermetic systems this necessary device takes the form of a small diameter pipe called the capillary tube. Internal diameters for domestic refrigerator applications range from .026 to .036 at lengths of six to twelve feet.
Purpose
To provide resistance to refrigerant flow causing a high and low pressure area within the same system. In the low pressure area ( the evaporator ) heat is absorbed, changing liquid to a vapor, and in the high pressure area ( the condenser ) heat is given off, changing the vapor back to a liquid. If no resistance were present, pressures would be the same throughout and refrigerant would circulate with no effect.
How it works
The compressor, working within the sealed system, pushes out refrigerant from one pipe and sucks from the other. First it pushes vapor into the condenser. At the end of the condenser, the capillary tube, being of small diameter, creates a resistance to flow through. As the compressor keeps pumping, the pressure rises till it levels off to a balance regulated by how much refrigerant comes in to how much is forced through the capillary. Typically, high side pressures in most systems range from 150 to 300 pounds per square inch.
On the other side of this restriction, in the evaporator, the compressor is pumping out vapor through the suction line. This causes a low pressure area ranging in most systems from zero to twenty pounds per square inch.
Locations on the cabinet
The capillary tube is attached on one end to the gas dryer, which is placed at the end of the condenser. On the other end it is attached to the evaporator inlet.
Figure 3.4 Direction of refrigerant flow through the capillary tube
How it fails
Problems are rare. However, if the system becomes contaminated with moisture due to a low side leak, acid sludge from compressor burn out, or contaminants as a result of poor repair techniques, the capillary line, due to the small diameter is the first pipe to plug up. This delicate tube can also easily rupture when subjected to mechanical damage, causing a refrigerant leak.
Please note! This discussion of a hermetic system device is included for informational purposes only. Do not attempt to repair or tamper with it in any way. To service hermetic components special equipment and knowledge is required. These types of repairs are beyond the scope of this manual. Furthermore, tampering with a hermetic system may cause the release of the ozone depleting substances that are contained in it into the atmosphere. Depending on your locality, present environmental laws now can carry strict penalties to any person who releases, or causes to be released, the common refrigerants used in domestic refrigerators.
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