Diagnosing short cycling - Ice-O

Report
Ice. Pure and Simple™
Welcome to the Ice-O-Matic® on-line training modules.
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DIAGNOSING SHORT-CYCLING
This 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
Relay
Coil
Timer Initiate
Control
Solid State Timer
Delay
First, let’s 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
Relay
Coil
Timer Initiate
Control
Solid State Timer
Delay
Should 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.
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How 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 it’s 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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Water Pump Impeller
Housing
Float Valve
When 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 ½” above the foot of the
Impeller Housing during operation.
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Water Distribution Tube
Water Pump Tube
Water Inlet Float Valve
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.
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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 suction
pressure 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-feeding
TXV, poor ice formation on the Evaporator. The result can be low suction and low head pressure. In
this 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 Evaporator
Should 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.
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Diagnosing
Short
Cycling
Quiz

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