Diagnosing short cycling

Welcome to the Ice-O-Matic on-line training modules.

Ice. Pure and Simple1DIAGNOSING SHORT-CYCLINGThis module will help in diagnosing possible short-cycling issues on various models of ICE Series Cubers. This module defines a short cycle as the unit entering a defrost cycle without proper ice formation on the Evaporator.

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R-1 Relay CoilRelayTimer Initiate ControlSolid State Timer DelayFirst, lets do a brief review of the sequence of operation for the 150 pound through 1000 pound production units. The Low Pressure Timer Initiate controls the untimed portion of the freeze cycle. The LPTI closes on pressure drop, energizing the Timer. The Timer will continue the freeze cycle for the length of time it is set, controlling the bridge thickness, then closes. This energizes the Relay, sending the unit into a defrost cycle.

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R-1 Relay CoilRelayTimer Initiate ControlSolid State Timer DelayShould the LPTI be set at too high of a pressure, or the Timer have insufficient time set on it, the ice formation on the Evaporator could be too thin to harvest properly. Verify the setting of the LPTI and check the accuracy of the time on the Timer. If either is inaccurate, adjust or replace the control as needed.

Ice. Pure and Simple4How to check LP Control with No Ice on the Evaporator

To check the set point of the LPTI, start by turning the unit off after a harvest. Unplug the Water Pump and set the Timer to 1 second. Now turn the selector switch to ICE. With no load on the Evaporator,the suction pressure will drop quickly. Watch your suction gauge. When the LPTI reaches its set point,it will close, energizing the Timer for only one second. The Timer will then close, starting defrost. With the opening of the Hot Gas Valve, the suction pressure will begin to rise. The lowest pressure shown on your gauge before the suction rises IS the set point of the LPTI. Verify this set point with the chart in the Technical Service Manual.

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Float ValveWater Pump ImpellerHousingWhen a unit is short cycling, it may be an indication of very poor water flow to the unit or across the Evaporator. Lack of load across the Evaporator will cause the suction pressure to dive, closing the LPTI prematurely. First, verify the water supply to the unit by pushing the float ball down. For proper water flow across the Evaporator, make sure the water level in the Trough is above the foot of the Impeller Housing during operation.

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After verifying incoming water supply at the Float, observe the water flowing from the Water Distribution Tube on the top of the Evaporator. The flow should be even and cover the entire surface of the Evaporator. If the flow is poor, check the Water Distribution Tube and Water Pump Tube for blockages and clean any found thoroughly. If none are found, the Water Pump may be the issue.Water Distribution TubeWater Pump TubeWater Inlet Float Valve

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Short cycling can also be caused by a TXV not feeding enough refrigerant to the Evaporator. Should this occur, the Evaporator will not be completely filled with refrigerant, causing poor ice formation. Generally this shows itself as ice on the bottom of the plate, but little or none at the top, with low suctionpressure and normal to elevated head pressure. A clogged or restricted Drier can also show the same symptoms. The Drier can be checked by taking the temperature of the inlet and outlet. There should be little to no difference in the temperatures.

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A system with a low charge can show the same type of ice formation as a unit with an under-feedingTXV, poor ice formation on the Evaporator. The result can be low suction and low head pressure. Inthis example, the unit is a remote system. A low charge on this type of unit will also have a hot receiver.The Mixing Valve will begin to bypass in an effort to maintain head pressure, resulting in a lack of liquid feed to the TXV, causing low suction pressure. The LPTI will close prematurely without ice formation on the Evaporator plate.

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Serpentine on back of EvaporatorShould the refrigeration coil on the back of the Evaporator, also known as the Serpentine, become separated, the result will be a hole in the ice formation on the front of the plate at the point of the separation. Should this occur, the suction pressure will dive and replacement of the Evaporator would be in order.

Ice. Pure and Simple10Diagnosing Short CyclingQuiz Ice. Pure and Simple11