by Ron Walker
This type of refrigeration system is usually found in where the condensing unit is located outside and the outdoor temperatures could drop below the cooler temperature. In this system there is both a solenoid and a low pressure cut-out switch. The cooling thermostat controls a solenoid connected to the liquid line inside the cooler and the low pressure cut-out switch is used to energize and de-energize the compressor. The thermostat is set to de-energize the liquid line solenoid at 35°F cooler temperature. When the solenoid is de-energized, it stops the flow of liquid to the expansion valve and the evaporator coil. The compressor will continue to run pulling the refrigerant out of evaporator coil, suction line, and part of the liquid line. All of the refrigerant is pumped into and stored in the condenser and receiver. The compressor will continue to run, pulling refrigerant out of the cooler until the suction pressure reaches the low pressure cut-out switch setting which is usually set at 2 psig. Once the cut-out pressure is reached the low pressure cut-out switch de-energizes the compressor. The evaporator fan(s) run continuously circulating cool air throughout the cooler. During the off cycle, the cooler temperature will gradually increase to the cut-in temperature of the thermostat (usually 38-39°F). When the thermostat closes it energizes the liquid line solenoid. This releases the stored refrigerant into the expansion valve, coil, and suction line. Once the suction line pressure reaches the cut-in temperature of the low pressure cut-out switch, the compressor will start and the cooling cycle will begin. As before, the condenser fan is wired in parallel with the compressor and runs whenever the compressor is energized. The system may or may not have a contactor to provide power to the compressor. The evaporator fan(s) run continuously circulating cool air through the cooler whether or not the compressor is running. Unlike a residential air conditioning system, mild frost may be present on the evaporator coil. Mild frost is not a concern as the evaporator fan(s) continue to run when the compressor is in the off cycle. Circulating 35 to 39°F air over the evaporator coil. This, above freezing, air will melt the frost on the coil during the off cycle. This is called an off-cycle defrost system with an automatic pump down cycle.
This type of refrigeration system is usually found in where the condensing unit is located outside and the outdoor temperatures could drop below the cooler temperature. In this system there is both a solenoid and a low pressure cut-out switch. The cooling thermostat controls a solenoid connected to the liquid line inside the cooler and the low pressure cut-out switch is used to energize and de-energize the compressor. The thermostat is set to de-energize the liquid line solenoid at 35°F cooler temperature. When the solenoid is de-energized, it stops the flow of liquid to the expansion valve and the evaporator coil. The compressor will continue to run pulling the refrigerant out of evaporator coil, suction line, and part of the liquid line. All of the refrigerant is pumped into and stored in the condenser and receiver. The compressor will continue to run, pulling refrigerant out of the cooler until the suction pressure reaches the low pressure cut-out switch setting which is usually set at 2 psig. Once the cut-out pressure is reached the low pressure cut-out switch de-energizes the compressor. The evaporator fan(s) run continuously circulating cool air throughout the cooler. During the off cycle, the cooler temperature will gradually increase to the cut-in temperature of the thermostat (usually 38-39°F). When the thermostat closes it energizes the liquid line solenoid. This releases the stored refrigerant into the expansion valve, coil, and suction line. Once the suction line pressure reaches the cut-in temperature of the low pressure cut-out switch, the compressor will start and the cooling cycle will begin. As before, the condenser fan is wired in parallel with the compressor and runs whenever the compressor is energized. The system may or may not have a contactor to provide power to the compressor. The evaporator fan(s) run continuously circulating cool air through the cooler whether or not the compressor is running. Unlike a residential air conditioning system, mild frost may be present on the evaporator coil. Mild frost is not a concern as the evaporator fan(s) continue to run when the compressor is in the off cycle. Circulating 35 to 39°F air over the evaporator coil. This, above freezing, air will melt the frost on the coil during the off cycle. This is called an off-cycle defrost system with an automatic pump down cycle.