An evaporator coil of a single evaporator, air-cooled refrigerator is accumulating excessive frost due to a failure of the defrost mechanism. If the refrigerator features a thermostatically controlled box solenoid and a low-pressure cut-out controlled compressor, as well as a high-pressure cut-out, in terms of the compressor, what would be the most likely operating symptom?
• Effect of frost buildup on evaporator coils in an air-cooled refrigerator • How a low-pressure cut-out controls compressor operation when suction pressure drops • What happens to suction and discharge pressures when refrigerant flow through the evaporator is restricted
• As frost builds up on the evaporator, how is the airflow and heat transfer affected, and what does that do to the suction pressure at the compressor? • If the compressor is controlled by a low-pressure cut-out, what will it do when suction pressure repeatedly falls below the cut-out setting? • Which safety device (high- or low-pressure cut-out) is more likely to operate first when the evaporator is starved of heat load due to heavy frost accumulation?
• Be clear on which condition would make the low-pressure side drop versus the high-pressure side rise • Think about whether a heavily frosted coil gives the compressor too much load or effectively no load/low load • Verify which of the listed symptoms describes a compressor starting and stopping frequently due to a pressure control device.
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