Manitowoc J250 Service Manual

Also see for J-1300: Use and care manual Installation instructions

Contents

Manitowoc J250 Service Manual Manual pdf 118 page image

Section 7 Refrigeration System7-13SAFETY LIMITSGeneralIn addition to standard safety controls, such as highpressure cut-out, the control board has four built insafety limit controls which protect the ice machinefrom major component failures. New style controlboards have two safety limit controls.Safety Limit #1:If the freeze time reaches 60minutes, the control board automatically initiates aharvest cycle. If three consecutive 60-minute freezecycles occur, the ice machine stops.Safety Limit #2:If the harvest time reaches 3.5minutes, the control board automatically returns theice machine to the freeze cycle. If three consecutive3.5 minute harvest cycles occur, the ice machinestops.Safety Limit #3:if the compressor discharge linetemperature falls below 85°F/29.4C for threeconsecutive harvest cycles, the ice machine stops.Safety limit #4: If the compressor discharge linetemperature reaches 255°F/123.8°C for 15 continuosseconds during a freeze or harvest cycle the icemachine stops.Determining which safety limit stopped the icemachineWhen a safety limit condition causes the ice machineto stop, the harvest light on the control boardcontinually flashes on and off. Use the followingprocedures to determine which safety limit hasstopped the ice machine.Step 1 Move the toggle switch to off.Step 2 Move the toggle switch back to ice.Step 3 Watch the harvest light. It will flash one tofour times, corresponding to safety limits 1-4,to indicate which safety limit stopped the icemachine.After safety limit indication, the ice machine willrestart and run until a safety limit is exceededagain.Analyzing Why Safety LimitsMay Stop the Ice MachineAccording to the refrigeration industry, a highpercentage of compressors fail as a result of externalcauses. These can include: flooding or starvingexpansion valves, dirty condensers, water loss to theice machine, etc. The safety limits protect the icemachine (primarily the compressor) from externalfailures by stopping ice machine operation beforemajor component damage occurs.The safety limit system is similar to a high pressurecut-out control. It stops the ice machine, but does nottell what is wrong. The service technician mustanalyze the system to determine what caused the highpressure cut-out, or a particular safety limit, to stopthe ice machine.The safety limits are designed to stop the ice machineprior to major component failures, most often a minorproblem or something external to the ice machine.This may be difficult to diagnose, as many externalproblems occur intermittently.Example: An icemachine stops intermittently on safety limit #1 (longfreeze times). The problem could be a low ambienttemperature at night, a water pressure drop, the wateris turned off one night a week, etc.When a high pressure cut-out or a safety limit stopsthe ice machine, they are doing what they aresupposed to do. That is, stopping the ice machinebefore a major component failure occurs.Refrigeration and electrical component failures mayalso trip a safety limit. Eliminate all electricalcomponents and external causes first. If it appearsthat the refrigeration system is causing the problem,use Manitowoc’s Refrigeration System OperationalAnalysis Table, along with detailed charts, checklists,and other references to determine the cause.The following checklists are designed to assist theservice technician in analysis. However, becausethere are many possible external problems, do notlimit your diagnosis to only the items listed.