Safety Limit Analysis - Manitowoc QuietQube SD0672C Technician's Handbook

SAFETY LIMIT ANALYSIS

According to the refrigeration industry, a high
percentage of compressors fail as a result of external
causes. These can include: flooding or starving
expansion valves, dirty condensers, water loss to the
ice machine, etc. The safety limits protect the ice
machine (primarily the compressor) from external
failures by stopping ice machine operation before
major component damage occurs.
The safety limit system is similar to a high pressure
cut-out control. It stops the ice machine, but does not
tell what is wrong. The service technician must
analyze the system to determine what caused the high
pressure cut-out, or a particular safety limit, to stop the
ice machine.
The safety limits are designed to stop the ice machine
prior to major component failures, most often a minor
problem or something external to the ice machine.
This may be difficult to diagnose, as many external
problems occur intermittently.
Example: An ice machine stops intermittently on safety
limit #1 (long freeze times). The problem could be a
low ambient temperature at night, a water pressure
drop, the water is turned off one night a week, etc.
Refrigeration and electrical component failures will
cause a safety limit trip. Eliminate all electrical
components and external causes first. If it appears
that the refrigeration system is causing the problem,
use Manitowoc's Freeze Cycle Refrigeration System
Operational Analysis Table, along with detailed charts,
checklists, and other references to determine the
cause.
The following checklists are designed to assist the
service technician in analysis. However, because
there are many possible external problems, do not
limit your diagnosis to only the items listed.
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