Service manual

Refrigeration System Section 7
7-14
Part No. 80-1100-3
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.