ICE MACHINES Q-Model Service Manual

Refrigeration System Section 7Analyzing Why Safety Limits May Stop the IceMachineAccording to the refrigeration industry, a high percentageof compressors fail as a result of external causes. Thesecan include: flooding or starving expansion valves, dirtycondensers, water loss to the ice machine, etc. Thesafety limits protect the ice machine (primarily thecompressor) from external failures by stopping icemachine operation before major component damageoccurs.The safety limit system is similar to a high pressure cutoutcontrol. It stops the ice machine, but does not tellwhat is wrong. The service technician must analyze thesystem to determine what caused the high pressure cutout,or a particular safety limit, to stop the 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. Thismay be difficult to diagnose, as many external problemsoccur intermittently.Example: An ice machine stops intermittently on safetylimit #1 (long freeze times). The problem could be a lowambient temperature at night, a water pressure drop, thewater is turned off one night a week, etc.When a high pressure cut-out or a safety limit stops theice machine, they are doing what they are supposed todo. That is, stopping the ice machine before a majorcomponent failure occurs.Refrigeration and electrical component failures may alsotrip a safety limit. Eliminate all electrical components andexternal causes first. If it appears that the refrigerationsystem is causing the problem, use Manitowoc’sRefrigeration System Operational Analysis Table, alongwith detailed charts, checklists, and other references todetermine the cause.The following checklists are designed to assist theservice technician in analysis. However, because thereare many possible external problems, do not limit yourdiagnosis to only the items listed.7-14 Part No. 80-1100-3