Manitowoc QR0320A Service Manual page 126

Refrigeration System Section 7
Analyzing Why Safety Limits May Stop the Ice
Machine
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.
When a high pressure cut-out or a safety limit stops the
ice machine, they are doing what they are supposed to
do. That is, stopping the ice machine before a major
component failure occurs.
Refrigeration and electrical component failures may also
trip a safety limit. Eliminate all electrical components and
external causes first. If it appears that the refrigeration
system is causing the problem, use Manitowoc's
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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Part No. 80-1100-3