Compressor. The compressor is the heart of the refrigeration unit. It is a motor-operated device that circulates refrigerant much as a pump would in a sealed system. All household and many commercial refrigeration units employ hermetic compressors. (This means that the compressor with its motor are sealed in an airtight canister as opposed to belt-driven compressors.)

When energized, it creates enough pressure difference to circulate the confined refrigerant in the entire sealed system. (See fig. 1.) Through the compressor suction side, vapor refrigerant in the evaporator is drawn in and changed to hot vapor by compression. It is then forced into the condenser (through the compressor discharge tube) where it is cooled to its liquid state again before reaching the evaporator. An efficient compressor must be able to remove the refrigerant vapor at the same rate that liquid refrigerant enters the evaporator and vaporizes. The low-pressure side of the compressor is connected to a tubing having a larger diameter than that of the high-pressure side. Generally, in a regular residential unit, a good compressor should create a pressure between 15 inch of vacuum and 22 psi on the low side, and between 80 psi and 160 psi on the high side at ambient air temperature of 70°F. These pressures are checked by installing access valves (such as piercing valves) on the copper tubing on the suction and discharge lines of the compressor (see fig. 79). The installation of piercing valves mainly applies to the residential units as compressors used in most commercial systems are equipped with service valves (see figs. 32, 118, and 120). Many refrigeration problems can be diagnosed simply by checking the compressor discharge and suction pressures. The recommended high- and low-side pressures for every model of residential unit manufactured in the United States can be looked up in a reference book called Tech Master published by Master Publications.

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